Microbiology in detail notes

Reading File

The query is quite broad - "Microbiology in detail notes" could cover many areas. Let me clarify before proceeding.

Asking for Preferences

Which area of microbiology do you want detailed notes on? · What level of detail are you targeting?

Searching sources...

Finding Sources

Reading File

Finding Sources

Reading File

Finding Sources

Here are your comprehensive USMLE-focused Bacteriology Notes, synthesized from Jawetz, Melnick & Adelberg's Medical Microbiology 28e, Henry's Clinical Diagnosis & Management, and Sherris & Ryan's Medical Microbiology 8e:

🦠 BACTERIOLOGY - Detailed USMLE Notes

SECTION 1: FUNDAMENTALS OF BACTERIA

1.1 Prokaryote vs. Eukaryote - Key Differences

Feature	Prokaryote (Bacteria)	Eukaryote (Human Cell)
Nuclear membrane	Absent	Present
Chromosome	Single circular, haploid	Multiple linear, diploid
Cell wall	Present (peptidoglycan)	Absent
Ribosomes	70S (30S + 50S)	80S (40S + 60S)
Size	~1 µm	10-100 µm
Mitochondria	Absent	Present
Introns	Rare (except Archaebacteria)	Common

High-Yield: Antibiotics targeting 70S ribosomes (aminoglycosides, macrolides, tetracyclines, chloramphenicol, linezolid) selectively kill bacteria without harming human 80S ribosomes.

1.2 Bacterial Cell Wall

Gram-Positive vs. Gram-Negative

Feature	Gram-Positive (+)	Gram-Negative (-)
Peptidoglycan layer	Thick (multilayer)	Thin (single layer)
Outer membrane	Absent	Present
LPS (endotoxin)	Absent	Present
Teichoic acid	Present	Absent
Periplasmic space	Narrow	Wide
Crystal violet stain	Purple	Red (decolorized)

Gram Stain Steps (mnemonic: "Crystal Violet Girls Are Pretty"):

Crystal Violet (primary stain) - all bacteria purple
Gram Iodine (mordant) - fixes crystal violet
Alcohol/Acetone (decolorizer) - washes out gram-negative
Safranin (counterstain) - gram-negatives turn red/pink

Gram-positive exceptions (don't stain well):

Mycobacteria - use Acid-Fast stain (Ziehl-Neelsen)
Mycoplasma - NO cell wall at all
Treponema - too thin, use dark-field microscopy
Chlamydia/Rickettsia - obligate intracellular

1.3 Special Bacterial Structures

Structure	Bacteria	Clinical Significance
Capsule	S. pneumoniae, H. influenzae, N. meningitidis, K. pneumoniae	Anti-phagocytic; polysaccharide = T-independent antigen
Endospore	Bacillus, Clostridium	Heat/chemical-resistant; autoclave at 121°C to kill
Flagella	E. coli, Salmonella, Vibrio	Motility; H antigen
Pili/Fimbriae	N. gonorrhoeae, E. coli	Adhesion, colonization
Biofilm	P. aeruginosa, S. epidermidis	Resistant to antibiotics; found on catheters

Mnemonic for encapsulated bacteria: "Some Killers Have Pretty Nice Capsules"

Streptococcus pneumoniae
Klebsiella pneumoniae
H. influenzae type b
Pseudomonas aeruginosa
Neisseria meningitidis
Cryptococcus neoformans (fungus, but same concept)

SECTION 2: BACTERIAL CLASSIFICATION

2.1 Gram-Positive Cocci

Organism	Key Features	Disease	Treatment
S. aureus	Coagulase+, catalase+, beta-hemolytic, golden colonies	Skin infections, osteomyelitis, endocarditis, toxic shock syndrome, food poisoning	Nafcillin (MSSA); Vancomycin (MRSA)
S. epidermidis	Coagulase-, novobiocin-sensitive	Prosthetic valve endocarditis, catheter infections	Vancomycin
S. saprophyticus	Coagulase-, novobiocin-resistant	UTI in young sexually active women	TMP-SMX
S. pneumoniae	Alpha-hemolytic, lancet-shaped diplococci, optochin-sensitive, bile-soluble	Pneumonia, meningitis, otitis media, sinusitis	Penicillin G (amoxicillin); ceftriaxone if resistant
S. pyogenes (GAS)	Beta-hemolytic, bacitracin-sensitive, PYR+	Strep throat, rheumatic fever, scarlet fever, necrotizing fasciitis	Penicillin
S. agalactiae (GBS)	Beta-hemolytic, bacitracin-resistant, CAMP test+	Neonatal meningitis/sepsis, postpartum endometritis	Ampicillin
Enterococcus	Grows in 6.5% NaCl, PYR+	UTI, endocarditis, biliary infection	VRE: Linezolid/Daptomycin

