I want you to be my neet pg mentor i want under 5000 rank in it guide me and prepare high yield revision notes for 19subjects start with microbiology use buzzwords fact based investigations of choice characteristic findings and include everything also give pyq and high yield

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NEET PG 2025 microbiology high yield topics PYQ important

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🧫 NEET PG MICROBIOLOGY - HIGH YIELD REVISION NOTES

Target: Under 5000 Rank | Your NEET PG Mentor Guide

HOW TO USE THESE NOTES

Buzzwords are in bold - these trigger answers in MCQs
★★★ = Must-know (appears every year)
★★ = Frequently asked
★ = Occasional
PYQ tags indicate previously asked question type

SECTION 1: BACTERIOLOGY

🟡 GRAM-POSITIVE COCCI

STAPHYLOCOCCUS AUREUS ★★★

Buzzwords: Coagulase +, Catalase +, Protein A, MRSA, Mannitol salt agar, Golden yellow pigment

Feature	Detail
Gram stain	Gram +ve cocci in clusters (grape-like)
Media	Mannitol salt agar (selective), Blood agar (beta-hemolysis)
Key enzyme	Coagulase (distinguishes from CoNS)
Protein A	Binds Fc of IgG → inhibits opsonization
Pigment	Golden yellow (aureus = gold)
Catalase	Positive (differentiates from Streptococcus)

Toxins (HIGH YIELD TABLE):

Toxin	Disease	Mechanism
Exfoliative toxin (ETA, ETB)	SSSS (Scalded Skin Syndrome)	Serine protease → cleaves desmoglein-1 (epidermis splits)
TSST-1 (Toxic Shock Syndrome Toxin)	TSS	Superantigen → massive cytokine release
Enterotoxin (A-E, SE)	Food poisoning (rapid onset 2-6 hrs)	Preformed toxin, heat stable, superantigen
Panton-Valentine Leukocidin (PVL)	CA-MRSA, necrotizing pneumonia, furunculosis	Pore-forming toxin → leukocyte lysis
Alpha toxin	Membrane pore formation, dermonecrosis	—

Diseases:

SSSS → Nikolsky sign +ve, infants, cleavage in stratum granulosum (NOT subepidermal like TEN)
Food poisoning → fastest onset (2-6 hrs), nausea/vomiting without fever, heat-stable toxin (cooking doesn't destroy)
Endocarditis → IV drug users → tricuspid valve (right-sided), prosthetic valve infections
Osteomyelitis → MCC in children, hematogenous spread, metaphysis of long bones
Nasal carrier: anterior nares

Treatment:

Community MRSA: TMP-SMX, doxycycline, clindamycin, linezolid
Hospital MRSA: Vancomycin (IV, DOC), alternatives: daptomycin, linezolid, tigecycline
MSSA: Nafcillin/oxacillin (beta-lactamase resistant penicillins)
Vancomycin resistance mediated by: VanA gene (acquired from Enterococcus)

PYQ-type: "A neonate develops bullous lesions with Nikolsky sign. Organism?" → S. aureus (exfoliative toxin, SSSS) "Food poisoning 2 hrs after party meal, no fever?" → S. aureus preformed enterotoxin

STREPTOCOCCUS PYOGENES (Group A Strep) ★★★

Buzzwords: Beta-hemolysis, Bacitracin sensitive, ASO titer, M protein, PANDAS

Feature	Detail
Group	Lancefield Group A
Hemolysis	Beta-hemolysis
Sensitivity	Bacitracin sensitive (PYD test +ve)
Key virulence	M protein (antiphagocytic, main virulence factor)
Toxin	Streptolysin O (ASO titer) → cardiotoxic; Streptolysin S (oxygen-stable)

Diseases:

Pharyngitis → MCC bacterial pharyngitis
Impetigo → Most common skin infection in children (GAS or S. aureus)
Scarlet fever → Erythrogenic toxin (pyrogenic exotoxin A/B/C); strawberry tongue, sandpaper rash, Pastia's lines in skin folds
Rheumatic Fever → Post-strep, Jones criteria, ASO titer elevated; Aschoff bodies (pathognomonic)
PSGN → Post-strep GN, low complement (C3), nephritic syndrome, anti-DNase B
Necrotizing fasciitis → Type II (GAS alone)
PANDAS: Pediatric Autoimmune Neuropsychiatric Disorders

Key distinguishing tests:

Bacitracin sensitive = Group A (pyogenes)
Bacitracin resistant = Group B (agalactiae)
Optochin sensitive = S. pneumoniae
Bile solubility +ve = S. pneumoniae

PYQ-type: "Pastia lines, strawberry tongue after sore throat?" → Scarlet fever, S. pyogenes "Jones criteria + ASO titer elevated?" → Rheumatic Fever

STREPTOCOCCUS PNEUMONIAE ★★★

Buzzwords: Optochin sensitive, Bile soluble, Quellung reaction, Rusty sputum, Diplococci, Quelling

Feature	Detail
Morphology	Lancet-shaped diplococci (gram +ve)
Capsule	Polysaccharide (main virulence factor, antiphagocytic)
Test	Optochin sensitive, Bile soluble
Special test	Quellung reaction (capsular swelling with specific antibody)

Diseases:

Lobar pneumonia → rusty/prune juice sputum, MCC in adults
Meningitis → MCC in adults, elderly; Indian ink stain NOT done here (that's for Cryptococcus)
Otitis media → MCC
Sinusitis → MCC
Septicemia → especially in asplenic patients (OPSI - Overwhelming Post-Splenectomy Infection)

Vaccine: PCV13 (conjugate, T-cell dependent) / PPSV23 (polysaccharide, T-cell independent) Resistance: PBP2x mutation → penicillin resistance Treatment: Penicillin (sensitive strains); Ceftriaxone + Vancomycin for meningitis

PYQ-type: "Most common cause of lobar pneumonia?" → S. pneumoniae "Asplenic patient with sepsis?" → S. pneumoniae (encapsulated bacteria)

STREPTOCOCCUS AGALACTIAE (Group B) ★★

Buzzwords: CAMP test, Neonatal meningitis, Neonatal sepsis, Group B

Neonatal sepsis + meningitis (MCC in neonates along with E. coli)
CAMP test +ve (arrowhead hemolysis with S. aureus)
Bacitracin resistant
Screening: vaginal swab at 35-37 weeks pregnancy
Treatment: Ampicillin (intrapartum prophylaxis)

ENTEROCOCCUS ★★

Buzzwords: PYP test, NaCl tolerance, UTI hospital, VRE

Grows in 6.5% NaCl and bile (PYP test +ve)
MCC of hospital-acquired UTI (with E. coli as community)
VRE (Vancomycin-Resistant Enterococcus) → VanA gene → transferred vancomycin resistance to MRSA
Treatment of VRE: Linezolid, daptomycin, tigecycline

🔵 GRAM-NEGATIVE COCCI

NEISSERIA MENINGITIDIS ★★★

Buzzwords: Waterhouse-Friderichsen, Meningococcemia, petechiae, chocolate agar, oxidase +ve

Feature	Detail
Media	Chocolate agar, Thayer-Martin medium
Oxidase	Positive
Capsule	Polysaccharide (serogroups A, B, C, W, Y, X)
Carrier site	Nasopharynx
Fermentation	Ferments glucose AND maltose (key: maltose differentiates from N. gonorrhoeae)

Diseases:

