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Applied Microbiology & Infection Control - BSc Nursing 3rd Semester Notes

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SECTION A: APPLIED MICROBIOLOGY

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UNIT I - Introduction to Microbiology

What is Microbiology?

Importance in Nursing

• Understanding how pathogens cause disease
• Rational use of antibiotics and antiseptics
• Safe handling of specimens and sharps
• Infection prevention in clinical settings
• Understanding how vaccines work

Historical Milestones

Key Terminology

• Microorganism: Living organism invisible to the naked eye
• Pathogen: A microorganism capable of causing disease
• Saprophyte: Organism that lives on dead/decaying matter
• Commensal: Organism living on/in a host without harm or benefit
• Virulence: Degree of pathogenicity of an organism
• Infection: Invasion and multiplication of microorganisms in body tissues
• Colonization: Microorganisms present but not causing disease

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UNIT II - General Characteristics of Microbes

Classification of Microorganisms

1. Bacteria - Prokaryotes; no true nucleus
2. Viruses - Non-cellular; obligate intracellular parasites
3. Fungi - Eukaryotes; yeasts and moulds
4. Protozoa - Single-celled eukaryotes; e.g., Plasmodium, Amoeba
5. Helminths (worms) - Multicellular parasites
6. Prions - Misfolded proteins; e.g., Creutzfeldt-Jakob disease

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A. BACTERIA

Structure

Gram Staining (Most Important Lab Test)

Bacterial Morphology

Bacterial Growth Requirements

• Nutrients: Carbon, nitrogen, minerals, vitamins
• Temperature: Most pathogens grow at 37°C (body temperature)
  • Psychrophiles: 0-20°C
  • Mesophiles: 20-45°C (most pathogens)
  • Thermophiles: 45-80°C
• Moisture: Essential for growth (spores survive dryness)
• pH: Most pathogens prefer neutral pH (7.0-7.4)
• Oxygen:
  • Aerobic: Need oxygen (e.g., Mycobacterium TB)
  • Anaerobic: No oxygen (e.g., Clostridium)
  • Facultative anaerobe: Can survive with/without oxygen (e.g., E. coli)

Bacterial Growth Curve (4 phases)

1. Lag phase - Bacteria adjust to new environment; no multiplication
2. Log/Exponential phase - Rapid multiplication; most vulnerable to antibiotics
3. Stationary phase - Growth = death rate; nutrients depleted
4. Decline/Death phase - Death rate exceeds growth rate

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B. VIRUSES

Structure

• Non-cellular; range in size 20-300 nm
• Core: Nucleic acid (either DNA or RNA, never both)
• Coat: Capsid (protein shell)
• Some have a lipid envelope derived from host cell membrane (e.g., HIV, Influenza)
  • Enveloped viruses are more susceptible to disinfectants
  • Non-enveloped viruses (e.g., Hepatitis A, Norovirus) are more resistant

Viral Replication Cycle

1. Adsorption - Virus attaches to specific host receptor
2. Penetration - Virus enters host cell
3. Uncoating - Viral coat removed; nucleic acid released
4. Replication - New viral components synthesized using host machinery
5. Assembly - New virions assembled
6. Release - Virions released (by lysis or budding)

Important Pathogenic Viruses (Nursing Relevance)

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C. FUNGI

• Eukaryotic organisms; cell walls contain chitin
• Two forms: Yeasts (unicellular) and Moulds (multicellular, produce hyphae and spores)
• Dimorphic fungi: exist as both forms (e.g., Histoplasma)
• Most fungal infections are opportunistic (occur in immunocompromised patients)

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D. PROTOZOA

• Single-celled eukaryotes; transmitted by vectors, contaminated food/water, or sexual contact

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UNIT III - Pathogenesis of Infectious Disease

Chain of Infection

Infectious Agent → Reservoir → Portal of Exit → Mode of Transmission → Portal of Entry → Susceptible Host

Routes of Transmission

Virulence Factors (How Bacteria Cause Disease)

