Swarming, beta-hemolytic bacteria - isolated from nostril. (Feb/20/2009 )

Hello everyone,

I'm a newbie and wanted to ask a question that has been bugging my professor and me for quite a while. For Microbiology class, us students were supposed to isolate Staph. aureus and Staph. epidermis from our own nostrils with a sterile swab, and streak-plate them. I performed the correct procedure according to protocol, incubated it for the same time as everyone else, and sterilized everything that needed to be sterilized. One exception: I had some slight blood on the swab as I had recently had a nosebleed.

However, my results turned out completely different from everyone else's.

We plated the nasal flora onto TSA and sheep blood agar plates. After 48h of incubation, I discovered that my cultures resembled nothing like Staph. aureus or Staph. epidermis. On the sheep blood agar, there were colonies growing in the areas I streaked. They weren't very distinct colonies and appeared to be capsules. What stumped everyone was the fact that the ENTIRE PLATE had turned brown, even in the areas I didn't streak. There was evidence of swarming with a rather undulate pattern away from the capsule bacteria, that just looked like a slightly rough, thin film, which isn't quite consistent with the Proteus genus of bacteria.

On the TSA plate, the agar had turned from yellow to yellow-brown. The capsules were present, but some had a slightly pink tinge, while others were a translucent yellow/white. I isolated part of a colony and performed another streak plate on TSA, which showed more indication of swarming and agar-darkening.

We were all very curious, so I performed a smear and a Gram stain. It was definitely Gram negative, and extremely small. Small enough that at 100x under oil immersion we couldn't tell if it was cocci, rod-shaped, or diplococci. I haven't performed a catalase test yet, and I'm currently trying to gather enough information to try plating it on different antibiotics.

This really isn't related to my schoolwork per se as I was allowed to borrow some of my lap partner's Staph epi for further labs, but my prof and I are just really, really curious. If anyone could lend us a hand in identifying this bacteria species, we'd greatly appreciate it.

are you sure you have a pure culture?

Yeah, I was wondering the same.

Why dont you do the test once more? This time without the blood or are you still having problems with your nose? if so, then no problem: even better for the test

maybe you should make a picture and post it here?

pito on Feb 21 2009, 12:54 PM said:

Well I noticed that there were two types of colonies...one that could be Strep due to its capsules (I'm feeling slightly sick now and am going to the health center later to ask the nurse to perform a Strep test because I'm very, very susceptible to Strep), and the other that was swarming from the areas I plated and into the rest of the agar. Now I know that Strep is non-motile so I'm just curious as to what the swarming bacteria is. I can try to take a photo next time I go into lab.

I'll definitely try to ask my professor if I could borrow another SBA plate and plate it without the blood this time. But I actually didn't have major problems with my nose...besides occasional stress nosebleeds with insignificant amounts of blood.

It's likely you have a Bacillus spp - propb source of both your swarming and appranet hemolysis. Not sure where you get "capsule" as characterizing strep - but it doesn't.

all depends on the Strep - S. mutans has a pretty good capsule, and some other ssp

if it's gram negative and tiny, it's very unlikely to be Bacillus

things to rule out might be Pseudomonas for your swarmer. for your capsular bug that sometimes looks a bit pink? try to look for Klebsiella (very gooey capsule, usually) or Serratia (which often turns pink at lower temperatures - try incubating at 28-30C and see if you get lots of pink)

those are the only ones I can think of. however, there are an awful lot of bugs that can colonize people...I'd purify the culture, then pick up a Bergey's and go through the algorithms.

good luck!

True - on some media ("gum drop " on mitis salvarius) but prob not on what was used here. In any case, you'd not id it based on colony morphology in mixed culture.

It's a mixed culture - not pure. So the Gram stain as well as colony morphology id not compelling. If only Gram neg's were present - it wouldn't be strep.

Failing the pure culture (and this appears to be intro micro), we can't say much.