Yasmeen Y. A. Elyas, Nuha M. E. Yousif, Isam A. Mohamed Ahmed
Microbiology of Microbiology
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. Twenty-four isolates produced inhibitory substances primarily active against Staphylococcus aureus ATCC 2818 and Escherichia coli ATCC 29522. 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 18 isolates exhibiting inhibitory activity was chosen for further investigation such as sensitivity to proteolytic enzyme (pepsin), effect of heat treatment (60°C for 60min, 100°C for 20min and 121°C for 15min) and effect of pH ( pH 2.0, pH 6.5, and pH 9.0). The inhibitory activity was eliminated upon treatment with pepsin. The bacteriocin-like substances lost their activity after heating at all temperatures used and at alkaline pH (9.0), whereas they were active at acidic pH (2.0). The antimicrobial activity of bacteriocin-like substances produced by the isolated LAB could prevent spoilage and/or pathogenic microorganism in Sudanese fermented food. Further study should be related with species identification of the producer strains and with the purification and characterization of these becteriocin-like substances in order to explore them in food industry.