lecture 1 continued Flashcards
Biochemical tests: IMViC test for e.coli , what does I, M, V and C?
I – Produces Indole
M – Methyl Red Positive
V – Voges-Proskauer Negative
C – Does NOT Utilize Citrate
what is principle of indole test ?
what is the reagent used in test?
and what does a pos result look like?
Some bacteria e.g e.coli split amino acid tryptophan into indole and pyruvic acid.
Indole reacts with aldehyde in the reagent -
pink/red colour which concentrates as a ring at the top
Bacterium to be tested is inoculated in
typtone/peptone broth (overnight at 37°C)
Add few drops of Kovac’s reagent
Pink ring = Indole positive
No colour change = Indole negative
what does Methyl Red – Voges-Proskauer (MR-VP) test for ?
glucose fermenting which all Enterobacteriaceae ferment.
what do enterobacteriaceae eg e.coli produce when they ferment glucose in mixed acid pathway?
pyruvic acid then some convert this to lactic, acetic or formic acid through a mixed acid pathway.
E.coli does this through this pathway
what do some enterobacteriaceae eg Klebsiella produce when they ferment glucose in butylene glycol pathway?
Klebsiella produces neutral product acetoin
in butylene glycol pathway.
what are the two pathways a bacteria can follow when fermenting glucose and producing acids?
- Mixed acid pathway
2.Butylene glycol pathway
what are the positive and neg result for Methyl Red?
pos=turns red e.g e.coli
neg= yellow/orange e.g Klebsiella
what are the positive and neg result for Voges-Proskauer?
pos= mahogany e.g Klebsiella
neg=no color change darker yellow e.g e.coli
Principle of Simmons Citrate Utilisation Test?
innoculate slant citrate agar. B.c citrate is the only available carbon source, if bacteria is able to grow, growth will increase ph of medium. Pos result= color change from green to blue e.g e. aerogenes
neg=green e.g e.coli
pH indicator bromothymol blue turns
blue at basic pH
what is TBX Agar? And what does it test for ?
Its tryptone bile glucuronic agar.
Tests for B-glucuronidase.
The chromogenic agent X- glucuronide used in this medium helps to detect glucuronidase activity. Escherichia coli cells absorb x-glucuronide and the intracellular glucuronidase splits the bond between the chromophore and the glucuronide.
Positive result on tbx agar?
pos= blue/green colonies e.g e.coli
neg = cream colonies
what temp and time do you incubate TBX agar?
18-24hrs at 44 degrees. and then you count colonies. This is the gold standard.
what are the four E.coli infection/ enteric infections strands?
- EPEC (enteropathogenic E.coli) - infant diarrhea
- ETEC (enterotoxigenic E.coli) – traveller’s diarrhea
- EIEC (enteroinvasive E.coli) – inflammatory dysentery
- EHEC/VTEC (enterohemorrhagic E.coli) – produce
verotoxins/shiga-like toxins (bloody severe diarrhea)
what strain of toxin does E.coli O157 produce ?
Shiga toxin type 2 also called verotoxin
how does E.coli O157 produce Shiga toxin type 2 and what disease does it cause ?
B subunits bind to the surface of intestinal cells, and its A subunits enter and turn off
protein synthesis by disrupting the large ribosomal subunit
Causes Haemolytic Uremic Syndrome (HUS) in very young/old
