During my storage study with a particular type of fermented food product samples, the count of lactic acid bacteria was found to increase with storage time, which would reduce the proliferation of pathogen. However at the same time in one of the samples, after six weeks of storage Staphylococcus spp was observed to be growing and reached to a maximum at the end of storage time. What might be the possible reason?
I think food industry surfaces could thus be a suitable reservoir for S. aureus forming complex communities with undesirable bacteria in multispecies biofilms, howver, in the case of fermented foods, S. aureus can be found in the surfaces due to unhygienic conditions, but they may not found inside the food due to inhibitory substances produced during fermentation such acids, bacteriocins......etc.
according to several studies stated that some strains of S. aureus able to survive during fermentation process and some strains continue to produce endotoxin in pH medium 4.0 (Donnely et al., 1989)
This could arise from contamination from containers, hands and other equipment utilized during the experiments. Not withstanding, such strains you have identified may not be pathogenic.
If you look at fermented salami you most often use a blend of (good/non-pathogenic) staphylococci (for colour and aroma formation) and LAB for acidification. They are able to develop "side-by-side" if pH is not below 5. Staphylococci are pH sensitive and start to be inhibited at approx. pH 5.3 and stop being active at pH
Staphylococci can never grow in media with a low pH sich (no growth bellow pH 4.4). But it would depend on the nature of your samlpe. In meat products staphylococci can grow especially S. xylosus S. simulans and S. carnosus. In liquid dairy products staphylococci cannot grow because of the acidity and bacteriocins production but in cheeses some staphylococci can grow or survive at the suraface. In cereals based foods rice, soya beans etc...) Staphylocci can grow easily even if the pH is low. In olives and vegetables fermentations Staphylococci cannot grow. Please tell us the nature of your fermented food for we can help you more. All the answers from the colleagues given here are true and you might get the idea about your problem.
You should have been isolated and identified the Staph. that proliferate your product sample/s. This could be an important addition to our knowledge regarding fermentation. Fermentation is very unpredictable and the dynamics it carries add burden to quantify the microbial communities it has. I find your findings very interesting.
Try freezing the fermented food after fermentation and defrost only when you want to consume or use.
I do not know which fermented food product you investigate, for how long storage period you talk about, and whether you have added a starter culture. But in a salami/meat matrix both LAB and staphylococci grow well together and survive well during freezing. Was it Staph. aureus or other hemolytic staph. you found?
Hi
Staphylocci are very adapted to some media such as meat and vegetables but they cannot grow in liquid fermente foods. In meat products some of them are beneficial such as Staphylococcus cohni staphylococcus simulans staphylococcus xylosus. These are lipolytics and are not antigenic. But in some vegetable fermented foods they can grow just check the catalase and coagulase to know if there is a hazard in your food because of thermonuclease
More help is possible if we know the product
regards
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