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114 Cards in this Set
- Front
- Back
Define enteric bacteria
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All bacteria that inhabit the GI tract as commensals or as pathogens
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What is the typical bacterial flora in the large intestine
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Abundant: >90% anaerobes, 10% facultative Gram-negative rods (E. coli, staphylococci, enterococci and yeasts)
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What are the four general clinical syndromes of enteric intestinal infections
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Watery diarrhea; Dysentery; Hemorrhagic colitis; Enteric fever
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What are the characteristics of watery diarrhea
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Large volume; no leukocytes; nausea, vomiting, fever; Due to the action of bacterial enterotoxins
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What are the characteristics of dysentery
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Small volume stools containing blood and pus (inflammatory diarrhea). Fever, abdominal pain, cramps and tenesmus. Due to direct bacterial invasion or the production of cytotoxins
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What are the characteristics of hemorrhagic colitis
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Bloody diarrhea with or without inflammation. Linked to Hemolytic uremic syndrome
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What are the characteristics of enteric fever
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Systemic infection originating in the gastrointestinal tract. Penetration of the small bowel with spread to the biliary tract, liver, mesentery and reticuloendothelial system. Typhoid fever is a classic example
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What are the main diseases caused by enteric gram-negative bacilli
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Intestinal infections; Gastritis and peptic ulcer disease; Extraintestinal infections
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The vast majority of intestinal diseases caused by enteric bacteria are caused by which type of bacteria
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Frank pathogens
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What are the six main families of enteric bacteria covered in class
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Enterobacteriaceae; Campylobacteriaceae; Vibrionaceae; Helicobacter species; Pseudomonadaceae; Acinetobacter species
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What are the laboratory characteristics of Enterobacteriaceae
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Bacilli; Glucose fermenters; Oxidase negative; peritrichous flagella
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What are the laboratory characteristics of Campylobacteriaceae
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Tiny gull-shaped rods; microaerophilic; oxidase+
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What are the laboratory characteristics of Vibrionaceae
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Comma-shaped rods; Glucose fermenters; Oxidase+
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What are the laboratory characteristics of Helicobacter species
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Tiny, curved bacilli; Microaerophilic; urease+
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What are the laboratory characteristics of Pseudomonadaceae
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Bacilli; Nonfermenters; oxidase+
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What are the laboratory characteristics of Acinetobacter species
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Bacilli; nonfermenters; oxidase-
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What is one of the first steps towards identifying an enteric gram-negative rod
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Testing for the capacity of an isolate to ferment glucose
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What is the habitat of the enterobacteriaceae
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The lower intestinal tract of humans and other animals
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Which enterobacteriaceae do not ferment lactose
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Shigella sp, Salmonella sp, Yersinia sp.
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What three surface antigens are used to identify subsets of a species of enterobacteriaceae
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O somatic (terminal moiety of the LPS molecule); H (flagellar antigen, heat labile); Capsular (acid polysaccharides, poorly immunogenic)
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What are the general characteristics of the Shigella spp
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Gram negative, non motile, non-fermenter of lactose, H2S negative. Not considered normal human flora
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What is the group A Shigella serotype
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S. Dysenteria. Rare in the US, produces most severe disease (shiga toxin)
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What is the group B Shigella serotype
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Shigella flexneri. Most common in developing countries and among Native Americans
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What is the group C Shigella serotype
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S. boydii (rare)
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What is the group D Shigella serotype
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S. sonnei. Most common in the US and developed countries
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What are the main diseases of Shigella spp
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Shigellosis; bacillary or colonic dysentery
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Abdominal cramps, tenesmus and fever can occur in symptomatic infections of what microbe
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Shigella spp, which can cause Shigellosis or bacillary dysentery
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What are some common complications in Shigella diseases
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Convulsions in children; Hemolytic uremic syndrome; Reiter's syndrome
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What is Reiter's syndrome
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Post infection complication of Shigella infection consisting of aseptic polyarthritis, uveitis, and painful urination. Occurs in patients with the HLA-B27 histocompatibility antigen
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What are the specific steps of Shigella pathogenesis
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1. Transit through the stomach (infectious dose is very low)
2. Transient multiplication in the small intestine (enterotoxin production that produces watery diarrhea) 3. Colonization of the colon 4. Invasion of colonic epithelial cells (Pass through M cells and then invade epithelial cells from the basolateral surface) 5. Cause death of macrophages in the lamina propria by inducing apoptosis 6. Escape from the vacuole followed by cytoplasmic multiplication 7. Cell to cell spread |
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How does cell to cell spread occur in Shigella infections
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The bacterium induces an actin tail formation using host cell actin. It then releases itself from dead cells into the lamina propria, or directly passes between cells without exposure to the extracellular environment
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Intense, acute inflammation and destruction of colonic mucosa is indicative of what
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Invasion of colonic cells by shigellae. Death of mucosal cells creates ulcers and abscesses. Bloodstream dissemination is rare
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What do Shigellae carry that is responsible for numerous aspects of shigella pathogenesis, including invasion of host cells and cell to cell spread
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A large virulence plasmid
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What toxin does Shigella dysenteriae type 1 produce
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Shiga toxin
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What are some characteristics of Shiga toxin
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Cytotoxic and enterotoxic activities; inhibits protein synthesis in eukaryotic cells (28S of 60S); chromosomally encoded or transferred by bacteriophage
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How is Shigella transmitted
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Fecal/oral route, low dose. Shigellae are human specific.
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What is the epidemiology of Shigellae
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~18,000 cases of shigellosis are reported in the US annually; children 1-4 are most susceptible; crowding and poor sanitary conditions; enormous impact on military campaigns
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How is Shigella diagnosed in the acute stage
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Bacteria is present in large numbers in stool. Look for slow or nonfermenters of lactose
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How is Shigella treated
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Self limiting--do not impair intestinal motility. Trimethoprim/sulfamethoxazole for severly ill. Improve sanitary conditions. No vaccine available
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What are the general characteristics of Salmonella sp
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Facultative gram-negative rods, non-lactose fermenters, produce H2S, mostly motile
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What are the two Salmonella species
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S. enterica and S. bongori (bongori not very pathogenic)
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What antigens are Salmonella serotypes based on
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O,H,K
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What is the agent of typhoid fever
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Salmonella enterica Typhi
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How is typhoidal salmonella transmitted
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It primarily infects humans, so its transmission is via ingestion of food or water contaminated with infected human fecal material
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What are the clinical manifestations of enterocolitis
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Onset 6-48 hours after ingestion; nausea, vomiting, fever, ab pain, diarrhea; Self limiting
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What is the pathogenesis of enterocolitis
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Transit through stomach (many die) and colonization of small intestine; Multiplication and elaboration of an enterotoxin; Invasion of epithelium in terminal ileum and colon; recruitment of PMNs via IL-8; small numbers invade the submucosa
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What are the clinical manifestations of enteric fever (typhoid or paratyphoid fever)
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Incubation period 10-14 days; fever, anorexia; early constipation, late bloodly diarrhea; Rose spots on abdomen and chest
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How is laboratory diagnosis of typhoid fever made
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During the first week of Salmonella typhi infection, 80% of blood cultures are positive; 30-70% of stool cultures are positive in 2-4 weeks
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What is the pathogenesis of typhoid fever
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Bacteria adhere to and kill M cells, then penetrate intestinal lymph follicles; Multiply in macrophage vacuoles then disseminate through bloodstream to liver and spleen
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What are the complications of typhoid fever
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Secondary to toxemia (myocarditis, hepatic and bone marrow damage)
Secondary to GI lesions Secondary to persistence |
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What produces a N-acetyl galactosaminuronic acid surface polymer called the Vi capsule (antigen)
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Salmonella typhi. The antigen inhibits complement mediated killing
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What bacteria frequently cause sustained bacteremia with or without focal lesion
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Salmonella typhimurium and Salmonella cholerae-suis
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What are the clinical manifestations of bacteremia
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Fever, chills, weight loss; seen in patients with cancer
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What is the pathogenesis of bacteremia
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Can lead to focal lesions in lungs, bones, and meninges; subject to osteomyelitis, endocarditis. AIDS patients have higher risk.
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Chronic, systemic infections of bacteremia may be caused by what
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Schistosoma mansoni due to direct infection of the parasite by the salmonellae
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Who are the reservoirs for Salmonella typhi
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Humans are the sole reservoir. Can persist in the gall bladder. Infectious dose for Salmonella typhi is lower than for the enterocolitis-causing salmonellae
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Who are the principal reservoirs for nontyphoidal salmonella
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Animals
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What is the incidence of typhoid fever
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It was the most common type of salmonelloses in the US until the mid 1900s. Enterocolitis is now the most common form
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What is the incidence of enteric fever
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Salmonella typhi is a major cause of illness in developing countries; school aged children most at risk.
