I TA two lab sections for Medical Microbiology. My students recently learned how to do streaking for isolation using a mixed culture of S. marcescens, P. fluorescens, and C. violaceum. After picking colonies and restreaking, multiple students had no growth on their C. violaceum plates and those that did have growth had very few colonies starting with their first or second streak. The S. marcescens and P. fluorescens grew just fine. I'm somewhat at a loss to explain why this failure to grow C. violaceum occurred fairly consistently across 48 students, so if anyone could point me in the right direction, I would be glad to hear it.
Thanks!
Perhaps the following article can be useful to you:
Tryptophan synthetic pathway and its regulation in Chromobacterium violaceum
Article Tryptophan Synthetic Pathway and Its Regulation in Chromobac...
Kevin Mulkerrins .-. It sounds to me that one (or combination) of the following has occurred:
1/ The media used to prepare the plates for the second streaking was older or maybe even a different type (used NA for second round, TSA for first).
2/ The media was not mixed as well as it should have been. Or it was overheated causing breakdown.
3/ If the same set of plates were used, because they were 48 hours older and thus had dessicated some, there was not enough water for best growth (some plates also dried more than others).
Retry, using fresh and good media to see if my guesses might be correct.
Can't really retry until next semester, we have to move on to the next set of experiments for the course. More or less just asking for something to put into their lab reports (which were already submitted). I doubt that the media was old, and at any rate, it was the same set of plates and conditions that the S. marcescens and P. fluorescens grew well on. Thanks for the answers though
Kevin Mulkerrins .-. hopefully next semester will work better. But, if the same set of plates were used, they were around 48 hours older (and drier?). How were they stored during the intervening period from the first lab until the plates were used to grow the isolated colonies?
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