Dear all researchers, I was facing a problem during subculturing L. gasseri and L. fermentum in MRS broth. After 3 days incubation, the broth itself become cloudy and sticky. Gasses was formed and spill out when open the cap. When the culture transferred into milk, the lactic acid was form at the bottom and gasses was pushing the milk culture to the top. May I know is the culture become contaminated? Is this their growing characteristics? Please advice. Tq.
Some lactobacilli are heterofermentative and produces a large amount of CO2 that if accumulates can spill out the cap of the culture tube.
Was this a mixed culture fermentation - or mono-cultures? These organisms can produce CO2 and extracellular polysacharides; depending on the specific isolate. As far contamination, I suggest plating the cultures and make sure of the uniformity of the colony morphology, Gram Stain should be G+, and negative catalase activity.
I feel there is some form contamination, which you need to rule out by pour plating. This overflow appears to be heterofermentative lactics so better check for the purity.
This cuestion is asociated to the heterofermentative metabolism. However, is necessary to repair the incubation conditions such as the pH, oxygen pressure and temperature.
The isolates are the lactobacillus species because they were grow in MRS media. I suggest you culturing each isolates on MRS agar with 0.5% CaCO3 to more assurance as Lactobacillus genus. The Sticky characterize I think referred for Leuconostoc species.
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