Meningitis → MCC in young adults (college students); serogroup B (most common in developed countries), A (sub-Saharan Africa)
Meningococcemia → petechial/purpuric rash, DIC, shock
Waterhouse-Friderichsen syndrome → bilateral adrenal hemorrhage, fulminant septicemia
Complement deficiency (C5-C9) → recurrent Neisseria infections

PYQ-type: "College student with neck stiffness, petechial rash, bilateral adrenal hemorrhage?" → N. meningitidis, Waterhouse-Friderichsen

NEISSERIA GONORRHOEAE ★★★

Buzzwords: STI, oxidase +ve, chocolate agar, intracellular diplococci, Thayer-Martin, PID

Feature	Detail
Key	No polysaccharide capsule (no herd immunity from vaccine until recently)
Pili	Main virulence factor
Fermentation	Glucose only (NOT maltose - key differentiator from N. meningitidis)
Media	Thayer-Martin (modified chocolate agar + vancomycin, colistin, nystatin)

Diseases:

Urethritis → gram -ve intracellular diplococci in PMNs
PID → salpingitis, Fitz-Hugh-Curtis syndrome (perihepatitis, violin-string adhesions)
Ophthalmia neonatorum → MCC bacterial conjunctivitis in newborns (within 24-48 hrs)
Septic arthritis → MCC in sexually active young adults (disseminated gonococcal infection)
Arthritis-dermatitis syndrome → migratory polyarthritis, tenosynovitis, vesiculopustular skin lesions

Treatment:

Uncomplicated: Ceftriaxone 500 mg IM single dose (+ Doxycycline if chlamydia not excluded)
Ophthalmia neonatorum prophylaxis: Erythromycin eye ointment (or silver nitrate historically - Credé's method)

PYQ-type: "STI patient with intracellular gram-negative diplococci in PMNs?" → N. gonorrhoeae "Newborn conjunctivitis day 1-4?" → Gonorrhea (chemical - silver nitrate, day 5+ Chlamydia)

🟢 GRAM-POSITIVE RODS

CLOSTRIDIUM TETANI ★★★

Buzzwords: Drumstick/tennis racquet spore, Tetanospasmin, GABA block, Trismus, Lockjaw

Feature	Detail
Morphology	Drumstick/tennis racquet spore (terminal spore)
Toxin	Tetanospasmin (tetanus toxin) = TeNT
Mechanism	Blocks GABA and glycine release at Renshaw cells → spastic paralysis
Retrograde transport	Toxin travels via peripheral nerves to CNS

Diseases:

Generalized tetanus → Trismus (lockjaw), risus sardonicus, opisthotonus, spasms
Neonatal tetanus → contaminated umbilical cord stump
Local tetanus → confined to area of wound
Cephalic tetanus → CN involvement, trismus + facial palsy

Characteristic: C. tetani does NOT invade tissue - produces toxin locally Treatment: Wound debridement + TIG (Tetanus Immunoglobulin) + Metronidazole + Diazepam (muscle relaxant) + Active immunization

PYQ-type: "Spastic paralysis after wound, blocks GABA, drumstick spore?" → C. tetani

CLOSTRIDIUM BOTULINUM ★★★

Buzzwords: Botulin, Flaccid paralysis, Honey infant, ACh block, Presynaptic

Feature	Detail
Toxin	Botulinum toxin (most potent known toxin)
Mechanism	Blocks ACh release at NMJ (presynaptic) → flaccid paralysis
Types	A, B, E, F cause human disease; Type A most common food-borne
Route	Cleaves SNARE proteins (SNAP-25, VAMP, syntaxin)

Forms:

Food-borne → home-canned foods, preserved meats
Infant botulism → honey ingestion (<1 yr), floppy baby, constipation, MCC of sudden unexpected death in infancy (SUDI) (honey)
Wound botulism → IV drug users, black tar heroin
Iatrogenic → cosmetic (Botox, Type A)

Triad: Descending flaccid paralysis + no fever + intact sensorium Diagnosis: Mouse bioassay (gold standard) - serum, stool Treatment: Antitoxin (trivalent ABE) + supportive; Infant botulism: Human BIG (Baby BIG) = Botulism Immune Globulin

PYQ-type: "Infant with flaccid paralysis after honey exposure, constipation, descending?" → Infant botulism "Blocks ACh presynaptically vs tetanus (blocks GABA)?" → Classic PYQ comparison

CLOSTRIDIUM PERFRINGENS ★★★

Buzzwords: Alpha toxin (lecithinase), Gas gangrene, Double zone hemolysis, Nagler test

Feature	Detail
Type	Type A → gas gangrene, food poisoning
Key toxin	Alpha toxin = Lecithinase (phospholipase C) → main virulence
Test	Nagler test (alpha toxin on egg yolk agar → opacity inhibited by antitoxin)
Hemolysis	Double zone of hemolysis on blood agar
Spore	Subterminal spore

Diseases:

Gas gangrene (Clostridial myonecrosis) → crepitant wound, gas in tissues (X-ray), rapid progression
Food poisoning → Type A, enterotoxin, 8-24 hrs onset, watery diarrhea, no vomiting (unlike S. aureus)
Necrotizing enterocolitis (Type C, beta toxin)

PYQ-type: "Lecithinase, double zone, gas in wound?" → C. perfringens

CLOSTRIDIUM DIFFICILE ★★★

Buzzwords: Pseudomembranous colitis, Antibiotic-associated diarrhea, Toxin A+B, Rifaximin, Vancomycin oral

Feature	Detail
Toxin A	Enterotoxin (diarrhea, fluid secretion)
Toxin B	Cytotoxin (cell death, more potent, gold standard detection)
Binary toxin	CDT toxin in hypervirulent NAP1/B1/027 strain
Trigger	Clindamycin (historically), also fluoroquinolones, cephalosporins, ampicillin

Diagnosis:

GDH antigen (screening) + Toxin A/B EIA (confirmation)
Cell cytotoxicity assay (gold standard for toxin B)
Stool culture (slow, not routine)
Colonoscopy: Yellowish pseudomembranes

Treatment:

Mild-moderate: Oral Vancomycin or Fidaxomicin (DOC, least recurrence)
Severe: Vancomycin PO + Metronidazole IV
Fecal Microbiota Transplant (FMT) → recurrent CDI (highly effective)
Bezlotoxumab (anti-Toxin B monoclonal antibody) → prevention of recurrence

PYQ-type: "Diarrhea after clindamycin therapy, pseudomembranes on colonoscopy?" → C. difficile PMC

BACILLUS ANTHRACIS ★★★

Buzzwords: Bamboo stick/Medusa head colony, Bioterrorism, Anthrax, Antiphagocytic capsule (D-glutamate)

Feature	Detail
Capsule	Poly-D-glutamic acid (unusual - only bacterium with amino acid capsule)
Toxin	EF (Edema Factor) + PA (Protective Antigen) = Edema toxin; LF (Lethal Factor) + PA = Lethal toxin
Colony	Bamboo stick / Medusa head (non-hemolytic, non-motile)
Spore	Central spore

Forms:

Cutaneous anthrax (most common 95%) → malignant pustule → black eschar (painless)
Inhalational/Woolsorter's disease → widened mediastinum on CXR (mediastinal hemorrhagic lymphadenitis)
GI anthrax → contaminated meat
Anthrax meningitis → hemorrhagic meningitis

Treatment: Ciprofloxacin or Doxycycline; Post-exposure prophylaxis same Vaccine: AVA (Anthrax Vaccine Adsorbed), protective antigen-based

PYQ-type: "Painless black eschar after animal hide exposure?" → Cutaneous anthrax "Widened mediastinum + bioterrorism?" → Inhalation anthrax

