RECOVERY OF LACTIC-ACID BACTERIA ON PETRIFILM(TM) SM UNDER VARIOUS INCUBATION ATMOSPHERES

The ability of lactic cultures to grow on Petrifilm(TM) SM plates was studied. Frozen yogurt mix was analyzed microbiologically by plating o n TGE, LBS, M17 and Petrifilm(TM) SM. Plates were incubated aerobicall y in a Gas-Pak System and under a C0(2) environment. Also, Lactobacill us bulgaricus, Streptococcus thermophilus, Lactococcus lactis subsp. d iacetylactis, and Leuconostoc cre-moris were isolated from yogurt and buttermilk samples for study. Isolated cultures were grown in nutrient broth and plated on Petrifilm(TM) SM and M17 agar. Plates were incuba ted aerobically and in a Gas-Pak system. Petrifilm(TM) SM plates perfo rmed as well or better than the M17 agar in assaying lactic growth wit h the exception of Streptococcus thermophilus culture in an aerobic en vironment. Petrifilm(TM) SM plates show promise as a method for enumer ating viable lactic cultures if incubated in a reduced oxygen environm ent.