• Capsule - Resists phagocytosis (e.g., Pneumococcus)
• Adhesins/Pili - Attachment to host cells
• Toxins:
  • Endotoxin: Lipopolysaccharide (LPS) in Gram-negative cell wall; causes fever, shock
  • Exotoxin: Secreted proteins; highly specific (e.g., Botulinum toxin, Cholera toxin, Tetanus toxin)
• Enzymes - Hyaluronidase (tissue spread), coagulase (Staph aureus), streptokinase
• Intracellular survival - e.g., Mycobacterium TB survives inside macrophages

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UNIT IV - Immunity

Types of Immunity

Innate (Non-specific) Immunity - First line of defense

• Intact skin
• Mucous membranes
• Cilia (respiratory tract)
• Stomach acid (pH 1.5-2.5)

• Phagocytes (neutrophils, macrophages) - engulf and destroy pathogens
• Natural Killer (NK) cells - destroy virus-infected and tumour cells
• Complement system - cascade of proteins that lyse bacteria
• Fever - elevated temperature slows bacterial growth
• Interferons - antiviral proteins released by infected cells
• Inflammation - redness, heat, swelling, pain; localizes and limits infection

Adaptive (Specific) Immunity - Second line of defense

• Activated when innate immunity is overwhelmed
• Has memory - faster response on re-exposure (basis of vaccines)

Types of Acquired Immunity

Vaccines

• Live attenuated: Weakened live organism; stronger, longer immunity; e.g., BCG, MMR, OPV
• Killed/Inactivated: Dead organisms; safer; may need boosters; e.g., IPV, Hepatitis A
• Toxoid: Inactivated toxin; e.g., Tetanus toxoid, Diphtheria toxoid
• Subunit/Recombinant: Specific antigen components; e.g., Hepatitis B vaccine
• mRNA vaccines: e.g., COVID-19 vaccines (Pfizer, Moderna)

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UNIT V - Antimicrobial Agents & Antibiotic Stewardship

Classification of Antibiotics by Mechanism

Antibiotic Resistance

• Beta-lactamase production (breaks penicillin ring)
• MRSA - Methicillin-Resistant Staphylococcus aureus
• ESBL - Extended Spectrum Beta-Lactamase producing organisms
• VRE - Vancomycin-Resistant Enterococcus

Antibiotic Stewardship - Nurse's Role

• Administer antibiotics on time (maintain steady blood levels)
• Complete the full prescribed course
• Do not administer antibiotics without a culture/prescription
• Educate patients not to self-medicate or share antibiotics
• Monitor for side effects (allergy, C. difficile diarrhoea)
• Encourage culture and sensitivity testing before initiating therapy

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UNIT VI - Laboratory Methods in Microbiology

Specimen Collection (Nursing Role)

• Collect before starting antibiotic therapy whenever possible
• Use sterile containers
• Label correctly with patient name, ID, time, date, specimen type
• Transport promptly at correct temperature

Common Lab Tests

• Gram stain - Rapid identification of bacteria
• Culture and sensitivity (C&S) - Identifies organism and antibiotic sensitivity
• Ziehl-Neelsen (ZN) stain - Acid-fast bacteria (TB, Leprosy)
• India ink - Cryptococcus (capsule appears as halo)
• ELISA - Antibody/antigen detection (HIV, HBV)
• PCR - Molecular detection; very sensitive (COVID-19, TB)
• Microscopy - Wet mount for parasites/fungi

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SECTION B: INFECTION CONTROL & SAFETY

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UNIT VII - Sterilization & Disinfection

Key Definitions

• Sterilization: Complete destruction/removal of ALL living organisms including spores - an absolute term (Sherris & Ryan's Medical Microbiology, p. 100)
• Disinfection: Destruction of most pathogenic organisms - spores may survive (Sherris & Ryan's Medical Microbiology, p. 100)
• Antisepsis: Use of disinfecting agents on living tissue/skin
• Asepsis: System of practices to prevent microorganisms reaching a protected environment
• Pasteurization: Heat treatment sufficient to kill most pathogens but not spores (milk: 74°C for 3-5 seconds, or 62°C for 30 minutes)
• Sanitization: Reduction of microbial load to safe levels (used in food/housekeeping contexts)

Methods of Sterilization

Physical Methods

Chemical Agents

• High-level: Kills all organisms except high numbers of spores (for semi-critical items: endoscopes)
• Intermediate-level: Kills mycobacteria, most viruses and bacteria, some spores
• Low-level: Kills most bacteria and some viruses; not mycobacteria or spores (non-critical items)