CORYNEBACTERIUM DIPHTHERIAE ★★★

Buzzwords: Diphtheria toxin, ADP-ribosylation, EF-2, Metachromatic granules, Bull-neck, Pseudomembrane

Feature	Detail
Morphology	Chinese letter / V/L shaped arrangement, metachromatic granules (Babes-Ernst bodies)
Stain	Albert's stain (granules appear green/blue-black), Neisser's stain
Media	Loeffler's serum slope (growth in 6-8 hrs) + Tellurite agar (black colonies)
Toxin mechanism	ADP-ribosylation of EF-2 (elongation factor 2) → inhibits protein synthesis
Toxin gene	Beta-prophage (tox gene) → lysogenic conversion

Diseases:

Pharyngeal diphtheria → gray/white pseudomembrane (bleeds on removal), bull-neck (cervical lymphadenopathy + edema), stridor
Myocarditis → most common cause of death (cardiac complications)
Neuropathy → demyelinating; palatal palsy (earliest), accommodation palsy (ciliary muscle), late peripheral neuropathy
Cutaneous diphtheria → C. ulcerans (zoonotic, same toxin)

Schick test: Tests immunity (not diagnosis) - historical Treatment: Diphtheria Antitoxin (DAT) (most important, given urgently) + Erythromycin or Penicillin

PYQ-type: "ADP ribosylation of EF-2, grey membrane, bull neck?" → C. diphtheriae "Toxin of diphtheria encoded by?" → Beta-bacteriophage (lysogenic conversion)

LISTERIA MONOCYTOGENES ★★★

Buzzwords: Cold enrichment, Tumbling motility, Unpasteurized cheese, Neonatal meningitis, Actin rockets

Feature	Detail
Motility	Tumbling motility at 25°C; Actin rocket motility intracellularly
Growth	Cold enrichment (grows at 4°C - refrigerator!)
Hemolysis	Beta-hemolysis on blood agar
CAMP test	Positive (synergistic hemolysis with S. aureus, opposite quadrant to Group B Strep)

At risk populations:

Neonates (MCC of neonatal meningitis with Group B Strep, also E. coli)
Pregnant women → granulomatosis infantiseptica (stillbirth, granulomas)
Elderly, immunocompromised
Foodborne: unpasteurized dairy, deli meats, coleslaw

Treatment: Ampicillin (DOC); Note: naturally resistant to cephalosporins

PYQ-type: "Neonatal meningitis + cold enrichment + tumbling motility?" → Listeria monocytogenes

🔴 GRAM-NEGATIVE RODS (ENTEROBACTERIACEAE)

ESCHERICHIA COLI ★★★

Buzzwords: UTI MCC, Traveler's diarrhea, ETEC, EHEC O157:H7, HUS, Lac+, MacConkey

Pathotype	Disease	Key Feature
ETEC	Traveler's diarrhea	ST (heat-stable, cGMP) + LT (heat-labile, cAMP, like cholera)
EPEC	Infant diarrhea	Attaching-effacing lesions, no toxin, no invasion
EHEC (O157:H7)	HUS (Hemolytic Uremic Syndrome)	Shiga-like toxin, bloody diarrhea, NO antibiotics
EIEC	Dysentery-like	Invades colon (like Shigella)
EAEC	Persistent diarrhea	Biofilm, "stacked brick" pattern

UTI: MCC of community-acquired UTI Neonatal meningitis: K1 capsular antigen (cross-reacts with group B meningococcus) MacConkey agar: Pink colonies (lac+)

HUS triad: Microangiopathic hemolytic anemia + Thrombocytopenia + Acute renal failure Avoid antibiotics in EHEC (SLT release increases → worse HUS)

PYQ-type: "Bloody diarrhea + renal failure in child after undercooked beef?" → EHEC O157:H7, HUS "Traveler's diarrhea, rice water-like, cAMP mechanism?" → ETEC

SALMONELLA ★★★

Buzzwords: Typhoid, Rose spots, Widal test, H2S +ve, Non-lac, Intracellular, Bone marrow culture

Species	Disease
S. typhi	Typhoid fever
S. paratyphi A,B,C	Paratyphoid
S. typhimurium/enteritidis	Gastroenteritis (non-typhoidal)

Typhoid fever:

1st week: Bacteremia → blood culture (most sensitive in 1st week)
2nd week: Widal test positive (O and H antibodies), Rose spots (faint pink macules, anterior abdomen), constipation (then diarrhea)
3rd week: Complications: intestinal perforation + hemorrhage (Peyer's patches)
4th week: Resolution or relapse

Widal test: O antibodies (somatic) + H antibodies (flagellar); >1:160 significant (not diagnostic alone) Best culture: Bone marrow culture (most sensitive throughout disease; 80-90%) Carrier: Gallbladder (bile = carrier site); treated with ciprofloxacin

Treatment: Ceftriaxone (DOC parenteral), Azithromycin (outpatient/oral), ciprofloxacin (resistance common) Vaccine: Ty21a (live oral), Vi capsular polysaccharide (inject), Vi-TT conjugate (Typbar-TCV) - latest, preferred in children

PYQ-type: "Relative bradycardia, rose spots, step-ladder fever?" → Typhoid "Best culture in 1st week of typhoid?" → Blood culture "Best culture overall in typhoid?" → Bone marrow

SHIGELLA ★★★

Buzzwords: Dysentery, No H2S, No motility, No lactose, Shiga toxin, Smallest ID, Low inoculum

Feature	Detail
Motility	Non-motile
H2S	Negative (key difference from Salmonella)
Inoculum	Lowest infectious dose (~10-100 organisms)
Toxin	Shiga toxin (S. dysenteriae type 1) = same as SLT of EHEC
Spread	Feco-oral, person-to-person

Species (4 serogroups):

S. dysenteriae (Group A) - most severe, Shiga toxin
S. flexneri (Group B) - MCC in India/developing countries
S. boydii (Group C)
S. sonnei (Group D) - MCC in developed countries, mildest

Disease: Bacillary dysentery → crampy pain, tenesmus, blood + mucus in stool, fever Complications: HUS (Shiga toxin), Reiter's syndrome, toxic megacolon

Treatment: Azithromycin (DOC in children), ciprofloxacin (adults); important - DO treat (unlike EHEC)

PYQ-type: "Smallest infectious dose, bloody diarrhea, non-motile gram-negative rod?" → Shigella

VIBRIO CHOLERAE ★★★

Buzzwords: Rice water stool, El Tor, O1/O139, CTX phage, cAMP, TCBS, Comma-shaped

Feature	Detail
Morphology	Comma-shaped (vibrio), darting motility
Media	TCBS (Thiosulfate Citrate Bile Salt Sucrose agar) → yellow colonies (V. cholerae, sucrose +ve)
Toxin mechanism	CT (cholera toxin) → ADP ribosylates Gsα → ↑cAMP → ↑Cl- secretion
Toxin gene	CTXφ (filamentous bacteriophage) → lysogenic conversion
Virulence cluster	VPI-1 (Vibrio Pathogenicity Island) → TCP pilus
Serogroup	O1 (El Tor biotype - current pandemic) + O139 (Bengal)

Disease:

Profuse watery "rice water" diarrhea (no blood, no pus = secretory diarrhea)
Severe dehydration → "washerwoman's hands," "sunken eyes"
No invasion, no inflammation

El Tor vs Classical: El Tor (milder, carrier state more common, current 7th pandemic) O139: First non-O1 to cause epidemic cholera, no cross-immunity with O1

