MODES OF INHIBITION OF FOODBORNE NON-SALMONELLA BACTERIA BY SELENITE CYSTINE SELECTIVE BROTH

Various cell densities of six common foodborne non-Salmonella bacteria were exposed to selenite cystine (SC) Salmonella selective medium. Th e insensitivity of Pseudomonas aeruginosa and Proteus vulgaris to SC w as confirmed. Selenite cystine selective medium was effective against the sensitive bacteria up to certain cell densities, beyond which the bacteria survived. As judged from the minimum cell number required for survival in SC, Staphylococcus aureus was the most sensitive to SC, f ollowed by Bacillus cereus, Escherichia coli and Citrobacter freundii. When sensitive bacteria were grown in SC, they enriched resistant var iants which exhibited no or reduced sensitivity to SC. The change in d ensity of sensitive cells after exposure to SC suggested that bacteria l sensitivity to SC depended on the efficiency of killing and growth i nhibition by SC as well as the fraction of resistant variants in the b acterial population. Since Salmonella samples generally contain unknow n numbers and types of sensitive bacteria, it is difficult to predict the effectiveness of their selective inhibition by SC.