Enterobacteriaceae Part 1 & 2 Flashcards
What are some general characteristics of Enterobacteriaceae ?
- commonly found in GI and water and dirt samples (all over our environment)
- gram (-) rods
- facultative anaerobes (prefer O2 resp but will do fermentation too)
- some are motile
- are fermenters (all can ferment glucose)
- oxidase (-)
- non spore forming
What are the uses of a MacConkey Agar ?
to differentiate lactose fermenting from nonlactose fermenting gram (-) bacteria (no growth of gram + cocci)
- isolates gram (-) enteric bacteria
- pink= lactose fermenting (mixed acids are produced which lowers pH which turns it pink)
- colorless= nonlactose fermenting
What is the use of the Indole test ?
determine if the bacteria produce the enzyme tryptophanase
- Kovac’s reagent will detect indole
- says tryptophan is present and the bacteria could use it to produce indole, pyruvic acid, and ammonia
- +: red ring at broth surface
- (-): no formation of red ring
What is the purpose of a methyl red (MR) test ?
determines whether the microbe performs mixed acids fermentation when supplied glucose
- creates acidic products which lowers pH
- breaking down or fermenting the glucose
- +: red color (low pH, acidic)
- (-): no methyl red color
What is the purpose of Voges-Proskauer (VP) ?
indicates a form of glucose fermentation called butanediol fermentation
- makes neutral products and acetyl methyl carbinol
- done in same broth as methyl red test
What is IMViC ?
Indole test, Methyl red test, Voges-Proskauer test, and citrate utilization test
- 4 tests that are usually run together to identify/differentiate the members of the Enterobacteriaceae family
What is the purpose of a Kligler’s Iron Agar (KIA) ?
- detects the fermentation of glucose and lactose
- detects the production of hydrogen sulfide and carbon dioxide
- the butt is for reading glucose
- the slant is for reading lactose
- has to be read within a certain amount of time since the colors can reverse
What is the advantage of doing a Phenol Red Broths test over KIA ?
the color does not reverse after a period of time unlike the KIA test
What is the most common enterobacterial infection in the U.S ?
E. Coli infections
What is gastroenteritis ?
inflammation of the lining of the stomach and intestine
- mild to severe diarrhea, low grade fever, varying degrees of nausea and vomiting
What is toxigenic diarrhea ?
bacteria release enterotoxins onto the surface of the small intestine
- bacteria doesn’t invade the tissue but toxin does damage to tissue
- large volume of stool with little blood
- seen with cholera, some E.coli and shigella
What is invasive diarrhea ?
organism invade the wall of the intestines
- disrupts the structure leading to gross injury
- smaller fecal volume, rectum pain, blood in stool, and ulceration of inner mucosal lining
-seen with salmonella, some E.Coli, and Campylobacter
What is the greatest single cause of mortality among babies ?
infantile diarrhea
- in some areas of the world it’s 15-20% in kids < 5 yrs die
- usually results from feeding baby contaminated food and water
- common in crowded tropical regions
- encourage moms in 3rd world countries to breastfeed
What are some conditions for higher rates of infantile diarrhea ?
crowded tropical regions with poor sanitary facilities, contaminated water supplies, and adults carry pathogenic strains to which they have immunity
What are some characteristics of Enterotoxigenic E.Coli (ETEC) ?
produces an enterotoxin that causes a secretory diarrhea
- Traveler’s diarrhea /Montezuma’s revenge/Delhi belly
- travelers encounter the bacteria that the local population have developed immunity
- symptoms last 5 to 15 days
- bacteria must attack to surface of the intestinal epithelial cells for toxin production to occur
What are some characteristics of Enteropathogenic E.Coli (EPEC) ?
inflammatory reaction to breakdown of intestinal epithelium
- pathogenesis is unclear
- causes diarrheal symptoms mostly in children
Which E. Coli is ETEC ?
Enterotoxigenic E.Coli
- toxigenic
Which E.Coli is EPEC ?
Enteropathogenic E.Coli
- invasive
Which E.Coli is EIEC ?
Enteroinvasive E.Coli
- invasive
What are some characteristics of Enteroinvasive E.Coli (EIEC) ?
bacteria penetrate the intestinal epithelial cells causing a inflammatory diarrhea
- feces contain blood, mucous, and WBC
Which E.Coli is EHEC/VTEC ?
Enterohemorrhagic E.Coli
- toxigenic
What are some characteristics of Enterohemorrhagic E.Coli (EHEC) ?
associated with hemorrhagic colitis and hemolytic uremic syndrome
- produces bloody diarrhea due to toxin damage of epithelial cells
What is hemorrhagic colitis ?
present with abdominal cramps and watery diarrhea followed by blood diarrhea
- no significant fever or WBC in stool
What is hemolytic uremic syndrome ?
leading cause of acute renal failure in children
- only type of E.Coli that is sorbitol (-)
- distinguished by using MAC with sorbitol instead of lactose