Treatment: Oral Rehydration Therapy (ORT) = cornerstone; Antibiotics: Doxycycline (single dose, adults), tetracycline; reduces duration

PYQ-type: "Rice water stools, ADP ribosylates Gsα, cAMP increase?" → V. cholerae "Yellow colonies on TCBS, O1 El Tor?" → V. cholerae

HELICOBACTER PYLORI ★★★

Buzzwords: Urease +ve (most), CLO test, Bismuth, Triple therapy, PUD, MALT lymphoma, Gastric cancer

Feature	Detail
Morphology	Spiral-shaped (helical), gram-negative
Urease	Strongly urease +ve (most clinically relevant feature)
Media	Skirrow's medium (selective), microaerophilic conditions
Tests	CLO test (rapid urease test on biopsy), UBT (Urea Breath Test) (non-invasive, best for follow-up), Stool antigen (non-invasive), Serology

Associations:

Peptic ulcer disease (90% duodenal, 70% gastric)
MALT lymphoma (H. pylori eradication can cure early MALT lymphoma!)
Gastric adenocarcinoma (WHO Group 1 carcinogen)
Non-ulcer dyspepsia

Treatment (Triple therapy): PPI + Clarithromycin + Amoxicillin x 14 days Quadruple therapy: PPI + Bismuth + Metronidazole + Tetracycline (resistance)

PYQ-type: "MALT lymphoma cured by antibiotics?" → H. pylori eradication "Non-invasive test of choice to confirm eradication?" → Urea Breath Test (UBT)

🟤 MYCOBACTERIA

MYCOBACTERIUM TUBERCULOSIS ★★★

Buzzwords: AFB, Ziehl-Neelsen, Lowenstein-Jensen, Ghon focus, Caseous necrosis, Cord factor, PPD/Mantoux

Feature	Detail
Stain	Ziehl-Neelsen → red bacilli on blue background (acid-fast = retain carbol fuchsin)
Fluorescent	Auramine-rhodamine (more sensitive screening)
Media	Lowenstein-Jensen (LJ) medium → buff/cream colonies, 6-8 weeks
BACTEC	Liquid culture (faster, 9-14 days)
Cell wall	Mycolic acids (high lipid content → acid-fastness, slow growth, resistance)

Key virulence factors:

Cord factor (trehalose 6,6-dimycolate) → serpentine cording in vitro, inhibits phagosome-lysosome fusion
Sulfatides → inhibit phagolysosome fusion
LAM (Lipoarabinomannan) → inhibits macrophage activation

Pathogenesis:

Ghon focus = primary focus in lung (lower lobe of upper / upper lobe of lower)
Ghon complex = Ghon focus + regional lymph nodes
Simon focus = hematogenous seeding of apex (later reactivation site)
Ranke complex = calcified Ghon complex + lymph nodes

Tuberculin test (Mantoux/PPD):

0.1 mL 5TU PPD intradermally
Read at 48-72 hours
≥10 mm = positive (general); ≥5 mm in HIV/immunocompromised/close contact; ≥15 mm in low-risk individuals
False positive: BCG, NTM (non-tuberculous mycobacteria)
False negative: Miliary TB, severe malnutrition, HIV, sarcoidosis, measles

IGRA (Interferon Gamma Release Assay): QuantiFERON-TB Gold; Not affected by BCG; Preferred in BCG-vaccinated

Treatment (standard):

2HRZE + 4HR (2 months Isoniazid + Rifampicin + Pyrazinamide + Ethambutol, then 4 months HR)
INH + Rifampicin = most bactericidal combination (sterilizing activity)
Pyrazinamide = sterilizing activity (kills semi-dormant bacilli)
Ethambutol = prevents resistance (visual side effect → optic neuritis)

Side effects (HIGH YIELD):

Drug	Key Side Effect
Isoniazid (INH)	Peripheral neuropathy (B6 deficiency) → give pyridoxine; hepatotoxicity; drug-induced lupus
Rifampicin	Orange discoloration of body fluids; Hepatotoxicity; potent CYP450 inducer → OCP failure
Pyrazinamide	Hyperuricemia (gout); hepatotoxicity
Ethambutol	Retrobulbar optic neuritis → color vision (red-green) loss, visual acuity loss
Streptomycin	Ototoxicity (vestibular > cochlear), nephrotoxicity

PYQ-type: "TB drug causing peripheral neuropathy?" → INH (pyridoxine deficiency) "Drug causing red-green color blindness?" → Ethambutol "Drug contraindicated in pregnancy?" → Streptomycin (ototoxic to fetus) "Rifampicin + OCP?" → Decreased OCP efficacy (CYP inducer)

MYCOBACTERIUM LEPRAE ★★★

Buzzwords: Cannot culture, Armadillo, Globi, Fite-Faraco, Leonine facies, Lucio phenomenon

Feature	Detail
Culture	Cannot be cultured in vitro (grows in mouse footpad, armadillo)
Stain	Fite-Faraco stain (modified ZN)
Appearance	Globi (bundles of bacilli in macrophages = lepra cells/Virchow cells)
Temperature	Grows best at 27-30°C (cool extremities)

Types:

Type	Immunity	Bacilli	Lepromin	Features
Tuberculoid (TT)	High CMI	Few (paucibacillary)	+ve	Hypopigmented anesthetic patches, nerve thickening
Lepromatous (LL)	Low CMI	Many (multibacillary)	-ve	Leonine facies, madarosis, orchitis, Virchow cells, glove-stocking anesthesia
Borderline (BL/BT/BB)	Variable	Variable	Variable	Unstable, reactions common

Lepromin test (Mitsuda test): Tests cellular immunity (NOT diagnosis)

Fernandez reaction (48 hrs) = type IV hypersensitivity
Mitsuda reaction (28 days) = granuloma formation

Complications:

Type 1 reaction (Reversal) → Borderline forms, sudden upgrading
Type 2 reaction (ENL - Erythema Nodosum Leprosum) → Lepromatous, immune complex (type III), treat with Thalidomide
Lucio phenomenon → severe necrotizing vasculitis in Lucio leprosy (diffuse LL)

Treatment (MDT - Multi Drug Therapy):

PB (Paucibacillary): Dapsone + Rifampicin x 6 months
MB (Multibacillary): Dapsone + Rifampicin + Clofazimine x 12 months

PYQ-type: "Lepromin +ve, paucibacillary, anesthetic patch?" → Tuberculoid leprosy "ENL reaction in leprosy treated by?" → Thalidomide

🟠 OTHER IMPORTANT BACTERIA

HAEMOPHILUS INFLUENZAE ★★★

Buzzwords: Chocolate agar, X+V factor, Satellite phenomenon, Polysaccharide capsule type b, Epiglottitis

Feature	Detail
Growth factors	X factor (hemin) + V factor (NAD) - both required for H. influenzae
Media	Chocolate agar (releases X+V factors); Levinthal's agar (for capsule typing)
Satellite phenomenon	Grows around S. aureus streak on blood agar (S. aureus provides V factor)

Diseases:

Epiglottitis → type b strain; "cherry red epiglottis," thumbprint sign on lateral neck X-ray, high fever, drooling, stridor; DO NOT examine throat (can cause complete obstruction)
Meningitis → was MCC in children <5 yrs (now rare post-Hib vaccine)
Otitis media, sinusitis → non-typeable strains (MCC overall in adults)
Cellulitis → "brawny" blue-red cellulitis on face/head in young children

