Exercise 11: Gram-Negative Study

Enterobacteriacea are a family of bacteria that share what same characteristics?

-gram-negative rods

-all ferment glucose

-all are nitrate positive

-all are oxidase negative

-many (but not all) are motile

All Enterobacteriaceae are pathogens, T or F?

false; many are harmless symbionts

What is the first one must run on a Enterobacteriaceae specimen? What plates are those ran on?

A lactose test and a sulfur reduction test; lactose is ran either on a E

If using a MAC plate, what color would a positive plate give? Negative?

-positive= pink color

-negative= no color change (no pink color)

If using a EMB plate, what color would a positive plate give? Negative?

-positive= growth with pink/lavender for weak lactose fermentation or growth with dark purple/green sheen for strong lactose fermentation

-negative= growth but no color change

For sulfur reduction, if you used a SS plate, what color what would a positive result yield? Negative

If the lactose test is positive, what color will it form? What is the next test one must run?

-MAC=pink; EMB=green sheen/dark purple (strong) or pink/lavender (weak)

-next test is IMViC

If the lactose test is negative, what color will it form? What is the next test one must run?

-will turn red (no yellow)

-next test is H2S Motility

Your specimen you are testing tested positive for lactose. You are now running a IMViC test. What does IMViC stand for?

-indole

-methyl red

-Voges-Proskauer

-Citrate

You ran the IMVic test and it tested positive for indole and methyl red, and negative for VP and Citrate. What do these tests look like color wise? What bacteria do you have?

-indole=cerise

-MR=red

-VP no color change

-citrate: no blue or growth

you have E. coli

You ran the IMViC test and it tested negative for indole and methyl red, and positive for VP and Citrate. What do these tests look like color wise? What bacteria do you have?

-indole=yellow

-methyl red=no color

-VP=red

-citrate= GROWTH; potential blue color

you have E. aerogenes

The specimen you are testing tested negative for lactose. What test do you need to do next?

H2S Motility

If you got a negative test for H2S/Motility, what will it look like?

No color change, no turbidity; organism stays within the stab line

If you got a positive test for H2S/Motility, what will it look like?

Black precipitate; turbidity away from stab line.

Your specimen tested negative for H2S/Motility. What test do you need to run next? If you don't need to run a test, what bacteria do you have?

no test is needed; bacteria you have is Shigella sonnei

Your specimen tested positive for H2S/Motility. What test do you need to run next? If you don't need to run a test, what bacteria do you have?

Need to run a urea broth test

For the urea broth test, what does a positive test yield? Negative?

-positive= lower pH; turns yellow

-negative= high pH; turns cerise

Your specimen test positive for urea. What bacteria do you have?

Proteus mirabilis

Your specimen tested negative for urea. What bacteria do you have?

Salmonella spp.

What test can be used to differentiate E. coli from E. aerogenes?

IMViC

What test can be used to differentiate Salmonella from Proteus mirabolis?

Urea broth and SIM (H2S and motility only)