Enterobacteriaceae Flashcards
Sites where members of the Enterobacteriaceae are considered “usual flora”
GI tract, uncommon normal flora of other areas
Sites where members of the Enterobacteriaceae are always considered pathogenic
Normally sterile areas
Characterisitics that are common among all members of Enterobacteriaceae
- GNR (straight)
- Facultative anaerobes
- Peritrichous flagella (if motile)
- Ferment glucose
- Nitrates reduced to nitrites
- Oxidase negative
- Grows well on MAC agar
What do Enterobacteriaceae generally look like on a SBA?
Large, smooth, gray colonies on SBA
Factors which contribute to pathogenicity of Enterobacteriaceae
- Endotoxins
- Exotoxins
- Invasiveness
- Adherence to epithelial cells
- Capsules
- Colonization
- Certain Ags
- Hemolysins/enzymes
When trying to isolate from areas w/ normal flora, you may need to…
Add several types of differential and selective media
- Stool → MAC, HEK, XLD for example
5 identification schemes of identifying Enterobacteriaceae
- Crosshatch/checkerboard
- Grouping systems
- Branching flow diagrams
- Numerical coding systems
- ?
Problem w/ crosshatch/checkerboard methods
Accurate but tedious
Problem w/ grouping system s(Edwards and Ewing)
Quicker but additional material may be needed
Problem w/ branching flow diagrams
Simple but dangerous
- Atypical organisms may be misidentified
Problem w/ numerical coding systems
Need to use your brain and not rely strictly on the number identification
Purpose of serologic typing
- Identification of isolate
- Epidemiologic “fingerprinting” (helps trace where it’s coming from)
Most frequently serotyped GNRs
- Salmonella
- Shigella
- Escherichia coli (selective isolates)
Serologic typing antigenic structure
- K (name and 3 facts)
Capsular Ag
- Polysaccharide
- Heat labile
- May block O Ag
Serologic typing antigenic structure
- H (name and two facts)
Flagellar Ag
- Protein
- Heat labile
Serologic typing antigenic structure
- O (name and two facts)
Somatic Ag
- Part of cell wall
- Heat stable
Serologic typing
- What media
- What antisera
- What to do if O group is blocked
Media: non-sugar containing and non-selective media (T. soy, SBA)
- Antisera: polyvalent
- If O group is blocked: boil organism and retype (b/c of capsule present)
Problems involved w/ the treatment of infections from Enterobacteriaceae
- High mortality rate for GN septicemia
- Antimicrobial resistance due to not taking all of antibiotics
- Potentially harmful effects of antimicrobials used for treatment
Habitat and most common infection involving E. coli
- Large bowel (#1)
- UTI (#1 most common cause)
- Gastroenteritis
Habitat and most common infection involving Shigella
- NOT normal flora (#1)/always pathogenic
- Penetrate epithelial cells of intestinal mucosa (blood, mucous, leukocytes)
Habitat and most common infection involving Salmonella
- NOT normal flora (#2)
- Gastroenteritis (animals)
- Septicemia (invasive)
Habitat and most common infection involving Citrobacter
- GI
- Variety of infections, primarily UTIs
Habitat and most common infection involving Serratia
- GI, also respiratory flora
- Formerly strictly saprophytic now
- Major nosocomial problem
Habitat and most common infection involving Enterobacter
- GI?
- Variety of infections, especially UTIs
Habitat and most common infection involving Proteus and Morganella
- GI?
- UTI…triple phosphate (struvite) crystals
- Renal stones
Habitat and most common infection involving Yersinia
Agent of the plague
- Bubonic (lymph)
- Pneumonic (lungs)
- Septicemic (blood)
Major source of infection for Enterohemorrhagic E. coli causing gastroenteritis
Hamburgers, fruits, vegetables, water (pools), ect.
Major source of infection for Salmonella causing gastroenteritis
Animals (chickens, turtles, iguanas, etc), food, water
Major source of infection for Yersinia pestis
Endemic in rodents and transmitted by insect vector, domestic cats to humans
Factors contributing to pathogenicity of EPEC and disease caused
Enterpathogenic E. coli
- Due to organism’s ability to adhere to cells in small intestine
- Infant diarrhea
Factors contributing to pathogenicity of ETEC and disease caused
Enterotoxigenic E. coli
- Due to toxins (heat labile toxin and heat stable toxin)
- Traveler’s diarrhea (Montezuma’s revenge) in developing countries
Factors contributing to pathogenicity of EIEC and disease caused
Enteroinvasive E. coli
- Due to ability to invade into mucosal cells of intestine not through blood
- Similar to Shigella (no specific disease caused)
Factors contributing to pathogenicity of STEC, EHEC, VTEC and disease caused
Shiga toxin, Enterohemmorrhagic, and Verotoxin E. coli
- Due to cytotoxins (verotoxins and “shiga-like” toxins)
- Leading cause of acute renal failure in children
Formulate an approach for isolating/identifying E. coli (O157: H7) in stool cultures
- Media?
- Biochemical recommendations?
- Typing recommendations?
???
- Use sorbitol MAC (will be sorbitol neg)
- Run a MUG test (will be m
Applications and advantages of shiga toxin testing on stool samples
- Some sorbitol positive STEC strains identified (would be missed by culture)
- Assay will detect serotypes other than O157
Compare and contrast the pathogenic mechanism involved in E. coli, Shigella, and Salmonellas gastroenteritis
???
Typhoid Fever
- Recommended type of specimen
- Characteristics of the disease
- Specific characteristics for identification of pathogen
- Test positive in blood cultures
- Man only host, invasive, high fever, carriers harbor in gallbladder
- Serotyping required for identification: it’s positive w/ Vi and group D antisera (may have to boil to get rxn w/ group D antisera)
Most common enteric agent of infection
- Urinary tract
E. coli
Most common enteric agent of infection
- Abdominal wound
??
Most common enteric agent of infection
- Newborn meningitis
??
Msot common enteric agent of infection
- Gastroenteritis
Salmonella
Most commen enteric agent of infection
- HUS
Enterohemorrhagic E. coli (STEC, EHEC, VTEC)
Most common enteric agent of infection
- Pneumonia
Klebsiella pneumoniae
Most common enteric agent of infection
- Typhoid fever
Salmonella typhi
Most common enteric agent of infection
- Plague
Yersinia pestis
Name 3 Enterobacteriaceae that are ALWAYS considered pathogens, regardless of specimen site
Shigella, Salmonella
Habitat and most common infection involving Klebsiella pneumoniae
- Bowel (#2)
- Pneumonia
- Nosocomial infections
How to differentiate K. pneumoniae vs. K. oxytoca via biochemicals
- K. pneumoniae is indole neg
- K. oxytoca is indole pos
How to differentiate P. mirabilis and P. vulgaris via biochemicals
- P, mirabilis is ornithine pos, indole neg
- P. vulgaris is ornithine neg, indole pos
How to differentiate E. coli and Shigella via biochemicals
- Shigella is always non-motile, lysine neg, lactose neg
- E. coli varies
- Serologic typing required before definitive identification can be made
Yersinia enterocolitica
- Disease
- How does someone contract it?
- Gastrointestinal (LN of small intestine) → children
- Contaminated water, food (esp. pork), unpasteurized milk, contact w/ animals
- Withstand refrigerator temperatures
Yersinia enterocolitica
- Stool culture
MAC, CIN, YSA at room temperature