Vaccine: Hib vaccine (conjugate polysaccharide, T-cell dependent) → dramatically reduced type b disease

PYQ-type: "Thumbprint sign on lateral neck X-ray, child with drooling?" → Epiglottitis, H. influenzae type b

BORDETELLA PERTUSSIS ★★★

Buzzwords: Whooping cough, 100-day cough, Bordet-Gengou agar, Filamentous hemagglutinin, Lymphocytosis

Feature	Detail
Media	Bordet-Gengou agar (potato blood glycerol agar) → mercury droplet / bisected pearl colonies
Key toxin	Pertussis toxin (PT) → ADP-ribosylates Gi (inhibitory G-protein) → ↑cAMP
Other toxins	Filamentous hemagglutinin (FHA) (main adhesin), Tracheal cytotoxin, Adenylate cyclase toxin

Disease stages:

Catarrhal stage (1-2 weeks) → like common cold, most infectious
Paroxysmal stage (2-6 weeks) → inspiratory whoop, posttussive vomiting, lymphocytosis (absolute)
Convalescent → gradual recovery

Complications: Pneumonia (MCC death), encephalopathy, subconjunctival hemorrhage, inguinal hernia Treatment: Azithromycin (DOC); macrolides erythromycin (contraindicated in infants <1 month → pyloric stenosis)

PYQ-type: "Absolute lymphocytosis + paroxysmal cough + whoop?" → Pertussis "Mercury droplet colony morphology?" → Bordetella pertussis

PSEUDOMONAS AERUGINOSA ★★★

Buzzwords: Grape-like odor, Blue-green pigment, Burn patients, CF, Hot tub folliculitis, Meropenem

Feature	Detail
Pigments	Pyocyanin (blue-green), Pyoverdin/fluorescein (yellow-green, fluorescent)
Odor	Grape-like / fruity (2-aminoacetophenone)
Media	MacConkey (non-lac fermenter, colorless colonies)
Resistance	Intrinsic resistance to many antibiotics; biofilm formation

Diseases:

Burns → most dangerous nosocomial pathogen in burns
Cystic fibrosis → mucoid strains (alginate overproduction), chronic colonization
Nosocomial pneumonia (VAP - ventilator-associated)
Otitis externa ("Swimmer's ear"), Malignant otitis externa (diabetics, elderly)
Hot tub folliculitis (serotype O:11)
Ecthyma gangrenosum → black necrotic skin lesion in immunocompromised (bacteremia)

Treatment: Anti-pseudomonal beta-lactam (piperacillin-tazobactam, ceftazidime, cefepime, meropenem) + Aminoglycoside or fluoroquinolone (ciprofloxacin)

PYQ-type: "Blue-green pus in burn wound, grape-like odor?" → Pseudomonas aeruginosa "Ecthyma gangrenosum in neutropenic patient?" → P. aeruginosa bacteremia

SECTION 2: VIROLOGY

HIV ★★★

Buzzwords: CD4, CXCR4/CCR5, Reverse transcriptase, p24, ELISA+Western blot, Window period, ART

Feature	Detail
Family	Retroviridae (lentivirus)
Genome	ssRNA (+sense), diploid (2 copies)
Envelope	gp120 (attachment to CD4), gp41 (fusion)
Key enzyme	Reverse transcriptase (RNA→DNA), Integrase, Protease
Co-receptors	CXCR4 (T-tropic, X4 strains) + CCR5 (M-tropic, R5 strains); CCR5 Δ32 mutation → resistance to HIV

Window period: 3-12 weeks (ELISA becomes positive) 4th generation ELISA: Detects both p24 antigen + antibody → reduces window period

HIV staging (CD4 count):

>500/mm³ → asymptomatic
200-500 → early symptoms, constitutional
<200 → AIDS-defining (PCP, MAI, CMV, Cryptococcus, Toxoplasma)
<50 → CMV retinitis, MAC disseminated

AIDS-defining illnesses (IMPORTANT):

PCP (Pneumocystis jirovecii) → CD4 <200, GGO on HRCT, LDH elevated, BAL diagnosis, TMP-SMX treatment
CMV retinitis → CD4 <50, "pizza pie" / "cheese and ketchup" retina, Ganciclovir
Toxoplasma encephalitis → CD4 <100, ring-enhancing lesions, Pyrimethamine + Sulfadiazine
Cryptococcal meningitis → CD4 <100, India ink +ve, latex agglutination (capsular antigen = most sensitive), Amphotericin B + Flucytosine
MAC (Mycobacterium avium complex) → CD4 <50, disseminated, Azithromycin (prophylaxis), Clarithromycin + Ethambutol + Rifabutin (treatment)

ART drugs (KEY side effects):

Drug	Side Effect
Tenofovir (TDF)	Nephrotoxicity, Fanconi syndrome, decreased bone density
Zidovudine (AZT)	Anemia, neutropenia, myopathy; mitochondrial toxicity
Abacavir (ABC)	Hypersensitivity reaction (HLA-B*5701 screening)
Efavirenz	Neuropsychiatric (vivid dreams, dizziness), avoid in pregnancy (1st trimester)
Nevirapine	Stevens-Johnson syndrome, hepatotoxicity
Lopinavir/Ritonavir	GI intolerance, lipodystrophy, QT prolongation
Raltegravir (Integrase inhibitor)	CPK elevation, rhabdomyolysis
Maraviroc (CCR5 antagonist)	Hepatotoxicity, test CCR5 tropism first

PYQ-type: "CD4 <200 + GGO on HRCT?" → PCP "Ring-enhancing brain lesion in HIV patient?" → Toxoplasmosis (multiple); Primary CNS lymphoma (solitary/single in later stages)

HEPATITIS VIRUSES ★★★

Buzzwords: HAV feco-oral, HBV ssDNA, HCV MCC chronic, HDV superinfection, HEV pregnant

Virus	Family	Genome	Route	Chronicity
HAV	Picornavirus	+ssRNA	Feco-oral	Never chronic
HBV	Hepadnavirus	Partially dsDNA (unique)	Parenteral/sexual/vertical	5-10% adults, 90% neonates
HCV	Flavivirus	+ssRNA	Parenteral	70-80% (highest chronicity)
HDV	Deltavirus	-ssRNA (circular, virusoid)	Parenteral (needs HBV)	Co-infection <5%, superinfection >70%
HEV	Hepevirus	+ssRNA	Feco-oral	Highest mortality in pregnancy (20-30%)

HBV Serology (CRITICAL TABLE):

Marker	Significance
HBsAg	Acute/chronic infection marker
Anti-HBs	Immunity (vaccine-induced OR recovery)
HBeAg	Active viral replication, high infectivity
Anti-HBe	Low infectivity (except pre-core mutant!)
Anti-HBc IgM	Acute HBV (also positive in window period!)
Anti-HBc IgG	Past infection or chronic infection
Window period	HBsAg -ve, Anti-HBs -ve, Anti-HBc IgM +ve
Core window	Anti-HBc is the ONLY positive marker

Pre-core mutant: HBeAg -ve but HBV DNA +ve (cannot make HBeAg but still replicates) HCV treatment: Direct Acting Antivirals (DAAs) - Sofosbuvir + Ledipasvir/Daclatasvir; >95% SVR

PYQ-type: "HBsAg -ve, Anti-HBs -ve, Anti-HBc IgM +ve?" → Window period of HBV "Hepatitis with highest mortality in pregnancy?" → HEV "Hepatitis that never becomes chronic?" → HAV