Viridans Streptococci (alpha-hemolytic, optochin-resistant):

S. mutans - dental caries
S. mitis/sanguis - subacute bacterial endocarditis (especially on damaged valves)

2.2 Gram-Negative Cocci

Organism	Key Features	Disease	Treatment
N. gonorrhoeae	Oxidase+, ferments glucose only, no polysaccharide capsule, no normal flora	Gonorrhea, PID, neonatal ophthalmia, septic arthritis	Ceftriaxone + azithromycin
N. meningitidis	Oxidase+, ferments glucose AND maltose, has capsule	Meningococcal meningitis, Waterhouse-Friderichsen syndrome	Penicillin G; prophylaxis: rifampin/ciprofloxacin
Moraxella catarrhalis	Oxidase+, beta-lactamase producer	Otitis media, sinusitis, COPD exacerbations	Amoxicillin-clavulanate

2.3 Gram-Positive Rods (Bacilli)

Organism	Spore?	Key Features	Disease
B. anthracis	Yes	Non-motile, "Medusa head" colonies, anthrax toxin	Cutaneous anthrax (malignant pustule), inhalation anthrax (woolsorter's disease)
B. cereus	Yes	Motile	Food poisoning (reheated rice = preformed toxin; nausea 1-5h)
C. difficile	Yes	Pseudomembranous colitis, toxin A+B	Colitis post-antibiotics; treat with vancomycin PO or fidaxomicin
C. perfringens	Yes	Gas gangrene (lecithinase/alpha toxin), food poisoning (spores survive cooking)	Gas gangrene, food poisoning
C. tetani	Yes	Terminal spores (drumstick appearance), tetanospasmin (blocks GABA/glycine)	Tetanus (spastic paralysis, trismus)
C. botulinum	Yes	Preformed toxin, blocks ACh release at NMJ	Botulism (flaccid paralysis, descending)
Listeria monocytogenes	No	Tumbling motility, grows at 4°C (cold-enrichment), CAMP+, intracellular	Neonatal meningitis, septicemia in pregnancy, listeriosis in immunocompromised
Corynebacterium diphtheriae	No	Club-shaped, metachromatic granules, Loeffler/tellurite media	Diphtheria (pseudomembrane, myocarditis, neuropathy)
Actinomyces israelii	No	Anaerobic, branching, sulfur granules in pus	Cervicofacial actinomycosis ("lumpy jaw")
Nocardia	No	Aerobic, partially acid-fast, branching	Pulmonary infection in immunocompromised; brain abscess

C. tetani vs. C. botulinum:

Tetanus: ascending spastic paralysis, toxin travels retrograde via neurons
Botulism: descending flaccid paralysis, blocks presynaptic ACh release

2.4 Gram-Negative Rods - Enterobacteriaceae

Family features: Oxidase-negative, ferment glucose, reduce nitrates, facultative anaerobes

