Screening of Lactic Acid Bacteria from Various Fermented Foods for Bacteriocin Formation

Abstract

In this study, a total of forty isolates of lactic acid bacteria (LAB) were isolated from different types of fermented foods consumed in Sudan. Phenotypic tests revealed that, all isolates were homofermentative LAB. Among these, 57% were identified as enterococci, 23% as lactobacilli and 10% of them were identified as pediococci. An agar spot test was used to screen all isolates for antagonistic activities against pathogenic bacteria (Staphylococcus aureus and Escherichia coli). Twenty-four isolates were found to produce inhibitory substances primarily active against the indicator organisms used. Seventy two percent of Enterococcus isolates, 55% of Lactobacillus isolates and 25% of Pediococcus isolates were active against S. aureus and E. coli. The inhibitory activity of 88% of enterococci and 58% of lactobacilli was recorded from meat isolates, whereas all activity of pediococcal isolates came from fermented milk isolates. The cell-free cultures of 15 isolates exhibiting inhibitory activity was chosen for further investigation such as sensitivity to proteolytic enzyme (pepsin), effect of heat treatment (60oC for 60min, 100oC for 10min and 121oC for 15min ) and effect of 2 levels of pH ( pH 2 and pH 9). The inhibitory activity was eliminated upon treatment with pepsin. The bacteriocin-like substances lost activity after heating, and they were active at pH 2. At pH 9 the activity appeared to decrease