HERPES VIRUSES ★★★

Buzzwords: Latency, dsDNA, Multinucleated giant cells, Tzanck smear, Acyclovir

Virus	Disease	Latency Site
HSV-1	Oral herpes, encephalitis (temporal lobe), keratoconjunctivitis	Trigeminal ganglion
HSV-2	Genital herpes, neonatal herpes	Sacral ganglion
VZV	Chickenpox, Shingles (herpes zoster)	Dorsal root ganglion
EBV	Infectious mononucleosis, Burkitt's lymphoma, NPC, Hodgkin's lymphoma	B-lymphocytes
CMV	Congenital CMV (MCC congenital viral infection), retinitis in HIV, mono-like in immunocompetent	Monocytes/macrophages
HHV-6	Roseola infantum (exanthem subitum), 6th disease	T-lymphocytes
HHV-7	Roseola (some cases)	T-lymphocytes
HHV-8	Kaposi's sarcoma, PEL (primary effusion lymphoma)	B-lymphocytes/endothelial

EBV/Mono:

Monospot test = Paul-Bunnell test (heterophile antibodies, IgM)
Atypical lymphocytes (Downey cells)
Complications: Splenic rupture, airway obstruction, meningoencephalitis
Avoid ampicillin → causes maculopapular rash in EBV
Associated tumors: Burkitt's lymphoma (t(8;14), c-myc), NPC (nasopharyngeal carcinoma), Hodgkin's lymphoma

CMV congenital:

Periventricular calcifications (vs Toxo = diffuse calcifications)
Sensorineural hearing loss (MCC of congenital SNHL), chorioretinitis, microcephaly

PYQ-type: "Atypical lymphocytes, splenomegaly, positive monospot, avoid ampicillin?" → EBV mono "Periventricular calcifications in TORCH infection?" → CMV (vs toxo = diffuse/basal ganglia)

INFLUENZA VIRUS ★★★

Buzzwords: H and N antigens, Antigenic shift vs drift, Amantadine, Oseltamivir, Reassortment

Feature	Detail
Family	Orthomyxovirus
Genome	Segmented -ssRNA (8 segments for A & B)
Antigens	HA (Hemagglutinin) = attachment (fusion); NA (Neuraminidase) = release from cells
Antigenic drift	Point mutations in HA/NA → minor changes → seasonal epidemics
Antigenic shift	Reassortment of gene segments between different strains → major change → pandemics

Pandemic 2009 (H1N1): Reassortment of human + swine + avian strains Influenza A - causes pandemics (most important); infects humans, birds, pigs, horses Influenza B - only humans, milder, no pandemics Influenza C - no NA, mild upper respiratory

Treatment: Oseltamivir (Tamiflu) - neuraminidase inhibitor; start within 48 hrs Amantadine/Rimantadine - M2 protein blockers, only Influenza A, high resistance now

Complications: Pneumonia (primary viral or secondary bacterial S. aureus/Strep pneumo), Reye's syndrome (aspirin in children - AVOID), encephalitis

PYQ-type: "Pandemic influenza caused by?" → Antigenic shift (reassortment) "Mechanism of action of Oseltamivir?" → Neuraminidase inhibitor

RABIES VIRUS ★★★

Buzzwords: Negri bodies, Hydrophobia, Rhabdovirus, Post-exposure prophylaxis, Bullet-shaped

Feature	Detail
Family	Rhabdovirus
Morphology	Bullet-shaped (bacilliform)
Pathology	Negri bodies = eosinophilic cytoplasmic inclusions in Purkinje cells (cerebellum) and hippocampus (Ammon's horn)
Spread	Retrograde axonal transport to CNS

Post-exposure prophylaxis (PEP):

Category I (touching, licking intact skin) → Wash + No vaccine
Category II (nibbling, superficial scratch, no bleeding) → Wound wash + Vaccine only
Category III (transdermal bite, exposure to mucous membrane/saliva) → Wound wash + Vaccine + RIG (Rabies Immunoglobulin)

RIG: Human RIG (HRIG) or Equine RIG (ERIG) → infiltrate at wound site + IM at distant site (if remaining volume) Vaccine schedule: Days 0, 3, 7, 14, 28 (Essen) OR Days 0, 7, 21/28 (Zagreb 2-1-1)

Diagnosis of animal: Direct fluorescent antibody test (DFA) on brain tissue (gold standard)

PYQ-type: "Negri bodies in hippocampus/Purkinje cells?" → Rabies "Category III animal bite - management?" → Wound wash + Vaccine + RIG

SECTION 3: PARASITOLOGY

PLASMODIUM (MALARIA) ★★★

Buzzwords: Anopheles, Schuffner's dots, Quartan/Tertian fever, Blackwater fever, Primaquine liver stage

Species	Fever Cycle	RBC preference	Special features
P. vivax	Tertian (48 hrs)	Young/reticulocytes (enlarged)	Schuffner's dots, relapse (hypnozoites)
P. ovale	Tertian (48 hrs)	Young (enlarged, oval, fimbriated)	Relapse (hypnozoites), Schuffner's dots
P. malariae	Quartan (72 hrs)	Old/senescent (normal size)	Band/basket form trophozoites, "rosette" schizonts
P. falciparum	Malignant tertian (36-48 hrs)	All ages (most severe)	Maurer's clefts, ring forms only in peripheral blood, no enlargement

P. falciparum complications:

Cerebral malaria → ring hemorrhages, Dürck's granuloma
Blackwater fever → massive hemolysis → hemoglobinuria → dark urine → AKI
Hyperparasitemia (>5% RBCs parasitized)
Sequestration (rosetting + cytoadherence) → microvascular obstruction
ARDS, hypoglycemia (quinine → insulin release)

Diagnosis:

Thick blood smear = most sensitive (gold standard for low parasitemia)
Thin blood smear = species identification
RDT (rapid diagnostic test) = pLDH/HRP-2 antigens
QBC (Quantitative Buffy Coat) = acridine orange

Treatment:

Uncomplicated P. vivax/ovale: Chloroquine + Primaquine (for liver hypnozoites - prevent relapse; check G6PD first)
Uncomplicated P. falciparum: ACT (Artemisinin-based Combination Therapy) - Artemether-Lumefantrine (AL), Artesunate-Mefloquine
Severe malaria: IV Artesunate (DOC), or IV Quinine + Doxycycline
Primaquine: NEVER in G6PD deficiency or pregnancy

PYQ-type: "Quartan fever, band forms, rosette?" → P. malariae "Blackwater fever + hemoglobinuria?" → P. falciparum "Why give primaquine in P. vivax?" → Eradicate liver hypnozoites (radical cure)

ENTAMOEBA HISTOLYTICA ★★★

Buzzwords: Flask-shaped ulcer, RBC in trophozoite, Liver abscess anchovy sauce, Metronidazole

Feature	Detail
Key	RBC in trophozoite (PATHOGNOMONIC of E. histolytica vs E. dispar)
Ulcer	Flask-shaped (bottle-neck) ulcer in colon (undermined edges)
Liver abscess	Anchovy paste/chocolate sauce pus (= lysed blood + necrotic material, sterile)
Cyst	4 nuclei (mature), chromatoid bars with blunt ends
Serology	ELISA for anti-amoebic antibody (liver abscess)

Amoebic vs Pyogenic liver abscess:

Amoebic: Young male, single abscess (right lobe), "anchovy paste" pus, sterile, ELISA +ve → Treat with Metronidazole alone (no drainage usually needed)
Pyogenic: Elderly, multiple abscesses, pus culture +ve (E. coli, Klebsiella) → Antibiotics + drainage

