Bacterial diseases caused by Gram-negative rods

Virulence factors

Endotoxin
Capsule
Type III secretion systems
Iron sequestration
Serum resistance

Major pathogens

E. coli
- Enterobacteria; most are lactose-fermenting
- Adhesins (CFA, AAF, Bfp, P-pili, intimin, Ipa protein, Dr fimbriae)
- Exotoxins (Shiga toxin, heat-stable enterotoxin, heat-labile enterotoxin)
- Gastroenteritis (exogenous): watery diarrhea in most; may be bloody (EI, EH); nausea, cramps, vomiting may be present
  - ETEC: enterotoxins (STa, LT-I) activate AC and GC = hypersecretion; f/o
  - EPEC: damage to microvilli (A/E lesions) = malabsorption; person-person
  - EIEC: invasins help EC enter colonic epithelial cells
  - STEC/EHEC: Shiga toxins damage GI epithelial cells, kidney cells; food-borne
  - EAEC: EC aggregate and damage microvilli
  - DAEC: Watery diarrhea in infants to 5 yrs old; microvilli elongate
- Urinary tract infections (endogenous)
  - Adhesins and hemolysins = inflammation
- Sepsis: most common Gram-negative rod; often nosocomial
- Neonatal Meningitis: capsule
Salmonella
- Transmission via contaminated food; many animals can be reservoir (Zoonotic)
- Salmonellosis (enteritis)
  - Invasion of M cells in ileum = cell death, inflammation, stimulation of fluid secretion
  - Onset within 48 hrs, duration < 1 week
  - Infection may spread into bloodstream (bacteremia)
  - Zoonotic: animal carriers; high ID50
- Typhoid fever: S. typhi
  - S. typhi pass through instead of killing M cells.
  - Enter macrophages, spread to liver, spleen, bone marrow.
  - Fever, headache, myalgia, malaise, reinfection of GI tract via gallbladder
  - reservoir = human carriers; low ID50
  - 200,000 deaths worldwide/yr
Shigella
- Transmission is fecal-oral; primarily in children < 15 yrs old (ID50 ~ 200)
- Shigellosis (gastroenteritis, dysentery): bloody diarrhea
  - Invasion of M cells in colon; damage to colonic epithelium after passage through epithelium
  - Shiga toxin inhibits protein synthesis; Shigella also induces apoptosis
  - Inflammation, leukotaxis contribute to damage
  - Cramps, diarrhea, fever, hemorrhage within 3 days
Yersinia
- Plague: Y. pestis
  - Rats, rabbits, cats, squirrels can be reservoirs (Zoonotic)
    - sylvatic: wild animals; urban; rats
  - Transmission via vector (flea)
  - Virulence factors to avoid phagocytosis, inactivate complement, break down fibrin clots = rapid spread
    - YopH, E, J, P damage/kill phagocytes
  - Bubonic plague: systemic bacteremia, 75% mortality
  - Pneumonic plague: aerosol transmission, shorter time course
- Gastroenteritis: Y. enterocolitica
  - Contaminated food or water
  - 1 - 2 week course of diarrhea, cramps, fever + pain
Klebsiella
- Community-acquired pneumonia
  - K. pneumoniae and K. oxytoca
  - Capsule; bacteria can cause necrosis and bloody sputum
- Hospital-acquired pneumonia (nosocomial)
  - Antibiotic resistance
- Granuloma inguinale
  - K. granulomatis (formerly Calymmatobacterium)
  - STD: formation of nodules (granulomas) which break down and form painless genital lesions
Pseudomonas aeruginosa
- Gram-negative obligate aerobes, oxidase-positive
- Ubiquitous in nature and hospital settings
- Opportunistic pathogens with numerous virulence factors such as elastase, protease & phospholipase
  - pyocyanin (green-blue pigment): release of IL-8, inflammation, tissue damage
  - capsule: cystic fibrosis
  - Exotoxin A (inh. protein synthesis); Exoenzymes S & T
- Antibiotic resistance
- Diseases
  - Pneumonia (can be necrotizing)
  - Skin infections (burn wounds, ecthyma gangrenosum, folliculitis)
  - UTI (catheterized patients)
  - Swimmer's ear (otitis externa)
Bordetella pertussis
