Isolation of acidophilic lactic acid bacteria antagonistic to microbial contaminants

Four species of lactic acid bacteria viz. l. bulgaricus,l. casei,l. acidophilus and l. salivarius were isolated from a local yogurt sample. the bacterium l. salivarius showed maximum growth at 37°c with initial ph 6. l. bulgaricus and l. acidophilus also grew best at 37°c but with initial ph 4.the bacterium l. casei showed maximum growth at 25°c at ph 5. all the four bacteria formed smooth textured and white yogurt at 2% inoculum. l. acidophilus tolerated acid upto 1 ph. however,l. bulgaricus and l. salivarius showed more resistance to acia when cultured in yogurt as compared to their cultivations in the selective medium. these lactic acid bacteria demonstrated antimicrobial activity against different isolates of e. coli,staphylococcus sp.,salmonella sp. and yeasts. the l. acidophilus was found to be the most potent antagonistic microbe against e. coli,while the isolate l. bulgaricus expressed vivid antifungal activity. acid tolerance,yogurt fermentation and bacterial and fungal antagonistic characteristics of these bacterial isolates render them good candidates for their consideration as probiotics. copyright 2010 zoological society of pakistan.