Treatment: Metronidazole (tissue amoebicide) + Diloxanide furoate (luminal amoebicide, for cyst passers/after Metronidazole)

PYQ-type: "Trophozoite with ingested RBCs?" → E. histolytica "Sterile pus in liver abscess, right lobe, young male?" → Amoebic liver abscess

GIARDIA LAMBLIA ★★★

Buzzwords: Falling leaf motility, Sucking disc, Steatorrhea, Duodenal aspirate, Metronidazole

Trophozoite: Pear-shaped, bilateral symmetry (owl/ghost face), 2 nuclei, sucking disc (ventral)
Cyst: Oval, 4 nuclei
Motility: Falling leaf motility
Causes: Malabsorption/steatorrhea (flattening of villi, NOT invading)
Diagnosis: Stool microscopy (cysts), string test (Entero-test) for trophozoites, ELISA stool antigen
Treatment: Metronidazole or Tinidazole

TOXOPLASMA GONDII ★★★

Buzzwords: Definitive host = cat, Congenital toxo, Intracranial calcifications, Sabin-Feldman dye test, Pyrimethamine

Definitive host: Cat (only host where sexual cycle occurs)
Transmission: Undercooked meat (tissue cysts), cat feces (oocysts), vertical (congenital)
Congenital tetrad (Sabin's tetrad): Hydrocephalus + Chorioretinitis + Intracranial calcifications (diffuse, periventricular) + Psychomotor retardation
AIDS: CD4 <100, ring-enhancing brain lesions (toxoplasma encephalitis)
Diagnosis: Serology (IgM/IgG), Sabin-Feldman dye test (gold standard - but not done routinely), PCR
Treatment: Pyrimethamine + Sulfadiazine + Folinic acid (leucovorin)

vs CMV calcifications: Toxo = diffuse/basal ganglia, CMV = periventricular

LEISHMANIASIS ★★★

Buzzwords: Sandfly Phlebotomus, Aldehyde test, Splenomegaly, Amastigote, Napier's test

Type	Organism	Feature
Visceral (Kala-azar)	L. donovani	Splenomegaly > hepatomegaly, pancytopenia, hypergammaglobulinemia, blackening of skin
Cutaneous	L. tropica, L. major	Painless ulcer, Delhi boil
Mucocutaneous	L. braziliensis	Espundia, nose/mouth destruction
PKDL	L. donovani	Post-kala-azar dermal leishmaniasis (after treatment)

Tests:

Aldehyde test (Napier's formol gel test) → hypergammaglobulinemia → gelatin in formalin within 2 min = +ve (kala-azar)
Direct agglutination test (DAT) → sensitive and specific
rK39 dipstick → rapid field test (best for VL)
Bone marrow/spleen/LN aspirate → definitive (Leishman-Donovan bodies = amastigotes in macrophages)

Treatment: Liposomal Amphotericin B (DOC, India); Miltefosine (oral), Sodium stibogluconate (pentavalent antimony)

SECTION 4: MYCOLOGY

CANDIDA ★★★

Buzzwords: Pseudohyphae, Germ tube, Azoles, Thrush, Vaginal candidiasis, IELTS

Feature	Detail
Key test	Germ tube test = C. albicans (forms germ tubes in serum at 37°C within 2-3 hrs)
Morphology	Pseudohyphae + budding yeast cells
Chromogenic agar	Green colonies = C. albicans

Diseases: Oral thrush (HIV/immunosuppressed/infants), vulvovaginal candidiasis, esophageal candidiasis (AIDS-defining), candidemia (IVDA, TPN, broad-spectrum antibiotics), UTI (catheterized) Treatment: Fluconazole (oral/systemic, azole); Caspofungin (echinocandin, for Candida resistant to azoles); Nystatin (topical/oral thrush)

CRYPTOCOCCUS NEOFORMANS ★★★

Buzzwords: India ink, Latex agglutination, Mucoid capsule, Pigeon droppings, CD4 <100

Feature	Detail
Stain	India ink → clear halo (capsule appears as clear zone)
Test	Latex agglutination (capsular polysaccharide antigen = most sensitive, DOC for diagnosis)
Source	Pigeon droppings, soil
Capsule	Polysaccharide (main virulence)

Disease: Meningitis in HIV (CD4 <100), "soap bubble lesions" (gelatinous pseudocysts) in brain Treatment: Amphotericin B + Flucytosine (induction, 2 wks) → Fluconazole (consolidation + maintenance) CSF findings: Elevated opening pressure, lymphocytosis, decreased glucose, increased protein

ASPERGILLUS FUMIGATUS ★★★

Buzzwords: Septate hyphae, Dichotomous branching 45°, Fruiting head, Voriconazole, Galactomannan

Feature	Detail
Hyphae	Septate, branching at 45° (acute angle)
Fruiting head	Conidiophores with vesicle + phialides (sterigmata)
Aspergilloma	Fungus ball in pre-existing cavity (TB, sarcoid) → Monod sign (crescent/air-crescent sign on CT)

Diseases:

ABPA (Allergic bronchopulmonary aspergillosis) → Asthma + eosinophilia + central bronchiectasis + high IgE; Rx: Prednisolone + Itraconazole
Invasive aspergillosis → neutropenic patients (AML on chemotherapy), "Halo sign" (early) then "Air-crescent sign" (late) on CT chest; Voriconazole (DOC)
Aspergilloma → Hemoptysis, no treatment usually (unless hemoptysis), surgical if massive

Diagnosis: Galactomannan assay (serum/BAL) → screens for invasive aspergillosis; Beta-D-glucan (non-specific fungal marker)

PYQ-type: "Halo sign on CT chest in neutropenic patient?" → Invasive aspergillosis "Aspirin-shaped septate hyphae at 45°?" → Aspergillus

MUCOR/RHIZOPUS (MUCORMYCOSIS) ★★★

Buzzwords: Rhinocerebral, Diabetic ketoacidosis, Non-septate hyphae, 90° branching, Black eschar, Liposomal AmphoB

Feature	Detail
Hyphae	Non-septate (aseptate/coenocytic), branching at 90° (right angle)
Risk	DKA (most classic), neutropenia, iron overload (deferoxamine!), burns
Spread	Angioinvasive → thrombosis, infarction, tissue necrosis

Forms:

Rhinocerebral (most common overall) → DKA → black necrotic tissue in nose/palate/orbit → can spread to brain
Pulmonary → neutropenic patients (similar to Aspergillus)
GI → malnourished
Cutaneous → burns

Treatment: Liposomal Amphotericin B (DOC) + surgical debridement + control of underlying disease Deferoxamine paradox: Deferoxamine (iron chelator) provides iron to Mucor via ferrioxamine → INCREASES risk of mucormycosis

PYQ-type: "DKA patient with black nasal eschar, right-angle branching non-septate hyphae?" → Mucormycosis "Iron chelation therapy increasing risk of fungal infection?" → Deferoxamine + Mucormycosis

SECTION 5: IMMUNOLOGY (MICROBIOLOGY COMPONENT)

HYPERSENSITIVITY REACTIONS ★★★

Buzzwords: Gell-Coombs classification, Immediate, Cytotoxic, Immune complex, Delayed

