L3 - Enterobacteriaceae Flashcards
Enterobacteriaceae
- Water testing
- E. coli and other “coliforms” commonly found “only” in the bowel
- Coliforms or specifically E coli used as a public health indicator of fecal contamination of water (>4/dL)
- Coliforms are Gram-negative rods, lactose positive fermentation
True or False
Diarrheal disease constitutes the greatest single cause of morbidity & mortality in the world and kills over 10% of children in Latin America before age of 5
True
Secretory Diarrhea vs. Inflammatory Diarrhea
Secretory (watery) diarrhea
Example: cholera
- No WBC
- No RBC
- Watery, large volume
- Nausea, vomiting
- Afebrile (no fever)
Inflammatory diarrhea
Example: Shigella
- Presence of white blood cells
Neutrophils
Mononuclear
- Presence or absence of RBC
- Fever
Name the pathogens that fall under Secretory Diarrhea
- ETEC
- EPEC
- Cholera
- Salmonella typhi
- Salmonella non-typhi
Name the pathogens that fall under Inflammatory Diarrhea
- EHEC
- Shigella
- C. Jejuni
E. Coli
Physical and structural description
- Gram (-) bacilli, facultative anaerobe
classified into serogroups by O, H, and K antigen
- O is LPS
- H is flagella
- K is capsule
Example: O157:H7 (EHEC)
True or False
EHEC, EPEC, and ETEC are all found in the Large Bowel
False
EHEC is only found in the Large Bowel
EPEC and ETEC found in the Small Bowel
Name the E. Coli pathotypes
Enterotoxigenic (ETEC)
- heat-stable (ST) or labile (LT) toxin
stimulates hypersecretion of fluids in small intestine
Enteropathogenic (EPEC)
- adherence and destruction (A/E lesions) of cells
decreased fluid absorption
Enterohemorrhagic (EHEC)
- similar to EPEC but with shigatoxin
may progress to HUS
ETEC
- found in developing countries
- causes about 1/5th of all diarrheal illness in humans
- traveler’s diarrhea
- Fecal-oral transmission
- Secretory Diarrhea
- Rapid onset of watery diarrhea from mild to cholera-like, nausea, vomiting, no RBCs or WBCs
- Pathogenesis due to:
heat-stabile (ST) and heat-labile (LT) toxins
ST: increase in cGMP
LT: increase in cAMP
- Symptoms usually resolve without therapy
EPEC
- Infant diarrhea in underdeveloped countries
- EPEC adhere to epithelial cells lining small intestine via BFP
(A/E lesions)
- Secretory Diarrhea
- Malabsorption and watery diarrhea
usually without RBCs or WBCs
Type III contact-dependent
- TIR translocated into host cell by type III secretion system
- Intimin on EPEC bind TIR
- Microvilli rearranged
- Attaching and Effacing lesions formed
- Disruption of microvillus border alters intestinal absorption
EHEC
- found in developed nations (US and Europe)
- Cattle are reservoir
- Sporadic
usually outbreaks with common source
(spinach, lettuce, hamburgers)
- Forms A/E lesions like EPEC, usually not invasive
- Shiga-like toxin inhibits host cell protein synthesis resulting in cell death
- Possible dissemination and damage to kidney (HUS)
- O157:H7 = most common serotype
- Inflammatory Diarrhea
- Watery diarrhea that may progress to bloody, cramps, fever may be absent
How are the E. Coli pathotypes diagnosed and treated?
Diagnosis
- Culture on selective and differential medium
- MacConkey agar
If EHEC suspected sorbitol (-) = MacConkey (SMAC) agar
EHEC O157 are sorbitol (-)
most other E. coli are (+)
Treatment
Fluid and electrolyte replacement
Vibrio Cholerae
Pathogen
Gram (-) curved bacilli, polar flagellum, facultatively anaerobic
Origin
Fresh and Saltwater, infected humans may serve as a reservoir
- > 1 million bacteria needed to produce infection
- Convalescent carrier (asymptomatic or mild) possible
- El Tor (O1) survives longer in environment, may cause milder disease
- O139 Bengal associated with more recent epidemics
Transmission
- drinking water supply & fresh seafood
- fecal/oral
Disease
- severe watery diarrhea
Pathogenic Mechanism / Virulence Factor(s)
- hypersecretion of water and electrolytes through accumulation cAMP
- Expression of cholera toxin is co-regulated with expression of pilus
How is the Vibrio Cholera diagnosed and treated?
Diagnosis
- Grows on blood agar and MacConkey followed by serotyping
Vaccine
Prevention Oral vaccine testing by WHO, recommended for outbreak response
Treatment
- IV or oral hydration with electrolyte replacement with small amounts of glucose
- Antibiotics (severely ill, moderate to severe dehydration, hospitalized):
Adults: doxycycline
Pregnant women/children: erythromycin, azithromycin
Salmonella Typhi
- Obligate pathogen of humans
- Can cause enteric (typhoid) fever
- Antibiotics recommended
- May form carrier state <5% (gall bladder)
- Infectious dose ~1,000 (lower than non-typhi)
- Macrophages ingest & carry organisms via lymph and blood
Shigella
- Shigellosis (dysentery)
- >15,000 cases/year reported in US (2010)
- Most in children
- Fecal-oral transmission
- Infectious dose < 200 (low)
- Human disease only
- S sonnei most common in USA
- Invades colonic mucosa
- Inflammatory Diarrhea
- Cramping, bloody diarrhea
Virulence
- Invasin acts on GI cells to phagocytose
- Lyse phagocytic vacuole
- Directs host cell actin (contiguous spread)
- Shiga toxin inhibits protein synthesis
- Toxin similar to EHEC toxin
- Hemolytic uremic syndrome