Organism	Key Tests	Disease	Treatment
E. coli	Indole+, MUG+, lactose fermenter	UTI (#1 cause), neonatal meningitis (K1 antigen), traveler's diarrhea (ETEC), EHEC O157:H7 (HUS), neonatal sepsis	Fluoroquinolones (UTI); ceftriaxone (meningitis)
Klebsiella pneumoniae	Urease+, lactose+, capsule	"Currant jelly" sputum pneumonia, UTI, nosocomial infections	Ceftriaxone; carbapenems for ESBL
Proteus mirabilis	Urease+, swarming motility, struvite stones	UTI, struvite (staghorn) kidney stones	Fluoroquinolones; TMP-SMX
Salmonella	H2S+, no lactose, motile	Typhoid fever (S. typhi), gastroenteritis (non-typhi), septicemia in sickle cell	Ciprofloxacin/ceftriaxone (typhi); supportive (non-typhi)
Shigella	No H2S, no lactose, non-motile, no gas	Dysentery (bloody diarrhea), HUS (S. dysenteriae), very low infective dose (10 organisms)	Ciprofloxacin or ceftriaxone (severe); self-limited otherwise
Yersinia enterocolitica	Oxidase-, cold-tolerant	Bloody diarrhea, pseudo-appendicitis (mesenteric lymphadenitis), reactive arthritis	Fluoroquinolones for severe cases
H. influenzae	Requires factors X (hemin) and V (NAD), "satellite phenomenon"	Epiglottitis (type b), meningitis (children), otitis media, sinusitis	Ceftriaxone; prophylaxis: rifampin

Mnemonic for Lactose Fermenters (pink on MacConkey): "CEEK"

Citrobacter
Enterobacter
E. coli
Klebsiella

Non-Lactose Fermenters (colorless on MacConkey):

Shigella, Salmonella, Proteus, Pseudomonas, Yersinia

2.5 Gram-Negative Rods - Non-Enterobacteriaceae

Organism	Key Features	Disease	Treatment
Pseudomonas aeruginosa	Oxidase+, non-fermenter, blue-green pigment (pyocyanin), grape odor, aerobic	Burn/wound infections, pneumonia in CF patients, hot tub folliculitis, malignant otitis externa	Antipseudomonal beta-lactam + aminoglycoside
Haemophilus ducreyi	Requires factor X only	Chancroid (painful genital ulcer, painful inguinal lymphadenopathy)	Azithromycin or ceftriaxone
Bordetella pertussis	Bordet-Gengou agar, filamentous hemagglutinin + pertussis toxin	Whooping cough (catarrhal -> paroxysmal -> convalescent phase)	Azithromycin/erythromycin; vaccine (DTaP)
Legionella pneumophila	Silver stain, charcoal yeast extract agar with L-cysteine and iron, gram stain often negative clinically	Legionnaires' disease (severe atypical pneumonia), Pontiac fever	Azithromycin or fluoroquinolone
Helicobacter pylori	Urease+, oxidase+, catalase+, corkscrew motility	Peptic ulcer disease (>95% duodenal), gastric carcinoma, MALToma	Triple therapy: PPI + clarithromycin + amoxicillin
Brucella	Intracellular, undulant fever	Brucellosis (undulant fever, from unpasteurized dairy, animal contact)	Doxycycline + rifampin
Francisella tularensis	Tick or rabbit contact	Tularemia (ulceroglandular, pneumonic)	Streptomycin/gentamicin
Vibrio cholerae	Comma-shaped, oxidase+, rice-water diarrhea, cholera toxin (↑cAMP)	Cholera (profuse watery diarrhea, "rice-water stool")	Oral rehydration; doxycycline
Campylobacter jejuni	Oxidase+, grows at 42°C, comma/S-shaped	#1 cause of bacterial gastroenteritis in USA; bloody diarrhea; precedes Guillain-Barre syndrome	Azithromycin/fluoroquinolone

2.6 Anaerobes

Organism	Features	Disease	Treatment
Bacteroides fragilis	Capsule, polysaccharide, most common gut anaerobe	Intra-abdominal abscesses, peritonitis	Metronidazole; beta-lactam/beta-lactamase inhibitors
Fusobacterium	Spindle-shaped	Lemierre syndrome (septic jugular thrombophlebitis)	Metronidazole
Prevotella	Part of oral flora	Aspiration pneumonia, dental abscesses	Metronidazole + amoxicillin