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What is the incidence of salmonella enterocolitis
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High incidence in the US. It is a disease of the industrialized world, due to large-scale food processing.
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What is the treatment for enterocolitis
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Fluid and electrolyte replacement; antibiotics generally not needed
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What is the treament for enteric fever and bacteremia
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Chloramphenicol or ampicillin. Can also use Trimethoprim/sulfamethoxazole or third generation Cephalosporins
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What vacines are available for Salmonella infections
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None for enterocolitis. Enteric fever include killed whole cell, live strain, and purified Vi antigen
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What are the general characteristics of Yersinia sp
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Facultative gram negative rods; non-lactose fermenters; optimal growth at 22-25 C. Not motile at 37C
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What are the medically important Yersinia species for humans
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Y. enterocolitica, Y pseudotuberculosis, Y pestis
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How are Yersinia enterocolitica and Y pseudotuberculosis transmitted
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They are primarily animal pathogens. Transmission occurs via ingestion of contaminated food
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What are some diseases caused by Yersinia sp
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Enterocolitis; Mesenteric lymphadenitis (entero and pseudo); Extraintestinal infections; Reiter's syndrome
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What is the pathogenesis of Y enterocolitica and pseudotuberculosis
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Similar to Salmonella typhimurium, enteriditis. Enters Peyers patches and replicates. Lymph node involvement, and can replicate in macrophages. Heat stabile toxin
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What are the virulence factors of Yersinia sp
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Chromosomaly-encoded invasins; Plasmid-encoded outer membrane proteins; heat stable enterotoxin (enterolitica)
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What is the epidemiology of Yersinia
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Highest rates in Scandinavia and Europe; Only certain serotypes are associated with disease; may need to alert lab to look for it.
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What treatment is needed for septicemia caused by Yersinia sp.
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Aminoglycosides, tetracyclines
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What are the general characteristics of E coli
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Facultatively gram negative, lactose fermenters. Cause intestinal and extraintestinal disease.
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What are the classes of diarrheagenic E coli
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Enterotoxic, Enteroinvasive, enteropathogenic, shiga toxin producing, enterohemorrhagic, enteroaggregative
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How did diarrheagenic E coli probably evolve
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From commensals via acquisition of virulence factors on bacteriophages, plasmids, and pathogenicity islands
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What disease is associated with enterotoxic E coli
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Acute secretory diarrhea. Copious, watery w/o blood or leukocytes. #1 cause of traveler's diarrhea
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What is the mechanism of pathogenesis for enterotoxigenic E coli
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Colonization Fimbriae provide attachement, Heat labile and Heat stable toxins are produced. No bacterial invasion occurs
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How do Heat labile and Heat stable work
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Activate adenylate cyclase and guanylate cyclase respectively
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What is the epidemiology of enterotoxigenic E coli
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Children in endemic areas, military personnel in endemic areas. Sanitation must be improved; milk with immunoglobulins can be produced. No vaccine
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What disease is caused by enteroinvasive E coli
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Bacillary dysentery identical to shigellosis. Stools are of scant volume and contain blood and neutrophils
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What is the mechanism of pathogenesis of enteroinvasive E coli
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They carry a large invasion plasmid of Shigella. Invade cells, multiply in cytoplasm, cell to cell spread
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What is the epidemiology of enteroinvasive E coli
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Common cause of diarrhea in children in developing countries. Human specific and transmitted from infected persons
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What disease is caused by enteropathogenic E coli
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Acute and chronic diarrhea in infants. Diarrhea is watery and without blood. May have moderate number of leukocytes
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What is the mechanism of pathogenesis in enteropathogenic E coli
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Attaching and effacing lesions on intestinal cells that efface the brush border.
