lec 13 - indole, citrate, TSI, SIM

what does the indole production reaction test for?

tryptophanase (enzyme) presence

what is tryptophan hydrolyzed by

tryptophase

what reaction does tryptophanase hydrolyze?

tryptophan → indole + pyruvic acid + ammonia

what reagent is indole detected with?

kovac’s

what do positive and negative results after kovac’s during an indole test?

positive has a dark red color in a ring and negative has no red ring (colorless)

what is the citrate agar test testing for?

used to distinguish spp. of enterobacteriaceae

what does visualizing citrate produce?

an alkaline carbonate which increases pH

what ingredients are in simmon’s citrate agar?

citrate, ammonium salts, bromthymol blue

when pH (positive reaction) is increased in a citrate agar test, what is the color change?

green to blue

what is a negative outcome in a citrate test

agar remains green; no change in pH

what is a SIM test?

distinguishes gram negative bacteria found in the gut

what does SIM stand for?

sulfide-indole-motility

what is the positive and negative results of a S in SIM?

positive is sulfide production and black precipitate and negative is no sulfide production no color change (remains yellow)

what is the positive and negative of the I in the SIM test?

positive is a red ring meaning a production of indole and negative is no red ring meaning no indole production

what is the positive and negative of the M in SIM?

positive is a turbid tube and negative is the turbidity stays at the stab line

what three sugars are in TSI?

dextrose, lactose, and sucrose

what does TSI stand for?

triple sugar iron

what can you see from a TSI tube? what does it show?

cracks in the media means gas production and black precipitate (at the bottom) for sulfide production

what does a yellow slant and yellow butt mean in TSI?

ferments high conc. of a d-glucose and (sucrose and/or lactose); slant stays yellow even after peptide degradation (~18-24 hours incubation)

what does a red slant and yellow butt mean in TSI?

ferments d-glucose only; the slant stays red and the butt stays yellow even after peptide degradation to alkaline products (~18-24 hours)

what does a red slant and red butt mean in TSI?

no sugar fermentation; it is aerobically degrading peptides to produce alkaline products

how is an anaerobic or aerobic environment created in the TSI media?

stabbing into and streaking onto slant