Bacteriology Lecture Notes Review

Introduction

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Content Overview

Outline of Bacteriology

• Gram Positive Cocci
• Anaerobic Gram-Positive Cocci
• Aerobic Gram-Positive Bacilli
• Anaerobic Gram-Positive Bacilli - Spore Forming
• Anaerobic Gram-Positive Bacilli - Non-Spore Forming
• Anaerobic Gram-Negative Bacilli
• Gram Negative Cocci
• Gram Negative Bacilli
• Non-Fermentative Gram-Negative Bacilli
• Curved Gram-Negative Bacilli
• Fastidious Gram-Negative Bacilli
• Haemophilus spp.
• Mycobacteria spp.
• Spirochetes
• Obligate Intracellular Bacteria
• HACEK Group
• Miscellaneous Bacteria

Gram Positive Cocci

Staphylococcus spp.

1. Staphylococcus aureus
      - Normal flora in anterior nares, nasopharynx, skin.
      - Causes:
        - Food poisoning
        - Skin and wound infections
        - Osteomyelitis
        - Staphylococcal scalded skin syndrome (SSSS)
        - Toxic shock syndrome (TSS)
      - Higher carriage rates in hospital personnel.
      - Methicillin Resistant Staphylococcus aureus (MRSA)
        - Associated with healthcare-associated infections.
        - Resistance due to beta-lactamase and altered penicillin-binding proteins.
        - Recommended treatment: Vancomycin.

2. Coagulase Negative Staphylococci (CoNS)
      - Generally part of skin flora and opportunistic pathogens in immunosuppressed patients.
      - Staphylococcus epidermidis
        - Infections associated with indwelling medical devices.
        - Causes UTIs and common in catheter-related infections.
      - Staphylococcus saprophyticus
        - UTIs in young, sexually active females and older men.

3. Micrococcus spp.
      - Includes Micrococcus luteus and Micrococcus roseus, normal flora of skin and environment.
      - Can cause opportunistic infections like brain abscess, meningitis, pneumonia and endocarditis.

Identification Methodology (Staphylococci)

• Gram Stain Results: Gram-positive cocci in clusters (S. aureus) vs. chains (Streptococci).
• Catalase Test: All Staphylococcus spp. positive (catalase + H2O₂ = H2O + O₂).
• S. aureus Characterization:
     - Golden color on sheep blood agar (SBA), coagulase positive, tolerant to 7.5% NaCl, yellow colonies on Mannitol Salt Agar (MSA).
• MRSA Detection: Optimal samples include anterior nasal & groin swabs. Utilize cefoxitin/oxacillin disk screening, PCR for mecA gene (gold standard).
• Micrococci Identification: Larger than staphylococci, arranged in tetrads, produce lemon-yellow colonies, sensitive to bacitracin.

Streptococci

Beta-Hemolytic Streptococci

1. Streptococcus pyogenes (Group A)
      - Causes pharyngitis, scarlet fever, skin infections, and rheumatic fever complications.
2. Streptococcus agalactiae (Group B)
      - Common in vaginal flora; causes neonatal infections (meningitis/sepsis).

Gamma-Hemolytic Streptococci

1. Enterococcus faecalis & faecium (Group D)
      - Causes UTI, endocarditis, and infections in the immunocompromised.
      - Resistant strains (VRE) treated with linezolid.
2. Streptococcus bovis
      - Associated with endocarditis and known to correlate with colon cancer.

Alpha-Hemolytic Streptococci

1. Streptococcus pneumoniae
      - Normal flora, causes pneumonia, meningitis, and otitis media.
      - Polysaccharide capsule vaccine recommended for vulnerable populations.
2. Viridans streptococci
      - Normal flora, associated with dental infections and endocarditis.

Identification Techniques for Streptococci

• Catalase Test: All Streptococci are catalase negative.
• S. pyogenes Characterization: Large beta-hemolysis on BA, sensitive to bacitracin.
• S. agalactiae Identification: Small zone of beta-hemolysis, positive CAMP test.
• Enterococci Features: May grow in 6.5% NaCl, positive bile esculin test.
• S. pneumoniae Identification: Lancet-shaped, bile solubility positive, optochin sensitivity.
• Viridans Streptococci Special Note: Sensitive to vancomycin.

Anaerobic Gram-Positive Cocci

Peptostreptococcus anaerobius

• Normal flora in mouth, skin, GIT, vagina; may cause infections under specific conditions (e.g., vaginosis).

Aerobic Gram-Positive Bacilli

Bacillus spp.

1. Bacillus anthracis
      - Causes anthrax; associated with animal products.
2. Bacillus cereus
      - Known for food poisoning and opportunistic infections.

Identification for Bacillus spp.

• Characterized by large, boxy, gram-positive rods, spore forming, catalase positive.
• Special staining: Malachite green for spore identification.

Corynebacterium diphtheriae

• Causes diphtheria. Diagnosed through culture on selective media, characteristic granules visible through special staining techniques.

Pathogenic Anaerobic Gram-Positive Bacilli

Clostridium spp.

1. Clostridium perfringens - causes gas gangrene, food poisoning.
2. Clostridium tetani - causes tetanus, characterized by terminal spores.
3. Clostridium botulinum - botulism due to neurotoxin.
4. Clostridium difficile - antibiotic-associated diarrhea.

Identification of Clostridium

• Clostridium spp. are motile, produce specific enzymes and toxins, identifiable by growth on specific agar media and toxin detection.

Anaerobic Gram-Negative Bacilli

Bacteroides fragilis

• Normal flora of the GIT; associated with abscesses and infections when displaced.

Gram Negative Cocci

Neisseria gonorrhoeae

• Causes gonorrhea and other infections; identified by specific culture techniques and Gram staining showing diplococci.

Moraxella catarrhalis

• Respiratory tract pathogen associated with various pulmonary infections.

Fastidious Gram-Negative Bacilli

Bordetella spp.

• Specifically B. pertussis causes whooping cough, needing specialized culture conditions.

Brucella spp.

• Causes undulant fever; transmitted via animal products.

Conclusion

• This comprehensive overview highlights the characteristics, identification methods, and pathogenic potential of various bacteria discussed throughout the presentation. These insights are crucial for diagnosis and treatment of bacterial infections.