Fifi M. Reda, Basma M. Hussein and Gamal Enan
Department of Botany and Microbiology, Faculty of Science, Zagazig University, Zagazig, Egypt.
This study focused on selection and characterization of lactic acid bacteria (LAB) strains to be used as starter and protective culture for food fermentations. Thirty LAB isolates were isolated from different fermented foods onto MRS agar medium. Two LAB isolates only CK21 and PP17 showed the highest medium acidification values pH 3.2 and 3.6 respectively and inhibited many Gram positive and Gram negative pathogenic bacteria. CK21 and PP17 isolates were selected due to their desired properties to be used as starter cultures. Based on biochemical properties as well as sequences of 16S rRNA genes, CK21 and PP17 isolates were identified as belonging to Entercoccus faecium CK21 (E.faecium) and Lactobacillus fermentum PP17 (L.fermentum) . Both strains tolerated NaCl up to 10%, bile salt up to 3% and pancreatin up to 2%. Also, these strains have the ability to grow at wide pH range (2-9) and temperature range (20-50°C). These strains inhibited many pathogenic bacteria such as Bacillus cereus (B.cereus), Streptococcus pyogens (S.pyogens), Staphylococcus aureus (S.aureus), Escherichia coli (E.coli), Listeria monocytogens (L.moncytogens), Acinetobacter baumanii (A.baumanii) and Salmonela typhimurium (S.typh). The antibacterial compound from culture supernatants of both strains was found to be proteinacious in nature, heat stable at 100ºC for 30min, and active over a wide pH ranges (2-8). All this characters coupled with the definitions of bacteriocins, so the antibacterial compound could be classified as bacteriocin. Both cell free supernatants (CFS) and neutralized CFS (NCFS) of lactic acid bacterial strains CK21 and PP17 inhibited E.coli and S.pyogenes distinctively in vitro.
Keywords: Lactic acid bacteria (LAB), Starter cultures, Probiotics, Food, Bacterial pathogens.