RESUMO
71 samples of milk and dairy products were collected from 18 cities throughout Iran. 93 strains of lactic acid bacteria [LAB] were isolated and assayed against four opportunistic pathogens including E. coli, proteus and klebsiella as gram-negative and S. aureus as a gram-positive organism. All indicators [organisms] were hospital strains. Among isolated bacteria, lactobacilli [37 isolates] had stronger activity against gram-negative pathogens. 37 isolates were lactococci out of which 9 strains were leuconostocs and seven strains were S.faecalis. S. aureus was more sensitive to lactococci than lactobacilli. Only one isolate of leuconostoc inhibited the growth of gram-negative indicators, but five isolates inhibited S. aureus. The use of bacteriocin-producing lactic acid bacteria in dairy products provides a natural mean of preservation