We often find Salmonella in fish meal (dry sample with around 6 % moisture and 9 % fat) samples but after a while (a week or two) the levels drop so low that we cannot detect it anymore. Is there a way to keep the Salmonella viable for a longer period? We would like to use this naturally contaminated feed to spike other feed to use in research projects over a period of time. Would refrigerating or freezing the sample help? Could I use some sort of cryoprotectant?
Normally salmonella would survive on higher moisture contents. Even addition of some water or saline would work.
Thanks Muahammad Tanveer Munir . We would also like to increase the amount of Salmonella in the sample. I thought at first to add Buffered peptone water (BPW) to the fish meal but I realise that this would also increase the background flora. Do you think I could add a selective broth such as Rappaport Vassiliadis Soya Broth (RVS Broth) to the fish meal or would it be too harsh on any injured Salmonella cells? Perhaps add some BPW and incubate overnight and then add RVS broth the next day?
Or simply, grow salmonella in separate broth and add in pure form... They higher quantity may suppress the growth of other competitive flora...
Thanks Muahammad Tanveer Munir . We tried artificially contaminating feed in that way in previous experiment but the results were not as expected (a 37 % formaldehyde solution added to the feed did not bring the counts down as low as expected) in that experiment .
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