Microbiology and Parasitology Review

Neisseria meningitidis

• Resistant to colistin, most saprophytic species of Neisseria susceptible

Bordetella pertussis

• Transmission: via respiratory droplets
• Virulence Factors:
  • Capsule
  • Beta lactamase
  • Filamentous hemagglutinin mediates attachment
• Toxins:
  • Pertussis Toxin: ADP ribosylation activates G proteins
  • Extracytoplasmic adenylate cyclase: inhibits phagocytosis
  • Tracheal cytotoxin: kills epithelial cells and paralyzes cilia
• Clinical syndromes: whooping cough, paroxysmal pattern of hacking coughs
• Diagnosis:
  • Nutritionally fastidious
  • Pleomorphic
  • Poorly gram-negative rods
• Treatment and Prevention:
  • Azithromycin
  • Levofloxacin
  • Doxycycline
  • Reducing cigarette and alcohol consumption
  • High temperatures and hyperchlorination in hospital water supply

Escherichia coli

• Metabolism:
  • Indole Positive
  • Lactose fermenter on EMB and MacConkey agar
  • Green metallic sheen on EMB
  • Triple Sugar Iron Agar shows acid with gas and no H2S production
• No H2S production

Shigella

• Biochemically inert enterobacteriaceae
• Transmission: infection
• Shigella is usually non-chalant since gastrectomy or use of antacids lowers infectious dose significantly
• Symptoms: N/V, abdominal pain, and nonbloody diarrhea
• Reactive arthritis (Reiter syndrome): triad of Uveitis, Urethritis, Arthritis
• Diagnosis: comma-shaped or S-shaped with single polar flagellum
• Treatment and Prevention: symptomatic treatment, Erythromycin for severe cases

Campylobacter jejuni

• Necrotizing Pneumonia
• Usually nosocomial with thick bloody sputum
• UTI
• Sepsis

Haemophilus influenzae

• Facultative with large polysaccharide capsule
• Currant jelly sputum
• Treatment and Prevention: culture-guided treatment, Cephalosporins +/- Aminoglycosides

Proteus mirabilis

• Metabolism:
  • Urease positive
  • Indole negative
  • Non-lactose fermenter
• Virulence Factors:
  • Motile
  • Fimbriae for adherence
  • LPS
  • Urease production
• Clinical syndromes:
  • Complicated UTI associated with nephrolithiasis
  • Sepsis

Helicobacter pylori

• Metabolism:
  • Microaerophilic
  • Oxidase positive
  • Catalase positive
  • Urease positive
  • Triple positive
• Transmission: ingestion, habitat: human stomach
• Virulence Factors:
  • Urease produces ammonia makes the environment alkaline

Aminoglycoside Ineffective Bacteria

• Aminoglycoside antibiotics are ineffective against anaerobes because they require oxygen to enter the bacterial cell
• Examples of anaerobes include Clostridium, Bacteroides, Fusobacterium, and Actinomyces
• Other bacteria that are not affected by aminoglycoside antibiotics include Helicobacter pylori, Legionella, Bartonella henselae, and certain fungi

Staining Techniques

• Silver Stain is used to diagnose Helicobacter pylori, Legionella, and Bartonella henselae infections
• Periodic Acid Schiff Stain is used to diagnose Whipple disease (Tropheryma whipplei)

Anaerobes and Facultative Anaerobes

• Anaerobes (e.g. Clostridium, Bacteroides, Fusobacterium, Actinomyces) cannot use oxygen and require fermentation
• Facultative anaerobes (e.g. Helicobacter pylori, Legionella) can use oxygen if present, but can also use fermentation in its absence

Bordetella Pertussis

• Transmission: whooping cough is highly contagious during the catarrhal phase (1-2 weeks)
• Incubation period: 7-10 days
• Diagnosis: small rods, culture in Bordet-gengou agar, ELISA, PCR detection of bacterial DNA
• Treatment and Prevention: Erythromycin, DPT vaccine, treat household contacts

Legionella Pneumophila

• Metabolism: growth depends on L-cysteine and Iron in chocolate yeast extract agar
• Transmission: ubiquitous in man and natural water environments, airconditioning systems
• No person-to-person transmission
• Virulence Factors: facultative intracellular organism, cell-mediated immunity is important
• Toxins: endotoxin, cytotoxins
• Clinical syndromes: Pontiac fever, atypical pneumonia, Legionnaires' disease

Escherichia Coli (E. Coli)

• Virulence Factors: fimbriae, pili, capsule (K antigen), flagella (H antigen), siderophore
• Toxins: endotoxin, entero toxins
• Clinical syndromes: BEL (neonatal meningitis), UTI, nosocomial sepsis, nosocomial pneumonia, diarrhea
• Subtypes: ETEC, EIEC, EPEC, EHEC (O157:H7)

Shigella spp.

• Virulence Factors: motile shooting star motility, fimbriae
• Toxins: choleragen
• Clinical syndromes: severe diarrhea with blood and pus in the stool, dysentery