SECTION 3: ATYPICAL BACTERIA

3.1 Obligate Intracellular Bacteria

Organism	Vector/Transmission	Disease	Test	Treatment
Rickettsia rickettsii	Tick	Rocky Mountain Spotted Fever (petechial rash: wrists/ankles -> trunk, fever, headache)	Weil-Felix reaction; immunofluorescence	Doxycycline
Rickettsia prowazekii	Body louse	Epidemic typhus	Weil-Felix	Doxycycline
Chlamydia trachomatis	STI/contact	Serovars A-C: trachoma (blindness); D-K: urethritis, PID, neonatal conjunctivitis; L1-L3: lymphogranuloma venereum	NAAT	Azithromycin (single dose) or doxycycline
C. pneumoniae	Respiratory droplets	Atypical pneumonia	Serology	Azithromycin
Coxiella burnetii	Aerosol from cattle/sheep	Q fever (no rash, no vector, spore-like forms in environment)	Serology	Doxycycline
Ehrlichia	Tick	Ehrlichiosis (fever, leukopenia, thrombocytopenia)	Morulae in monocytes	Doxycycline
Anaplasma	Tick (Ixodes)	Anaplasmosis (fever, leukopenia)	Morulae in granulocytes	Doxycycline

3.2 Mycobacteria (Acid-Fast Organisms)

Organism	Features	Disease	Treatment
M. tuberculosis	Cord factor (virulence), Ghon complex (primary), caseating granulomas	TB (pulmonary, miliary, meningitis, Pott disease of spine)	RIPE: Rifampin + Isoniazid + Pyrazinamide + Ethambutol
M. leprae	Cannot culture in vitro, grows in armadillos, grows at cooler temperatures	Leprosy: Tuberculoid (paucibacillary, cell-mediated) vs. Lepromatous (multibacillary, humoral)	Dapsone + rifampin (tuberculoid); add clofazimine (lepromatous)
M. avium complex (MAC)	Disseminated in AIDS (CD4 <50)	Fever, weight loss, night sweats, diarrhea	Clarithromycin + ethambutol
M. marinum	Aquatic (fish tanks/swimming pools)	Skin granulomas	Minocycline or clarithromycin
M. scrofulaceum	Cervical lymphadenopathy in children	Scrofula	Surgical excision

TB Drug Side Effects (USMLE classic):

Drug	Side Effect
Rifampin	Red/orange body fluids, hepatotoxicity, CYP inducer
Isoniazid	Peripheral neuropathy (B6 deficiency), hepatotoxicity, SLE-like
Pyrazinamide	Hyperuricemia (gout), hepatotoxicity
Ethambutol	Optic neuritis (red-green color blindness), retrobulbar neuritis

3.3 Mycoplasma

Organism	Features	Disease	Treatment
M. pneumoniae	No cell wall, smallest free-living bacterium, "walking pneumonia", cold agglutinins (IgM)	Atypical (walking) pneumonia - bilateral interstitial infiltrates, mild symptoms	Azithromycin or doxycycline (NOT beta-lactams)
M. hominis/U. urealyticum	Urease positive	Urethritis, PID	Doxycycline

High-Yield: Mycoplasma lacks a cell wall - beta-lactams (penicillins, cephalosporins) are completely ineffective.

3.4 Spirochetes

Organism	Disease	Key Features	Treatment
Treponema pallidum	Syphilis	Primary: painless chancre; Secondary: maculopapular rash (palms/soles), condylomata lata, fever; Tertiary: gummas, aortitis, tabes dorsalis; Congenital: saddle nose, Hutchinson teeth	Penicillin G (all stages)
Borrelia burgdorferi	Lyme disease	Stage 1: Erythema migrans (bull's-eye); Stage 2: Bell palsy, AV block, migratory arthritis; Stage 3: Chronic arthritis, encephalopathy	Doxycycline (early); ceftriaxone (late/neuro)
Leptospira interrogans	Leptospirosis	Animal urine (rats); biphasic: flu-like then Weil disease (jaundice, renal failure, hemorrhage)	Penicillin G or doxycycline

Syphilis Serology:

Non-treponemal tests (screening): VDRL, RPR - can have false positives (SLE, pregnancy, drug use)
Treponemal tests (confirmatory): FTA-ABS, TPPA - specific

SECTION 4: BACTERIAL PATHOGENESIS & VIRULENCE

4.1 Toxins

Exotoxins vs. Endotoxin:

Feature	Exotoxin	Endotoxin (LPS)
Source	Gram+ and Gram- bacteria, secreted	Gram- outer membrane, released on lysis
Chemistry	Protein	Lipopolysaccharide (lipid A is toxic)
Heat stability	Labile (except staph food poisoning)	Stable
Toxoid vaccine	Yes (tetanus, diphtheria)	No
Potency	Very high	Moderate
Fever production	Variable	Yes (strong pyrogenic via IL-1, IL-6, TNF)

Key Exotoxin Mechanisms:

Toxin	Organism	Mechanism
Cholera toxin	V. cholerae	ADP-ribosylates Gs → ↑cAMP → Cl-/water secretion
Pertussis toxin	B. pertussis	ADP-ribosylates Gi → ↑cAMP → impairs immune cell signaling
Diphtheria toxin	C. diphtheriae	ADP-ribosylates EF-2 → blocks protein synthesis
Anthrax toxin	B. anthracis	Edema factor (↑cAMP), Lethal factor (MAPK protease)
TSST-1	S. aureus	Superantigen - non-specific MHC II binding → massive cytokine release
Exfoliative toxin	S. aureus	Serine protease, cleaves desmoglein-1 → SSSS
Shiga toxin	S. dysenteriae / EHEC	Inactivates 60S ribosome → cell death → HUS
Tetanus toxin	C. tetani	Blocks GABA/glycine release in spinal inhibitory interneurons → spastic paralysis
Botulinum toxin	C. botulinum	Cleaves SNARE proteins → blocks ACh vesicle release → flaccid paralysis

Mnemonic - ADP-ribosylating toxins: "ABCDE"

Anthrax (EF), Bordetella pertussis, Cholera, Diphtheria, E. coli (ETEC - LT toxin like cholera)

4.2 Virulence Factors

Factor	Example	Function
Capsule	S. pneumoniae	Inhibits phagocytosis; T-independent antigen
Protein A	S. aureus	Binds Fc region of IgG → inhibits opsonization
IgA protease	S. pneumoniae, N. meningitidis, H. influenzae	Cleaves secretory IgA on mucous membranes
M protein	S. pyogenes	Anti-phagocytic, mimics host proteins → molecular mimicry → rheumatic fever
Coagulase	S. aureus	Fibrin clot formation → abscess formation
Leukocidin	S. aureus, P. aeruginosa	Kills WBCs
Collagenase	C. perfringens	Tissue destruction in gas gangrene
Adhesins/Pili	N. gonorrhoeae	Attachment to urogenital epithelium

SECTION 5: ANTIBIOTIC MECHANISMS & RESISTANCE

5.1 Antibiotic Classification by Mechanism

Mechanism	Antibiotics
Cell wall synthesis inhibition	Beta-lactams (penicillins, cephalosporins, carbapenems, monobactams), Vancomycin (glycopeptide - inhibits transpeptidation via D-Ala-D-Ala binding)
30S ribosome inhibition	Aminoglycosides (bactericidal), Tetracyclines (bacteriostatic)
50S ribosome inhibition	Chloramphenicol, Macrolides (azithromycin, erythromycin), Linezolid, Clindamycin
DNA gyrase / Topoisomerase II/IV	Fluoroquinolones
RNA polymerase	Rifampin
Cell membrane disruption	Polymyxins (B and E/colistin), Daptomycin (gram-positive only)
Folic acid synthesis	Sulfonamides (inhibit PABA utilization), TMP (inhibits dihydrofolate reductase)

Mnemonic for 50S inhibitors: "Buy AT 50, CLean"

B-nothing / Azithromycin / Tetracycline (actually 30S - keep for contrast) / Chloramphenicol / Linezolid / Clindamycin

5.2 Resistance Mechanisms

Mechanism	Example
Beta-lactamase production	S. aureus (penicillinase), ESBL gram-negatives
Altered PBPs (penicillin-binding proteins)	MRSA (mecA gene - PBP2a has low affinity for beta-lactams)
Efflux pumps	P. aeruginosa, tetracycline resistance
Modified ribosomal target	Vancomycin-resistant Enterococcus (VRE) - D-Ala-D-Ala changed to D-Ala-D-Lac
Enzymatic inactivation	Aminoglycoside-modifying enzymes (acetylation, phosphorylation)
Reduced permeability	P. aeruginosa (porin changes)

