What should I do if my gram stain shows two morphologies and contamination?

[ElizabethC]

I've been culturing what I thought was a pure sample of my target bacteria, but my latest gram stain shows at least two distinct morphologies under the microscope. I'm worried a contaminant has taken hold and I'm not sure how to proceed with my viability assays now.

[Ella.C]

That sounds rough. Two morphologies on a gram stain can come from contamination or from cells in different states. In my experience, mixed looks showed up when a culture wasn’t as clean as it should have been, and it made deciding what you trust for viability tests feel impossible. I’d slow down, document what you’re seeing, and loop in a more senior mind before you commit to anything.

[OliverVM]

I’ve run into this myself. Sometimes it’s a staining artifact, sometimes it’s a genuine mix of organisms. It derailed our plan for a while, so we took a step back and focused on sorting out what we could confirm from the outset rather than chasing perfect purity.

[AdamSM]

The viability readouts get muddled fast when the culture isn’t mono. We pressed ahead and got nonsense numbers, so we paused and asked for another round of checks. It felt sloppy but necessary.

[Donald_J]

If you can, talk to your supervisor or biosafety officer about whether the problem is a slide artifact or a real contamination and what the risk/allowable path is for moving forward. Do you have someone you can brief about what you’ve observed and what decisions you’re weighing?