- Gram-negative aerobic coccobacilli; fastidious
- Whooping cough
  - Exclusively human reservoir
  - Many exotoxins (pertussis toxin, dermonecrotic toxin, tracheal cytotoxin) and adhesins
  - Cold-like symptoms (1 - 2 weeks), then whooping cough paroxysms (2 - 4 weeks) with vomiting and exhaustion
  - Systemic toxemia possible
  - DPT vaccine
Francisella tularensis
- Tularemia (rabbit fever)
  - Zoonotic: Reservoir is wild mammals, birds, fish, ticks
  - Gram-negative coccobacilli, aerobic, fastidious
  - Transmission: direct contact, vector, or aerosol
  - Pathogenesis: intracellular pathogen in Macrophages
  - Difficult to culture and identify
Brucella
- Brucellosis (undulant fever)
  - Zoonotic: Animal reservoir; transmission by direct contact or contaminated food
  - Intracellular pathogens (macrophages) - cause granulomas in organs
  - Initial symptoms are non-specific (malaise, chills, sweats, fatigue etc)
Haemophilus
- Fastidious Gram-negative rods
- Capsule + virulence factors = damage to respiratory epithelium
- Translocation across epithelium can lead to bacteremia
- Childhood vaccine has drastically cut pediatric infections
  - Otitis and sinusitis: H. influenzae b (Hib)
  - Meningitis (pediatric): Hib
  - Epiglottitis: life-threatening; Hib
  - Chancroid: STD, mainly in males; H. ducreyi
  - Otitis, sinusitis, respiratory tract infection: non-encapsulated H. influenzae
  - Brazilian purpuric fever: Starts with conjunctivitis; if untreated, often fatal (shock)
Legionella pneumophila
- Pleomorphic Gram-negative rods; fastidious
- Transmission is via aerosol from contaminated water sources (e.g. air conditioning)
- L. pneumophila invade and live in macrophages, which they eventually kill
- Legionnaire's disease
  - Fever, chills, cough, headache, multiorgan disease, pneumonia w/ 15 - 20% mortality
Bartonella
- Most are Zoonotic: often transmitted via vectors
- Cat scratch disease : B. henselea
  - Transmission by direct contact (cats) & fleas (vector)
  - mild, self-resolving symptoms
- Trench fever: B. quintana
  - severe headaches, long bone pain, fever (may recur every 5 days);
  - human reservoir, transmitted by body louse (vector)
  - Bacillary angiomatosis: severe infections in immunocompromised
- Bartonellosis (Oroya fever): B. bacilliformis
  - severe anemia + chronic cutaneous nodules (verruga)
  - Bartonella infects RBCs
  - Transmission via sandfly vector (S. America)
Burkholderia
- nosocomial infections (B. cepacia) - pneumonia, UTI, sepsis
- Melioidosis (B. pseudomallei) - bioterror threat
Acinetobacter baumannii
- Opportunistic infections (nosocomial)
  - Multiple drug resistance!
- Wound infections (esp. war wounds) - Iraq
Aeromonas hydrophila
- Gastroenteritis
- Wound infections
Streptobacillus moniliformis
- Rat-bite fever (Zoonotic)
- Haverhill fever (contaminated food, water, milk, turkey)
Bacteroides, Prevotella, Porphyromonas, Fusobacterium
- Obligate anaerobes; resident microbes
- Respiratory tract, brain abscesses, abdominal infections
- Periodontal disease

Major diseases

Intestinal tract infections
- Gastroenteritis
- Salmonellosis (enteritis)
- Shigellosis (dysentery)
Zoonotic infections
- Bartonellosis
- Brucellosis
- Tularemia
- Rat-bite fever
Lung/respiratory infections
- Legionnaire's disease
- Pneumonia
- Whooping cough
Systemic infections
- Plague
- Typhoid fever
Urinary tract infections
- E. coli
Wound infections
- Pseudomonas
- Acinetobacter
- Aeromonas
Sexually Transmitted (STD)
- Chancroid
- Granuloma inguinale
Vector borne
- Bartonellosis
- Cat scratch disease
- Trench fever
- Tularemia
- Plague

Summary

Cause:
Microscopy:
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Treatment: