TEST NAME for E.coli SUBSTRATE ENZYME DETECTED WHAT LEADS TO COLOR CHANGE? WHAT
ID: 262072 • Letter: T
Question
TEST NAME for E.coli
SUBSTRATE
ENZYME DETECTED
WHAT LEADS TO COLOR CHANGE?
WHAT DOES A POSITIVE TEST LOOK LIKE?
WHAT DOES A NEGATIVE TEST LOOK LIKE
HOW DO YOU INOCULATE THE MEDIA?
TIPS
Hydrogen Sulfide Production: (This data is obtained from the TSI test)
H2S is an end product when enzyme hydrolyzes amino acid cysteine
Indole Production:
Used to characterize enteric bacteria, (IMViC tests)
TEST NAME for E.coli
SUBSTRATE
ENZYME DETECTED
WHAT LEADS TO COLOR CHANGE?
WHAT DOES A POSITIVE TEST LOOK LIKE?
WHAT DOES A NEGATIVE TEST LOOK LIKE
HOW DO YOU INOCULATE THE MEDIA?
TIPS
Explanation / Answer
1) Indole test
**Substrate= tryptophan amino acid
**Result= indole
**Enzyme detected is TRYPTOPHANASE
**whats leads to colur change= when kovac's reagent is added to an overnight incubated broth of bacterial colony , it complexes with indole to produce cherry red colour.
**What does positive reaction looks like= red coloured ring near the surface of broth.
**What does negative reaction looks like= yellow coloured ring formed at surface.
2) TSI( TRIPLE SUGAR TEST)
**Substrate= three sugars( glucose, sucrose, lactose)
**Result= formation of H2S gas
**Enzyme detected= in TSI we detect three things= ability of organism to ferment sugars to produce acids, ability to produce gases, ability to produce H2S.
**What leads to colour change= bacteria produces H2S gas which combines with ferric ions to form ferrous sulfide produces blackening of medium.
**What does positive reaction looks like= blackening of medium
**What does negative reaction looks like= no blackening of medium( only fermentation i.e yellow colour of medium)
**How u incolate the medium= medium is inoculated with pure bacterial culture by straight wire pierced in stab culture and thn doing stroke culture on slant area and thn tubes are inoculated at 37degree celsius for 18-20 hours.
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