As the selectivity of this medium is low and contaminants tend to grow subculturing in a (double layer) solid medium, and then in
broth is recommended to increase selectivity. In many cases, growth is encouraged by incubation in a CO2 enriched atmosphere.
MRS medium is particularly recommended for the enumeration and maintenance of lactobacilli either by the MPN technique in broth,
(Art. No. 02-135) or by inoculation on a plate, overlaying it with a second layer of molten medium. This technique overcomes the
need for a CO2 enriched atmosphere.