SECTION 6: HIGH-YIELD CLINICAL ASSOCIATIONS

6.1 Disease-Bug Associations (High Yield)

Clinical Scenario	Organism
UTI in young woman	E. coli
UTI in young sexually active woman (recurrent)	S. saprophyticus
Neonatal meningitis	E. coli (K1), S. agalactiae (GBS), Listeria
Meningitis in adults	S. pneumoniae, N. meningitidis
Meningitis in elderly/immunocompromised	Listeria monocytogenes
Septic arthritis in young adults	N. gonorrhoeae
Septic arthritis in children	S. aureus
Pneumonia in alcoholic	K. pneumoniae, S. pneumoniae
Pneumonia in cystic fibrosis	P. aeruginosa, S. aureus, Burkholderia cepacia
Pneumonia with diarrhea + hyponatremia	Legionella pneumophila
"Walking pneumonia" in young adult	Mycoplasma pneumoniae
Traveler's diarrhea	ETEC (E. coli)
Bloody diarrhea after hamburger	EHEC O157:H7
Bloody diarrhea, pseudo-appendicitis	Yersinia enterocolitica
Ascending cholangitis (Charcot's triad)	E. coli, Enterococcus, Klebsiella
Endocarditis - IV drug user	S. aureus (tricuspid valve)
Endocarditis - dental procedure	Viridans streptococci
Wound infection after surgery/trauma	C. perfringens (gas gangrene), S. aureus
Bite wound infection (human)	Eikenella corrodens
Bite wound infection (dog/cat)	Pasteurella multocida
Cat scratch disease	Bartonella henselae

6.2 Special Culture Media

Media	Organism Isolated
Blood agar	General purpose; see hemolysis patterns
MacConkey	Gram-negatives; differentiates lactose fermenters
Chocolate agar	H. influenzae, N. gonorrhoeae
Thayer-Martin (VCN)	Neisseria species
Charcoal-yeast extract + L-cysteine/iron	Legionella
Bordet-Gengou	Bordetella pertussis
Löffler's / Tellurite	C. diphtheriae
Lowenstein-Jensen	Mycobacterium tuberculosis
TCBS (thiosulfate-citrate-bile salt-sucrose)	Vibrio cholerae
Buffered charcoal yeast extract (BCYE)	Legionella
Regan-Lowe	B. pertussis

6.3 Special Stains

Stain	Organisms
Gram stain	Most bacteria
Ziehl-Neelsen (acid-fast)	Mycobacteria, Nocardia (partially)
India ink	Cryptococcus neoformans (fungus, but commonly tested with bacteria)
Silver stain (Warthin-Starry)	Legionella, H. pylori, Treponema
PAS (Periodic Acid-Schiff)	Tropheryma whipplei (Whipple disease)
Giemsa	Rickettsia, Borrelia, Plasmodium, Trypanosoma
Dark-field microscopy	Treponema pallidum

6.4 Toxin-Mediated Diseases - Quick Table

Disease	Toxin	Key Feature
Toxic shock syndrome (TSS)	TSST-1 (S. aureus) or Strep pyrogenic exotoxin	Superantigen, multiorgan failure, hypotension
Scalded skin syndrome (SSSS)	Exfoliative toxin (S. aureus)	Nikolsky sign+, superficial blisters
Diphtheria	Diphtheria toxin (encoded by beta-phage)	Pseudomembrane, myocarditis, neuropathy
Botulism	Botulinum toxin (serotypes A,B,E most common)	Descending flaccid paralysis, diplopia, dysphagia
Tetanus	Tetanospasmin	Ascending spastic paralysis, lockjaw
HUS	Shiga toxin	EHEC O157:H7 or S. dysenteriae; triad: microangiopathic hemolytic anemia + thrombocytopenia + renal failure
Cholera	Cholera toxin (↑cAMP)	Rice-water diarrhea, no fever, no WBCs in stool

