Effect of plating and incubation conditions on the detection of lactic acid bacteria after high hydrostatic pressure treatment

Lactic acid bacteria (Leuconostoc mesenteroides, Enterococcus faecalis, and Lactobacillus fermentum) were subjected to high hydrostatic pressures (HHPs) of 400 and 600MPa at 25 degrees C for 10min in phosphate-buffered saline. Differential plating methods were applied to evaluate HHP-treated cell populations, assuming that healthy and injured cells during plate incubation survived maximum and minimal stress, respectively. The stress was altered by using several selective media in combination with aerobic or anaerobic incubation at 25 degrees C or 30 degrees C. E.faecalis was detectable after 600MPa treatment while L.mesenteroides and L.fermentum were nondetectable. Specific combinations of incubation conditions were suggested to determine maximum and minimum viable counts of L.mesenteroides and E.faecalis. The difference between the maximum and minimum counts can be used to evaluate HHP-injured population with reduced risks to overestimate healthy and/or underestimate HHP-injured cells.