How can I confirm contamination in Bacillus subtilis culture without sequencing?

[PaisleyVH]

I’ve been culturing what I thought was a pure sample of *Bacillus subtilis* for a simple sporulation experiment, but my last gram stain showed what looks like a second, rod-shaped bacterium present. I’m unsure how to proceed with verifying the contamination without access to a sequencing core right now.

[James.R]

That happens. Gram stains can mislead, and endospore forming rods can look like a second organism. A contaminant from air, media, or a previous culture is possible. The main thing is to pause and document, not push forward until you have confirmation.

[PenelopeW]

Without sequencing, you won’t be sure, but you can look for patterns you already know—colony shape, color, how they grew on your media—but none of that is definitive. Best path is to pause, quarantine the sample, and loop in biosafety/compliance or the core facility for guidance when available.

[MiaC]

Could this be a staining artifact or misread rather than a real contaminant?

[AlexanderB]

I’ve had a moment like this and kept going, then wished I hadn’t. It was messy, but it forced me to rethink how we sanity-check a culture before moving on.