الفهرس 
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Abstract
The present study was carried out for the isolation of a bacteriocin producing bacteria from natural and clinical sources to study the characteristics of their bacteriocin as antibacterial agent. Bacterial isolates (102) were collected from yoghurt , wheat , maltbarly, meat, apricot, cucumber, strawberry, peach , milk, cheese, cream and new born infant faeces .The recovered isolates were subjected to different biochemical tests for identification to the species level. The isolates were also tested for determination of the level of the bacteriocin produced. The results were summarized as the following: 1 - A total of 102 bacterial isolates were recovered and out of these only 86 isolates showed different morphologies and produced yellow colour during cultivation on MRS medium containing bromocresol green that indicated the production of lactic acid and the producer is a lactic acid bacteria. Out of the above isolates, Lactobacillus Y18 was chosen as the highest bacteriocin producing bacterium and Streptococcus salivarius 5 was used as indicator strain. 2-The results obtained from morphological, physiological and biochemical tests showed that the bacterial isolate was identified as Lactobacillus plantarum SR18 and the produced bacteriocin named as plantarcin SR18. 3- On studying the growth conditions, the data revealed that the production of plantarcin SR18 could be enhanced by W irradiation.