I want to culture the different lactic acid bacteria that are present in fermented vegetables, i saw that MRS medium is mostly selective for lactobacillus, but there are many more types of bacteria present in the fermented vegetables. Would it be possible to grow the whole array by simply removing sodium acetate? How big is the risk of contamination from other sources?
I took this direct from one of the directions for using MRS agar:
"Lactobacilli MRS Agar is used for the cultivation of lactobacilli and is not intended for use in the diagnosis of disease or other conditions in humans. MRS Agar is a medium for the cultivation and enumeration of Lactobacillus spp. Originally developed in 1960 by de Man, Rogosa & Sharpe, the medium is suitable for most lactic acid bacteria and is intended as a substitute for Tomato Juice Agar. When acidified to pH 5.4 MRS Agar can be used to enumerate Lactobacillus bulgaricus in yogurts. Nutrition is provided by a mixture of carefully selected peptones, glucose, beef & yeast extracts while Tween® 80, magnesium and manganese sulfates act as growth stimulants. Selectivity against streptococci & molds is provided by ammonium citrate and sodium acetate. Used at low pH, ammonium citrate allows growth of lactobacilli while inhibiting a number of other microorganism groups. Occasionally, sterilization of this medium at 121°C for 15 minutes, in some autoclaves, may cause the pH to fall outside of the specified pH limits 6.4 +/- 0.2. In these rare cases, adjustment of the medium using acetic acid or sodium hydroxide is recommended."
As you can see taking out sodium acetate will leave ammonium citrate in there as a selective agent. You would have to take both of them out but you then risk getting moulds. Considering the pKa of lactic acid to be about 3.8. I would think using a medium like Muller Hinton but adjusting the pH to about 4.5 and temperature 40 to 45 degrees would select for lactic acid bacteria.
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