SECTION 7: GENETICS & RESISTANCE TRANSFER

7.1 Methods of Genetic Transfer

Method	Description	Example
Transformation	Uptake of naked DNA from environment	S. pneumoniae (Griffith's experiment)
Transduction	DNA transferred via bacteriophage	S. aureus exotoxins (TSST-1, exfoliative), C. botulinum toxin, C. diphtheriae toxin
Conjugation	Direct cell-to-cell plasmid transfer via pilus (F pilus)	Gram-negative bacteria; spread of antibiotic resistance plasmids
Transposition	Movement of DNA segments (transposons) within/between genomes	Resistance genes jumping between plasmids

Toxins encoded by phages (bacteriophages) - mnemonic: "ABCDE Toxins"

Anthrax (no, this is chromosome/plasmid)
Botulinum toxin
Cholera toxin
Diphtheria toxin
Erythrogenic toxin of S. pyogenes (Scarlet fever)
Also: Shiga-like toxin of EHEC

SECTION 8: NORMAL FLORA & DISRUPTION

Site	Dominant Organisms
Skin	S. epidermidis, Propionibacterium acnes, Corynebacteria
Oropharynx	Viridans streptococci, Neisseria, H. influenzae
Colon	Bacteroides fragilis (most common), E. coli, Enterococcus
Vagina	Lactobacillus (produces lactic acid, maintains low pH)
Urethra	S. epidermidis, corynebacteria

Clinical Relevance:

Disruption of colonic flora (antibiotics) → C. difficile overgrowth → pseudomembranous colitis
Disruption of vaginal flora (antibiotics/pH change) → Candida overgrowth or bacterial vaginosis (Gardnerella)

QUICK REVIEW MNEMONICS

Bugs that do NOT gram stain well (need special stains):

"These Rascals May Micro-Copulate Lovingly"

Treponema (dark-field)
Rickettsia (Giemsa)
Mycobacteria (Ziehl-Neelsen)
Mycoplasma (no cell wall)
Chlamydia (intracellular)
Legionella (silver stain)

Bugs transmitted by ticks:

"Rocky Bouncin' Lyme ERA"

Rickettsia rickettsii (RMSF)
Borrelia burgdorferi (Lyme)
Lyme (Borrelia)
Ehrlichia
Anaplasma

Antibiotics to AVOID in pregnancy:

"SAFE Moms Take Really Good Care" (drugs that are SAFE vs. AVOID)

AVOID: Tetracyclines (teeth/bones), Fluoroquinolones (cartilage), Sulfonamides (neonatal jaundice, G3P trimester), Metronidazole (1st trimester), Aminoglycosides (fetal ototoxicity), Chloramphenicol (gray baby syndrome)

Sources: Jawetz, Melnick & Adelberg's Medical Microbiology 28e; Henry's Clinical Diagnosis & Management by Laboratory Methods; Sherris & Ryan's Medical Microbiology 8eThese are your complete Bacteriology Notes for USMLE preparation. Here's what's covered:

What's in these notes:

Fundamentals - Prokaryote structure, cell wall, Gram stain technique and interpretation
Gram-Positive Cocci - Staph, Strep, Enterococcus with key differentiating tests
Gram-Positive Rods - Spore-formers (Bacillus/Clostridium), non-spore-formers (Listeria, Diphtheria, Nocardia, Actinomyces)
Gram-Negative Rods - Enterobacteriaceae (E. coli, Salmonella, Shigella, Klebsiella) + non-Enterobacteriaceae (Pseudomonas, Legionella, H. pylori, Vibrio, Campylobacter)
Atypical Bacteria - Obligate intracellulars (Rickettsia, Chlamydia, Coxiella), Mycobacteria (TB, leprosy, MAC), Mycoplasma, Spirochetes (Syphilis, Lyme, Leptospira)
Pathogenesis - Exotoxins vs. endotoxin, virulence factors, toxin mechanisms
Antibiotics - Mechanism of action by class, resistance mechanisms
Clinical Correlations - High-yield bug-disease associations, special media, special stains
Genetics - Transformation, transduction, conjugation, phage-encoded toxins
Mnemonics throughout for fast retention

Let me know if you want me to go deeper on any specific section (e.g., TB treatment details, antibiotic resistance, Salmonella/Shigella comparison, or a specific organism for viva/exam prep).

This is a shared conversation. Sign in to Orris to start your own chat.