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What are the virulence factors in enteropathogenic E coli
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Bundle forming pilus (mediates intestinal adherence); Intimin (adhesion necessary for formation of attaching and effacing (A/E) lesions)
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What is the epidemiology of enteropathogenic E coli
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Highest incidence in children <2 years old. Endemic in developing countries. Rarely infects adults. Breast feeding is protective
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What diseases are caused by enterohemorrhagic E coli and Shiga toxin producing E coli
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Mild diarrhea, Hemorrhagic colitis, and hemolytic uremic syndrome. Emerging infectious agent. Copious, bloody diarrhea occurs in hemorrhagic colitis with severe abdominal cramps. No fever, non invasive
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What are the mechanisms of pathogenesis of enterohemorrhagic E coli
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O157:H7 is the major US serotype. EHEC produces attaching and effacing lesions (A/E) identical to EPEC. Major site of pathology is the colon. Also produces a bacteriophage-encoded shiga toxin, likely responsible for HUS
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What is the pathogenesis of Shiga toxin producing E coli
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Produces a bacteriophage encoded shiga toxin, but lacks a pathogenicity island like EHEC, so it does not produce A/E lesions on intestinal cells
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What is the epidemiology of Enterohemorrhagic and Shiga toxin producing E coli
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> 110,000 illness in the US per year. Reside in commensals in cows and other animals. O157:H7 has very low infectious dose
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What is the treatment for enterohemorrhagic and shiga-toxin producing E coli
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Antibiotics may inducing toxin-encoding prophage, which can increase the risk and severity of HUS. Blood transfusion and renal dialysis is often performed for HUS
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What is enteroaggresive E coli associated with
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Acute and persistent diarrhea in children in developing countries. Has colonization fimbriae and heat stable enterotoxins
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What type of E coli does not ferment lactose
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Enteroinvasive E coli
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What strain of E coli does not ferment sorbitol
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O157:H7
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What are the general characteristics of Campylobacter jejuni
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Gram negative, comma-shaped rod, slow growing, motile, oxidase positive, microaerophilic
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What diseases are caused by Campylobacter jejuni
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Enteritis, colitis; Reiter's syndrome; Guillain Barre syndrome
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What are the characteristics of enteritis and colitis caused by Campylobacter jejuni
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Fever, ab pain, diarrhea. Bloody stools containing neutrophils, similar to Shigella. Acute colitis may be seen.
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What is the pathogenesis of Campylobacter jejuni
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Adherence to upper small intestine; invasion of tissue and inflammation. Colon is eventual target. Lipooligosaccharide (LOS) has structure similar to human gangliosides, leading to autoimmune Guillane Barre
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How is Campylobacter jejuni transmitted
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Undercooked chicken, other fowl
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What is the epidemiology of Campylobacter jejuni
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Most frequent cause of bacterial diarrhea in the US. High incidence worldwide, more frequent than Shigella or Salmonella
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When do symptoms of Guillain Barre syndrome appear
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3 Weeks after diarrhea from Campylobacter jejuni
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What is the treatment for Campylobacter jejuni
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Fluid and electrolyte replacement. Erythromycin in short duration (resistance is increasing)
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What are the general characteristics of Vibrionaceae
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Comma-shaped Gram negative rods, glucose fermenters, oxidase positive, polar flagella, abundant in marine and surface waters
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What serogroups cause chronic cholera
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Serogroups O1 (classical and El Tor) and O139 (Bengal) of Vibrio Cholerae
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What causes the acute diarrheal disease of cholera
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Enterotoxin. There is no bacterial invasion of host tissue. Can range from asymptomatic to cholera gravis
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What are the clinical manifestations of cholera
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Incubation 1-4 days, no fever but nausea, vomiting and profuse watery diarrhea with cramps; Rice water stools are characteristic.
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What is the pathogenesis of Cholera
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Survive acid stomach and multiply in bowel. Fimbriae called Toxin coregulated pili (Tcp). Produce cholera toxin
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What does the cholera bacteriophage use as a receptor
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The Tcp pili
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What does the B subunit of cholera toxin bind to
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GM1 ganglioside
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What is the major bacterial factor responsible for intestinal fluid secretion
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Cholera toxin
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How is cholera transmitted
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Ingestion of contaminated water or food. High dose is required (people actually volunteered to prove this)
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What is the epidemiology of cholera
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Seven pandemics since 1817. El Tor is the current pandemic (The name comes from the mountain where Moses received the commandments. Now you know).
Children are at greatest risk; risk to travelers; humans are only known host |
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How is cholera treated
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Fluid and electrolyte replacement. Oral hydration therapy works. Use tetracycline if you must
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How is cholera prevented
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Improved sanitation, Cooked food, vaccines
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What are the characteristics of Vibrio parahemolyticus
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Acute watery diarrhea. Short incubation period. Produces Kanagawa toxin. Associated with raw or undercooked seafood
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