Sometimes, I do come across a few things I find interesting going through the cultures. A huge part about clinical microbiology is about planting organisms on the plates. The whole point is streaking for isolation. In other words, finding out how many distinct colonies exist on the patient sample.
Whether you do it by hand, or through the use of automation, a streaked plate would usually look like this:
You start from your first quadrant and each streak into the new quadrant take less organisms. By the fourth quadrant, you would hope to be able to tell how many types of organisms are there.
I could dedicate an entire post on that subject, but moving on. Here is one of a patient's plates I came across this week. Don't worry, I have removed all the identification information. What's left is a snapshot via the BD Kiestra.
The source of this sample is bile.
As you can see, there are three distinct colonies on the MacConkey agar: two pink and one clear. Of the two pink (lactose fermenting) colonies, one of them is mucoid. I'm betting they are E. coli, a Klebsiella, and an Enterobacter species. Of course, I would have to conduct further testing to confirm those presumptions.
What you'll notice is that there is a clearing on the agar, and it seems to be on the first quadrant. No, nothing broke and the machine did according to its programming.
What you are seeing there is likely due to the fact that the patient is already on antibiotics. Often, this is a patient on empiric treatment until the lab could do some more digging for the clinicians. The clearing is due to the antibiotics. As we streak further out from the initial quadrant, there is less antibiotic. This allows bacteria to grow.
A clearing on the agar can happen when the source comes from a part of the body related to its filtration system. So yes, I have seen it before from kidneys and whatnot. It's not super common, but it does happen.
Things you could infer
A picture can tell you a bit of what is happening.
Patient does not have billiary obstruction. You wouldn't have a clearing otherwise.
The empiric treatment did inhibit bacteria growth as intended. Note that it doesn't kill all the organisms. It's the lab's job to find out what they are so doctors could prescribe more specific drugs.
Are those things relevant to me performing susceptibility tests on those organisms? Most likely not. But, it's somewhat entertaining to make connections and looking at the broader picture. In this case, it did jog a few memories.
The first time I saw that as a fresh technologist years ago, I thought it was an invalid culture. An older tech had to explain to me that is normal given the source (urine direct from kidney).
Anyways, it's another night at the lab.