growth inhibition of pathogens by lactic acid bacteria producing inhibitory substances

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 patho gens 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.jaecalis. 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.