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35 Cards in this Set
- Front
- Back
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What are characteristics of Yersinia enterocolitica?
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Aerobic gram negative bacilli
Habitat/reservoir: domestic and farm animals (puppies) Transmission: fecal oral route |
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What does Yersinia enterocolitica do?
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Invades mucosa of terminal ileum
Causes painful enlargement of mesenteric lymph nodes (can be mistaken for appendicitis) Inflammatory and bloody diarrhea Transmitted by contaminated meat products (winter) Can grow at 4 degrees C |
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What is the virulence of Yersinia enterocolitica?
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Heat stable enterotoxin
Febrile illness with abdominal pain Often long-lasting: 2-3 weeks (can be acute or chronic) Infants: diarrheal illness common, occasional septicemia |
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How is Yersinia enterocolitica detected and treated?
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Isolation from stool and blood
Treatment indicated for infants with septicemia only |
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Describe the Aeromonas sp.
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6 species
Gram negative motile bacilli Water habitats: fresh, salt, chlorinated Very resistant: temperatures and chemicals Pathogenesis largely unknown Opportunistic pathogen: immune compromised |
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What are the characteristics of Vibrio sp.?
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V. cholerae, V. parahaemolyticus, V. vulnificus (uncommon)
Small, curved gram negative rods with single flagellum |
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What is the virulence and transmission of V. cholerae?
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Produces cholera toxin (exotoxin) - activates adenylate cyclase to increase cAMP
Voluminous watery diarrhea Transmitted by contaminated water or food (shellfish, crabs) Can survive long periods in aquatic environments - often major outbreaks |
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What does V. cholerae cause?
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Causes an acute illness due to enterotoxin production
Colonizes small bowel Severe form: rapid loss of liquid and electrolytes; hypovolemic shock; metabolic acidosis and death if untreated Acid sensitive bacteria - most ingested killed by stomach |
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How does V. cholerae cause GI problems?
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Attach to microvilli of epithelial cells in jejunum and ileum
Replicate and produce cholera enterotoxin, mucinase, and endotoxin (do not invade the mucosa) Toxins cause rapid loss of liquid from gut Watery diarrhea |
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Describe V. cholera's enterotoxin (cholera toxin).
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A-B type toxin
B binds GM1 monosialoganglioside, A migrates through epithelial cell membrane A1 has ADP-ribosyltranferase activity, transfer ADP-ribose from NAD to GTP-binding protein Increase adenylate cycalse activity and increase cAMP Water rushes into lumen and watery diarrhea results |
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What are the clinical manifestations of cholera?
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Abrupt, watery diarrhea (rice-water) - many liters of liquid lost in a few hours
Vomiting following diarrhea Cyanotic, sunken eyes and cheeks, scaphoid abdomen, poor skin turgor, voice high pitched or inaudible Vital signs include tachycardia, tachypnea and low or unobtainable BP Heart sounds distant or inaudible, bowel sounds hypoactive |
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How is cholera diagnosed?
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"Rice water" stools
Stool culture on TCBS (thiosulfate-citrate-bile-salt-sucrose) agar - selective for Vibrio V. cholerae colonies are yellow Other Vibrio sp. are green |
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How is cholera treated?
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Prompt replacement of fluids and electrolytes
Tetracycline may reduce severity and length of disease |
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How is cholera prevented?
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Killed whole-cell (WC) choler vaccine never been recommended by WHO bc low protective efficacy and high reactogenicity (25-50% effective)
Oral choler vaccines (OCV) safe and offer good protection (over 70%) for at least one year Neither used routinely in US |
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Describe V. parahaemolyticus.
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Hemolytic strains are most virulent
Enterotoxin production Moderate bowel inflammation, mild to moderately severe diarrhea Halophilic (salt loving) and grows in marine environments Commonly found in raw or undercooked shellfish |
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How is V. parahaemolyticus transmitted?
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Ingestion of inadequately cooked seafood or sushi
Colonize small intestine Virulence largely unknown but produces enterotoxin |
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What are the clinical manifestations of V. parahaemolyticus?
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Watery diarrhea, abdominal cramps, nausea, vomiting, fever, chills
Some cases have bloody diarrhea |
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How is V. parahaemolyticus diagnosed, treated and prevented?
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Culture the stool on TCBS medium
Treat with oral rehydration Prevention: eat cooked seafood |
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What are the 5 E. colis?
