That seems like the other possibility, yeah. My eye sees what looks like a meaningfully different number or density of bacterial clusters on the "detergent" sam

That seems like the other possibility, yeah. My eye sees what looks like a meaningfully different number or density of bacterial clusters on the "detergent" sample in that comparison, but I could pretty easily imagine it falling into a "close enough to be statistically indistinguishable" category. (I would have expected detergents to damage cell membranes enough to make some kind of difference, but I'll admit this is awfully far from my expertise in high-energy physics. :) )