Ryan asked:


What is the basis of different colored colonies of an EMB agar and a MacConkey agar?

For example, C.Freundii tested positive with a bright pink color in the Mac agar and positive with dark colonies in the EMB agar but P.vulgaris tested negative with no color in the Mac agar and positive with dark colonies in the EMB agar.

pochacco630 asked:

On the Maconkey plate, i saw red colonies and clear colonies and on the Hektoen plate i saw yellowish-orange colonies and colonies with black centers (H2S) production. But when i tried to isolate them on the Hek plate again, I cannot see growth from the black dotted colonies at all, while there was the same growth of orange-red colonies from the other organism. Is it possible that the black dotted colonies can disappear? i’m just confused; i’ve done the gram stains and both are gram neg. rods while the reddish-orange colonies resembles dipplo-cocci looking rods and the clear black dotted colonies had a small thin gram neg rod with majority of short rods. Oxidase test was done on both, and both are oxidase neg. Any helps to what i should focus on as to their identities? I know that one is a glucose fermenting organism while the other, i’m just not sure since i wasnt able to do any other chemical tests on it yet. i just want to have an idea of where i should be headed.
ok, i just had results for some other tests that were available: first organism with the purple-pink colonies in the MAC plate had A/A on the DSIA, + citrate, -urease, nonmotile,+indole -H2S. The 2nd organism with clearish brown colonies on the MAC plate is K/A for DSIA, H2S+, motile, citrate -, urease -, indole-, So any leads? I think the 1st organism is Klebsiella while the other is Salmonella.