GIT Infections - Bacteria Flashcards
Salmonella species are identified using both Poly O and Poly H antisera, why are species of Shigella only identified using Poly O antisera?
bc Shigella doesn’t have a flagella = no H Ag
What 3 key characteristics/tests would confirm that a species of Campylobacter had been isolated on CAMPY agar?
- Gram: GN helical/curved
- Oxidase pos
- unique tear drops colony growth along streak lines
- microaerophilic (low O2)
Which genera is chiefly responsible for causing dysentery? (3)
Shigella sp
Campylobacter sp.
Enteroinvasive E.coli
a)What is the primary reservoir of infection for Salmonella and Shigella? b) What relative infective dose of organisms is required to establish human GIT infection with each of these genera?
Salmonella: a) Animals reservoir b) >10^5 organisms
Shigella: a) human reservoir. b) 10-100 organisms
What organism(s) is responsible for causing enteric fever?
- S. “typhi”
- S. “Paratyphil A or B or C”
- both subspecies of Slamonella enterica subsp. enterica “_”
What colour reactions would you expect on XLD, DCA, TSI and urea for a Salmonella sp.?
XLD: Red colony black center
DCA: colourless w/ black center (bc H2S pos)
TSI: red slant, Acid butt w/ black
Urea: Neg
What colour reactions would you expect on XLD, DCA, TSI and urea for a Shigella sp.?
XLD: Red colony (transluscent)
DCA: colourless then pink (bc LLF)
TSI: Acid butt, red slant
Urea: Neg
What colour reactions would you expect on XLD, DCA, TSI and urea for a Proteus, Providencia or Morganella sp.?
XLD: Red/black colony= Proteus & Citrobacter (false +)
DCA: pale/black= Proteus & Citrobacter (false +)
TSI: yellow/red slant & black butt = Proteus
Red slant & yellow butt = Morganella, Providencia
Urea: Pos
What colour reactions would you expect on XLD, DCA, TSI and urea for a coliform (anyone of E.coli, K.pneumoniae, Enterobacter sp.)? HINT: all these look similar except maybe for mucoid colonies.
XLD: Yellow colonies (all 3)
DCA: varying shades of pink
TSI: Yellow slant and butt
Urea: Negative (all 3)
How does sorbitol MacConkey agar (SMAC) detect an EHEC strain?
Use sorbitol instead of lactose
O157:H7 E.coli (EHEC) is sorbitol neg after 24hrs = colourless
What are vero cells and what is a vero-cytotoxin?
Vero cells: are the African green monkey’s kidney cells
Vero-cytotoxin: aka Shiga toxin - cytotoxic (potents) to intestinal villi and colonic epithelial cells = excretion of water & electrolytes
Which serotype of Salmonella may be H2S negative in a TSI slope?
Salmonella Paratyphi A
*Slamonella enterica subsp. enterica Paratyphi A
Describe the three stages of enteric fever.
1st: Blood cultures pos (w/ Hx of fever)
2nd: Blood culture pos, Diarrhoea, faeces culture neg
3rd: Blood culture neg Diarrhoea, faeces culture pos
list the symptoms for gastroenteritis
vomiting, diarrhoea, nausea, abdo pain, fever
2 causes of diarrhoea
- Intoxication (food poisoning): ingest exotoxins = onset symptoms
- Colonisation of gut: ingest organisms = symptoms later
