Australia's Science Forum

Hi brains-trust......I'm hoping someone can help....we've been testing the effect of household cleaners on bacterial growth, & I brewed up a nice Bacillus broth with peppercorns (thanks Ian for the recipe), but for some reason the zones of inhibition are a bit strange this time.
There are 2 zones, the first a clear one with no bacterial growth (circled in red), but there's also a second zone where there's still the pale fuzzy growth through the agar (I inoculate by pouring broth into cooled liquid agar before pouring the plates), but no individual colonies (as shown outside the area circled in green).

It's a bit frustrating because there's definite inhibition in the small zone, but partial in the larger one because the colonies have failed to grow......does your Baccilus grow like mine, a combination of fuzzy 'lawn' & also a smattering of colonies?

Thoughts please?

The "fuzzy" growth could be a fungal growth perhaps from contamination

it could be that you got "bacterial lawn" (there are no distinct colonies) you maybe plated too much, it is better to be "stingy" when platting than to put too much

see this prac
http://www.d.umn.edu/~lshannon/biol1012 ... ia_001.pdf

Without being able to see the plate, I would say by the way you have made it you have a even, confluent growth over the whole plate (eg a lawn plate) and the individual colonies around the outside are in fact contamination.

But I would have to see the plate in real life to confirm this