In the new batches of media I made, both H. influenzae and E. coli grew in A (our Difco BHI) and in C (borrowed BHI) and D (old HI). They didn't grow at all in B (MBP BHI). Reinoculation of media from these bottles by one of the post-docs and by me (using independent H. influenzae stocks) gave good growth in A, C and D but not B.
But there was surprising contamination in both our cultures. Surprising because previous uses of the identical stocks had no contamination, and the no-cells controls showed no contamination in two control media (indicating that my hemin and NAD supplements were uncontaminated. And an agar-plate streak of my H. influenzae inoculum showed no evidence of contamination. Even the contaminants couldn't grow in medium B, but this would make better sense if another post-doc hadn't previously found that H. influenzae grows just fine in MBP BHI.
To test whether the identify of the person doing the preparation matters, another post-doc made media that should have been identical to my new A, B, C and D. But H. influenzae grew in all of these batches, even the MBP BHI. We can now (almost) conclude that growth results are reproducible for any specific bottle of media we prepare, but not for different preparations made from the same powder. (I write 'almost' because of a couple of pesky exceptions observed last week.)
I'm wondering if there's something wrong with our clean bottles....
Why are unfalsifiable beliefs so attractive?
2 days ago in Epiphenom