Spaulding Classification (for selecting sterilization level)

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UNIT VIII - Hospital Acquired Infections (HAI) / Nosocomial Infections

Definition

Common Types of HAI

Risk Factors

• Invasive devices (IV lines, urinary catheters, ventilators)
• Surgical wounds
• Immunocompromised state (HIV, cancer, steroids)
• Extremes of age (newborns, elderly)
• Prolonged hospitalization
• Indiscriminate antibiotic use

Prevention of HAI - NURSE'S KEY ROLE

Standard Precautions (for ALL patients, ALL settings)

1. Hand hygiene - most effective single measure
2. Personal Protective Equipment (PPE) - gloves, mask, gown, goggles
3. Safe injection practices - one needle/syringe per patient
4. Respiratory hygiene/cough etiquette
5. Safe handling of sharps - never recap, use sharps bins
6. Environmental cleaning - regular disinfection of surfaces
7. Linen and waste management

WHO 5 Moments of Hand Hygiene

1. Before touching a patient
2. Before a clean/aseptic procedure
3. After body fluid exposure risk
4. After touching a patient
5. After touching patient surroundings

• Alcohol hand rub: 20-30 seconds (for visibly clean hands)
• Soap and water: 40-60 seconds (for visibly dirty/contaminated hands; mandatory after C. difficile)

Transmission-Based Precautions (additional to standard)

Prevention Bundles

• Insert only when necessary; use strict aseptic technique
• Maintain a closed drainage system
• Keep bag below bladder level
• Daily review of catheter necessity; remove as soon as possible
• Perineal hygiene

• Hand hygiene before insertion
• Maximal barrier precautions during insertion
• Chlorhexidine skin antisepsis
• Optimal catheter site selection (avoid femoral)
• Daily review of line necessity and prompt removal

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UNIT IX - Isolation Systems

Types of Isolation

• Source isolation (protective): Isolate infected patient to protect others
• Protective isolation (reverse isolation): Protect immunocompromised patient from environment

Isolation Rooms

• Positive pressure rooms - protect immunocompromised patients (e.g., bone marrow transplant)
• Negative pressure rooms - contain airborne pathogens (e.g., TB patients)

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UNIT X - Patient Safety

International Patient Safety Goals (IPSG)

1. Identify patients correctly - use at least 2 identifiers (name + DOB/hospital number)
2. Improve effective communication - SBAR (Situation, Background, Assessment, Recommendation); read-back of verbal orders
3. Improve safety of high-alert medications - double check concentrated electrolytes (KCl), insulin, anticoagulants
4. Ensure correct-site, correct-procedure, correct-patient surgery - surgical safety checklist/time-out
5. Reduce the risk of healthcare-associated infections - hand hygiene compliance
6. Reduce the risk of patient harm resulting from falls - fall risk assessment and prevention

Incident Reporting

• Near miss: Event that could have caused harm but didn't
• Adverse event: Event causing patient harm
• RCA (Root Cause Analysis): Systematic investigation of incident to find underlying cause
• CAPA (Corrective and Preventive Action): Actions taken to prevent recurrence

Occupational Safety - Needlestick Injury Management

1. Wash wound immediately with soap and water (do not squeeze)
2. Report to supervisor/infection control immediately
3. Document: date, time, instrument, source patient, depth of injury
4. Assess source patient for HIV, HBV, HCV
5. Post-exposure prophylaxis (PEP):
   • HIV: Start antiretroviral PEP within 72 hours (ideally <2 hours)
   • HBV: HBIg + Hepatitis B vaccine if unvaccinated
6. Follow-up testing at 6 weeks, 3 months, 6 months

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Quick Revision - Important Points

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Commonly Asked Exam Questions

• Gram staining procedure and significance
• Autoclave - principle and uses
• Standard precautions
• Chain of infection with examples
• Differences between sterilization and disinfection
• Koch's postulates
• Types of immunity with examples

• Describe the classification, structure, and pathogenesis of bacteria
• Explain Hospital Acquired Infections - types, risk factors, and nursing role in prevention
• Describe the immune response - innate and adaptive immunity
• Explain antibiotic resistance and the nurse's role in antibiotic stewardship
• Describe isolation precautions in nursing practice

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