Hello, I got some "red colonies" on Trypticase Soy Agar (TSA) and I was so curious about it. it was from the water sample of a shrimp pond. after I spread it, about 22 hours I got a little colony and I isolate it (like in the picture 1 and 2). then I got other two colonies from different sample but not as red as the first one (picture 3) but after 48 hours of incubation it become as red as the first one. I did some biochemical tests and gram staining on them such as catalase, oxidase, O/F and KOH. the result were catalse +, oxidase -, O/F + (fermentation) and gram -. as the result same as the literature on the internet I can guess the bacteria I isolated before was Serratia, but about the species, I was not sure it was marcescens.
so what do you think?
Nice pictures! In my view, you have enough information to be pretty confident that the isolate is Serratia - and probably S. marcescens. The glucose fermentation result is particularly useful to rule out some red/pink non-fermenting species. So unless the species ID is crucial, you could probably stop there. For definitive speciation, you would need to run some further biochemical tests or a commercial panel such as API 20E. For example, a test for ornithine decarboxylase would differentiate S. marcescens (+) from S. rubidaea (-), as the latter also produces the red prodigiosin pigment. Automated ID systems (if they are available to you) including MALDI-TOF MS should also give you a reliable species identification.
Thankyou for the answer I'll consider it if I get any red colonies again from the water samples. Thank you so much.
Please send your e.mail to me. I have some simple steps for preliminary identification of serratia
My e.mail [email protected]
About the notes of Prof. John D Perry Cultural characteristics are not enough for identification of bacterial genus or species because some bacteria gave the same characters, beside that some species of Serratia gave pale yellow
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