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1. ETEC: Enterotoxigenic
2. EPEC: Enteropathogenic 3. EaggEC: Enteroaggregative (or EAEC) 4. EIEC: Enteroinvasive 5. EHEC: Enterohemorrhagic |
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What are characteristics of E. coli?
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Gram negative motile bacilli
Lactose fermenting Habitat/reservoir: GI of humans and animals Transmission: fecal-oral route |
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Which E. coli cause non-invasive illness and which cause invasive disease?
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Non-invasive: ETEC, EPEC, EAggEC (do not see fecal WBCs)
Invasive: EIEC, EHEC (traits similar to Shigella) |
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Describe ETEC.
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Colonize small intestine
Common cause of traveler's diarrhea* Abrupt onset watery diarrhea, usually lasts less than 24 hrs after initiation of fluid replacement therapy |
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What are the ETEC toxins?
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1. LT/cholera-like/heat labile toxin - A-B toxin (1-A + 5-B)
B binds GM1 ganglioside on host cell, A endocytosed A in cytoplasm ADP-ribosylates GTP-binding protein, stimulates adenylate cyclase-cAMP system 2. ST/heat stable toxin - binds guanylate cyclase in apical membrane of intestinal epithelial cells Binding stimulates intracellular cGMP levels, stimualtes Cl ion secretion and/or inhibition of NaCl absorption |
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Describe EPEC.
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No known toxin
"Attaching-and-effacing" in small intestine Adhere to epithelial cells and disrupt microvilli Watery diarrhea with mild inflammation, infants <6 months |
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What does EPEC do to the epithelial cells?
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Intimately adhere to host cells, use type III secretory system and cause alterations in glycocalyx of gastric epithelial cells
Tir and Intimin Causes actin re-arrangement and pedestal formation Express rope-like bundles of filaments: bind bacterial cells to surface of epithelial cells |
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What are the three stages of EAggEC?
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1. Adhere to mucosa
2. Enhanced mucus production encases bacteria enabling biofilm formation 3. Elaboration of cytotoxin (kills host cells), damages intestinal cells May colonize small and large intestine, symptoms similar to most SI infection Common cause of more persistent diarrhea in adults and children |
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How are inflammatory E. coli infections diagnosed and treated?
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Isolation on MacConkey's agar
Specific testing for strain typing (test for toxins) Treated with IV or peroral replacement of the fluid and electrolytes Appropriate antibiotics may shorten duration of symptoms |
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What are the genetic traits seen EIEC and EHEC?
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EIEC has some genetic traits from Shigella sp. (same invasive capabilities)
EHEC acquired genes to express Shiga-toxins - cause cell death, edema, and hemorrhage in lamina propria |
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Describe EIEC.
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Very similar pathogenesis as for Shigella infections
Usually results in watery diarrhea - can also see scanty dysenteric stools Sporadic outbreaks in infants and children |
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Describe EHEC.
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Mostly infect large bowel - necrosis and infiltration of neutrophils
Kidney damage due to action of shiga toxin - swollen glomerular epithelial cells, fibrin deposition and infiltrates of inflammatory cells Sporadic with occasional outbreaks |
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What are the clinical manifestations of EHEC?
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Hemorrhagic colitis (HC): severe crampy abdominal pain, watery diarrhea followed by bloody diarrhea, little or no fever
Hemolytic uremic syndrome (HUS): triad of acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia HC usually precedes HUS |
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How are invasive E. coli infections diagnosed?
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Isolation and identification
EHEC O157:H7 - strain with most complications Carbohydrate sorbitol must be included in medium Inability to ferment sucrose ELISA detection of Shiga toxins 1 and 2 in stool |
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How are invasive E. coii treated?
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EHEC - avoid antibiotics (may kill bacteria and release more toxin, increases chance of HUS)
EIEC - usually self-limiting, treat severe cases with appropriate antibiotics |
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Describe Listeria monocytogenes.
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Gram positive rod with tumbling motility
Listeriosis Usually mild diarrhea but systemic symptoms prominent Pathogen can break into cytoplasm and divide Major risk in maternal infection during pregnancy Serious for immunocompromised |
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Which three pathogens are the most common cause of acute infectious diarrhea?
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Salmonella, Shigella, Campylobacter
Chronic illness - typhoid fever |
