The Antimicrobial Effects Of Bacteriocins Extracted From Some Lactobacilli

In this study two species of Lactobacillus were isolated and identified. They were Lactobacillus plantarum from cheese and Lactobacillus casei from yoghurt. Then they were screened for their antimicrobial activity. Bacteriocins produced by the two species were extracted and tested against 5 reference bacterial strains, two gram-positive bacteria (Bacillus subtilis and Staphyloccous aureus) and three gramnegative bacteria (Escherichia coli, Proteus vulgarus and Pseudomonas aeruginosa) and 59 clinical isolates. Antimicrobial activity was determined by Diffusion methods (Disc and Cup plate method), minimum inhibitory concentration method (MIC) and agar spot method. Two bacteriocins exhibited inhibitory activity against 5 reference strains and most of clinical isolates excpet Kurthia spp. Proteus vulgaris, S. aureus and S. epidermis were the most susceptible to Lact. casei bacteriocin while E. coli, Salmonella typhi and Serratia pymthca were the least susceptible to it. Proteus vulgaris, S. aureus, S. epidermis, Bacillus subtilis and Candida albicans were the most susceptible to the bacteriocin of Lact. plantarum, while E. coli, Salmonella typhi and Serratia pymthca showed the least susceptibility to it. Kurthia spp. was resistant to both bacteriocins. Bacteriocin produced by Lact. plantarum was more active than that produced by Lact. casei because inhibition zone was wider than those produced by Lact. casei bacteriocin. The minimum inhibition concentration for Lact. plantarum bacteriocin was 1/64 while the minimum inhibition concentration for Lact. casei bacteriocin was 1/32