Enterobacteriacae Flashcards
All Enterobacteriacae show what gram stain and morphology?
Gram-neg bacilli
What are the common biochemical traits of all Enterobacteriacae?
- Oxidase neg
- Catalase pos
- Reduce nitrate to nitrite
- Facultative anaerobe
- Ferment glucose
Most medically relevant family of GNB?
Enterobacteriacae
Enterobacteriacae associated diseases
- UTIs
- gastroenteritis
- septicemia
- food poisoning
- wound infections
- peritonitis
- pneumonia
- meningitis
What are the 4 antigens that contribute to Enterobacteriacae serological characteristics?
- O (Somatic) Ag for cell wall
- K (envelope) Ag for capsule
- H (flagellar) Ag
- Vi Ag
Capsular antigen of Salmonella typhi
Vi Ag
Heat stabilities of O, K, H, and Vi Ag
Heat stable = O
Heat labile = K, H, Vi
List enteric media
- MAC
- Eosin-methylene blue (EMB)
- Hektoen enteric (HE) agar
- Xylose-lysine-desoxycholate (XLD) agar
- Salmonella-Shigella (SS) agar
- Bismuth sulfite agar
- Brilliant green agar
- Selenite broth
MAC agar interpretation
- pink/red = lactose fermenters
- colorless = non-lactose fermenters
EMB agar interpretation
- colony with dark center = lactose fermenter
- colorless colony = non-lactose fermenter
HE agar interpretation
- yellow/orange = lactose and/or sucrose fermenters
- green = H2S neg, Shigella
- green with black center = H2S positive, Salmonella
XLD agar interpretation
- yellow = lactose and/or sucrose fermenter
- red with black center = Salmonella
- clear = Shigella
SS agar interpretation
- red = lactose fermenters
- colorless with black center = Salmonella
- colorless = Shigella
Bismuth sulfite agar interpretation
- black = Salmonella typhi
- yellow-orange = lactose fermenters
Brilliant green agar interpretation
- red/pink = Proteus and Salmonella
- no growth = Shigella and most lactose fermenters
Selenite broth interpretation
uncommon enhancement medium for stool cultures
- Salmonella enhanced
- normal GI flora are inhibited
Escherichia associated diseases
UTIs
appendicitis
peritonitis
gallbladder infections
endocarditis
meningitis in newborns
gasteroenteritis
food poisoning
Identifying traits of Escherichia
TSI slant
MAC
SBA sheep blood agar
EMB
Indole, methyl red, motility, ONPG
VP, citrate, and urease
- TSI slant: A/A and H2S neg
- MAC: pink/red colonies
- SBA: shiny, opaque, off-white, beta-hemolytic
- EMB: green metallic sheen with dark center
- Indole, methyl red, motility, ONPG positive
- VP, citrate, and urease negative
Enterohemorrhagic E.coli (EHEC) causes what?
Hemorrhagic colitis and HUS, leading to kidney failure in kids
How is EHEC acquired? Mechanism?
- Acquired by eating undercooked hamburger or other contaminated foods such as apple cider, basil, sprouts…etc
- Mechanism: Shiga toxin 1 and 2 virulence factors (E.coli O157:H7)
How to isolate and ID E.coli O157:H7?
- sorbitol MAC
- E.coli O157:H7 does not metabolize sorbitol -> colorless colonies
- other E.coli strains produce pink colonies
List all 4 strains of E.coli that cause human intestinal infections
- Enterohemorrhagic
- Enterotoxigenic
- Enteroinvasive
- Enteropathogenic
Enterotoxigenic E.coli
severe epidemic diarrhea due to contaminated water
Enteroinvasive E.coli
bloody diarrhea by invading intestinal epithelium
Enteropathogenic E.coli
watery diarrhea
Shigella causes what? Symptoms?
- Shigellosis
- Dysentery
- Abdominal pain, fever, diarrhea
Shigella most severe in what populations?
Children and elderly
Outbreaks common in daycare centers and nursing homes
How pathogenic is Shigella?
Highly pathogenic
Less than 50 bacteria can cause disease
Infection route of Shigella
Fecal-oral
food poisoning
Name the corresponding Shigella organism of serogroup A and describe
- S. dysenteriae
- Makes enterotoxin and neurotoxin that may result in paralysis
- Mannitol and ONPG neg
Name the corresponding Shigella organism of serogroup B and describe
- S. flexneri
- mild diarrhea
- mannitol pos and ONPG neg
- difficult to differ from S. boydii
Name the corresponding Shigella organism of serogroup C and describe
- S. boydii
- mild diarrhea
- mannitol pos and ONPG neg
- difficult to differ from S. flexneri