The Season Effects and Shearing Time on Isolation, Identification and Genetic characterization of the bacteriocin producing lactic acid bacteria isolated from food products, and their role as a biological preservative

Lactic acid bacteria (LAB) are a divers group of gram positive bacilli, coccobacilli or cocci distributed abundantly in nature. They are found in food products including meat, vegetables, fruits, bakery and dairy products. Morever they are also present in the intestinal system of man and animals.!n this research initially 66 lactic acid bacteria were isolated from 177 dairy samples including milk and cheese and their antibacterial activity against each other and some pathogenic bacteria was evaluation under different physical conditions and methods. The results indicated 26 isolates to be inhibitory towards some of the other pathogenic bacteria and their antibacterial spectrum was shown against some gram positive and gram negative bacteria. The mode of action of each of the strain had its own pattern as indicated by their spectrum of activity against individual indicator strains. The influence of various factors including the effect of glycolytic, lipolytic and proteolytic enzymes such as lysozyme, lipase,proteases and catalase was checked on the anti bacterial activity of these isolates.Out of 26 isolates demonstrating antagonistic activity only 18 of them were sensitive of proteolytic enzymes and hence it could give a preliminary indication of the presence of bacteriocins or bacteriocin like compounds for these activities. the proteolytic against were partially purified by ammonium sulphate precipitation and then analyzed on SOS-PAGE. The results indicated different patterns specific of each isolates studied. The PH and temperature sensitivity of each of the isolates were also studied and most of the isolates retained their antibacterial potential at Iow pH values while pH values of 8.0 and above were inhibitory for all of them. The temperature resistance of the bacteriocins demonstrated by these strains indicated heat stability of LM 13 as it resisted 100C for 15min. All the bacteriocins producing strains were identified to species level by their gram reaction, catalase test and biochemical fermentation patterns. To evaluate the efficacy of the bacteriocine in controlling the growth of pathogens in cheese a number of cheese sample made under sterile conditions were incubated at 4 and 37C with and without added bacteriocin and Lmonocytogenes. according to the results the bacteriocin produced by LM13 was able to control the groeth of Lmonocytogenes in the cheese samples during a month of storage at the mentioned temperatures.Finally to evaluate the genetic characteristics of the bacteriocin produced by LM13 efforts were made to locate the bacteriocin genes of this strain. The Echardt gel electrophoresis of the strain indicated the presence of a single large plasmid which was lost in the cured strains. All the results indicated plasmid associated bacteriocin production in LM13. the approximate molecular weight of the plasmid was 42Kbp.