Type	Mechanism	Mediator	Examples
Type I (Immediate)	IgE + Mast cell degranulation	Histamine, leukotrienes	Anaphylaxis, asthma, urticaria, food allergy
Type II (Cytotoxic)	IgG/IgM + complement → cell lysis	Complement, ADCC	Autoimmune hemolytic anemia, Goodpasture's, myasthenia gravis, Graves', transfusion reactions
Type III (Immune complex)	IgG immune complex deposition	Complement, neutrophils	SLE, PSGN, serum sickness, Farmer's lung, Arthus reaction
Type IV (Delayed/DTH)	T-cell mediated (CD4/CD8)	Cytokines (IL-2, IFN-γ), CTL	TB (PPD test), contact dermatitis, graft rejection

Serum sickness: Day 7-14, immune complexes, type III; fever + rash + arthralgia + lymphadenopathy Arthus reaction: Local type III (intradermal antigen in sensitized individual)

PRIMARY IMMUNODEFICIENCIES ★★★

Disease	Defect	Key Features
Bruton's X-linked agammaglobulinemia	BTK gene → no B cells, no Ig	Male, >6 months (maternal Ab wanes), recurrent bacterial infections (encapsulated), no tonsils
DiGeorge syndrome	22q11.2 deletion, thymus aplasia → no T cells	Cardiac defects (conotruncal), hypocalcemia (tetany), recurrent viral/fungal infections
SCID	Both B + T cell defects (ADA deficiency most common)	Profound infections with all pathogens, graft-vs-host from maternal lymphocytes
Hyper-IgM syndrome	CD40L/CD40 defect → no class switching	Very high IgM, no IgG/A/E, Pneumocystis, Cryptosporidium
CVID	Late onset, ↓ all Ig	Adults, recurrent bacterial infections, Giardia
Chediak-Higashi	LYST gene → giant granules, defective lysosome trafficking	Partial albinism, recurrent infections, giant granules in neutrophils
Chronic Granulomatous Disease (CGD)	NADPH oxidase defect → no oxidative burst	Recurrent catalase-positive organisms (S. aureus, Aspergillus, Nocardia, Serratia, Burkholderia), granuloma formation
C5-C9 deficiency	Terminal complement defect	Recurrent Neisseria (meningitidis + gonorrhoeae) infections
IgA deficiency	Most common primary immunodeficiency	Recurrent sinopulmonary infections, anaphylaxis with blood products (anti-IgA antibodies)

SECTION 6: HIGH-YIELD MNEMONICS & QUICK RECALL

BUZZWORD-DISEASE QUICK TABLE ★★★

Buzzword	Organism	Disease
Drumstick spore	C. tetani	Tetanus
Bamboo stick colony	B. anthracis	Anthrax
Chinese letter arrangement	C. diphtheriae	Diphtheria
Darting motility, rice water	V. cholerae	Cholera
Falling leaf motility	Giardia	Giardiasis
Negri bodies (Purkinje/hippocampus)	Rabies virus	Rabies
Germ tube in serum	C. albicans	Candidiasis
India ink halo	Cryptococcus	Cryptococcal meningitis
Non-septate hyphae 90°	Mucor/Rhizopus	Mucormycosis
Septate hyphae 45°	Aspergillus	Aspergillosis
Ziehl-Neelsen red bacilli	M. tuberculosis	Tuberculosis
Fite-Faraco stain	M. leprae	Leprosy
Leishman-Donovan bodies	Leishmania	Kala-azar
Schuffner's dots	P. vivax/ovale	Malaria
Maurer's clefts	P. falciparum	Falciparum malaria
RBCs ingested by trophozoite	E. histolytica	Amoebiasis
Owl-eye inclusion	CMV	CMV infection
Councilman bodies	Yellow fever	Yellow fever
Guarnieri bodies	Vaccinia/Smallpox	Poxvirus
Downey cells	EBV	Infectious mono
Warthin-Finkeldey cells	Measles	Measles
Cowdry type A inclusions	HSV/VZV	Herpetic infections

MEDIA CHEAT SHEET ★★★

Medium	Organism(s)
Chocolate agar	N. meningitidis, N. gonorrhoeae, H. influenzae
Thayer-Martin	N. gonorrhoeae (selective)
Mannitol salt agar	S. aureus (selective)
Bordet-Gengou	B. pertussis
TCBS (yellow colonies)	V. cholerae
TCBS (green colonies)	V. parahaemolyticus
Lowenstein-Jensen	M. tuberculosis
Skirrow's	H. pylori, Campylobacter
BCYE (Buffered Charcoal Yeast Extract)	Legionella pneumophila
Tellurite agar	C. diphtheriae (black colonies)
MacConkey (pink = lac+)	E. coli, Klebsiella
MacConkey (colorless = lac-)	Salmonella, Shigella, Pseudomonas
Charcoal blood agar (CBA)	Bordetella pertussis (alternative)
Sabouraud's agar	Fungi (most)

EXOTOXIN vs ENDOTOXIN ★★★

Feature	Exotoxin	Endotoxin (LPS)
Source	Gram +ve AND -ve	Gram -ve (outer membrane)
Chemistry	Protein	Lipid A (active component)
Heat	Labile (mostly)	Heat stable
Antigenicity	High (toxoid possible)	Low
Lethal dose	Very low	High
Superantigen	Some (TSST-1, SPE)	No

ANTIBIOTICS HIGH YIELD

Beta-lactams mechanism: Inhibit PBPs → block transpeptidation → cell wall synthesis failure → bactericidal Vancomycin: Inhibits transglycosylation (binds D-Ala-D-Ala precursor) Aminoglycosides: 30S ribosome → misreading of mRNA → bactericidal; nephrotoxic + ototoxic Macrolides: 50S ribosome → inhibit translocation → bacteriostatic Tetracyclines: 30S → block aminoacyl-tRNA binding → bacteriostatic Chloramphenicol: 50S → inhibit peptidyl transferase → Grey baby syndrome (no glucuronyl transferase in neonates) Fluoroquinolones: Inhibit DNA gyrase (gram -ve) + Topoisomerase IV (gram +ve) Rifampicin: Inhibits DNA-dependent RNA polymerase → bactericidal Metronidazole: Anaerobes + protozoa → free radicals → DNA damage

"30S = ATCM" mnemonic: Aminoglycosides, Tetracyclines, Chloramphenicol (actually 50S), Macrolides

📚 STUDY STRATEGY FOR MICROBIOLOGY (NEET PG <5000 Rank)

Priority topics (highest yield, based on exam trends):

Bacterial toxins - mechanism, disease, treatment (appears in every exam)
HIV/AIDS - staging, OIs, ART side effects
Tuberculosis - drugs, side effects, diagnosis
Serology (HBV markers, Widal, VDRL) - interpret scenarios
Media and stains - simple but reliable marks
Malaria - species differentiation, complications, drugs
Immunodeficiencies - match defect to organism
Antifungals - mechanism and spectrum

Revision technique:

For each organism: Organism → Unique feature → Disease → Investigation → Treatment
Use the trigger word (buzzword) tables for rapid MCQ solving
Practice: "If question says X → think Y organism"
Revise this sheet 3 times minimum before exam

Sources: Medical Microbiology 9e (Murray), Jawetz Melnick & Adelbergs Medical Microbiology 28e, Sherris & Ryan's Medical Microbiology 8e, Robbins Pathology, Harrison's Internal Medicine 22e

This covers the core of NEET PG Microbiology. Next subjects ready to cover: Pathology, Pharmacology, Physiology, Biochemistry, Anatomy, Surgery, Medicine, OBG, Pediatrics, Ophthalmology, ENT, Orthopedics, Psychiatry, Skin, Radiology, Anesthesia, Forensic Medicine, Community Medicine, Microbiology Done ✓

Type "next" or name the subject and I'll build the next high-yield revision sheet!

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