Enteric Bacilli

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enterobacteriaceae

faculative GNR, non spore forming, can be motile or non motile; commonly called "fermenters"- comprise part of normal flora; "nonfermenters" primarily found in nature (opportunistic pathogens)

antigenic structure of enteric bacilli

1. flagellar H
2. somatic O
3. capsular K

flagellar H

heat labile; E. coli has about 50 different H antigens

somatic O

cell wall antigen, heat stable; E coli has 150+

capsular K

heat labile; E. coli has 90+

3 forms of salmonellosis

1. enteric fevers- typhoidal and nontyphoidal
2. septicemia/ extra intestinal infections
3. gastroenteritis (food poisoning)

pathogenesis of salmonella

1-3 week incubation followed by gradual increase in body temp, general achiness, continuous headache and often nonproductive cough; 2nd week- temp still high, diarrhea, abdominal pain
if no complications resolves in 3rd week

common infections from salmonella

gall bladder is almost routine, enlargement of the spleen, skin infection during bacteremic stage leads to local foci (red spots) on abdomen

reinfection of intestinal lymph tissue

causes: inflammation/ ulceration, releasing bacteria into intestinal lumen, bowel wall perforation in severe cases

description of gastroenteritis

lymphatic system contains spread of infection to intestine; symptoms being within 10hrs to 3 days following ingestion of contaminated food

symptoms of gastroenteritis

nausea, vomiting, diarrhea, belly ache, head ache, fever; lasts 2-7 days
- S. typhimurium and enteritidis are most common in US

diagnosis of salmonella

relys on isolation of the bacterium from appropriate clinical specimens and possible contaminated food source

treatment of salmonella

antibiotics- chloramphenicol, ampicillin, amoxicillin, and sulfamethoxazole; usually not given for gastroenteritis bc theu prolong fecal excretion and enhance development of drug-resistant strains

spread of typhoid/paratyphoid fevers

person to person; often asymptomatic carriers cause largest epidemics, about 3% of infected individuals become carriers

spread of nontyphoidal infections

via contaminated food/ drink; primary reservoir is farm animals and their products; only about 0.1% of patients become carriers

control of salmonella

maintenance of unpolluted water supply, inspection of product preparation in food industries, proper refrigeration of foods, detection of asymptomatic carrier and removal of those people from handling food

characteristics of shigella

4 species: S. dysenteriae, flexneri, boydii, and sonnei
all can cause shigellosis or bacillary dysentery; responsible for 10% of 5x10^6 deaths due to diarrheal diseases in children

pathogenesis of shigella

humans infected only, established via fecal-oral route; <100 bacterial cells needed to establish infection; can survive for 2hrs at pH 2.5

incubation/ symptoms of shigella

2-4 days, symptoms are fever, abdominal cramps and initial diarrhea; by day 2-3 epithelial necrosis in colon and low volume bloody diarrhea- classic signs of dysentery

effects of shiga toxin

enterotoxic, cytotoxic and neurotoxic effects, all of which reside in the same molecule. cleaves to ribosomes inhibiting protein synthesis and cell death, responsible for colonic vascular damage

treatment of shigellosis

generally a self limited disease; supportive therapy with fluid and electrolyte replacement usually efficient; antibiotic use shortens length of illness

epidemiology of shigellosis

world wide, spread via contaminated food and water; 60% cases in US occur in children, S. sonnei most common in US, S. flexneris most common in AIDS patients

control of shigellosis

safe water supply, effectie sewage treatment, education of food handlers in good hygienic practices

characteristics of E. coli

predominate faculative species in the colon; presence of water is an indicator of fecal contamination

pathogenicity of E coli

in normal habitat of intestine, usually doesnt cause disease and contributes to normal function and nutrition

infections of E coli

-UTIs- most common in women and infants; kidney infection can lead to chronic pyelonephritis
- sepsis & bacteremia- most frequent gram negative rod seen
- diarrhea- long known that certain strains cause diarrheal disease in infants and adults

4 mechanisms of E coli

enteroinvasive, enterotoxinogenic, enterohemorrhagic, enteropathogenic

enteroinvasive

(EIEC) strains penetrate epithelium of colon and cause inflammation; disease resembles dysentery

enterotoxinogenic

(ETEC)2 toxins, like V. cholerae toxin, inhibits absorption of Na and Cl, stimulates excretion of anions & water

enterohemorrhagic

(EHEC) shiga-like toxin

enteropathogenic

(EPEC) where bacteria atttach, microbillous border is lost, cytoskeleton is disrupted and eventual disruption of epithelial cell membrane occurs

treatment & control of E coli

most strains are sensitive to a variety of drugs, but sensitivity tests are a must
control- measures are usually not feasible- part of normal flora

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