Antibacterial Bioactivity of Some Lactic Acid Bacteria Isolated from Various Egyptian Products

Abstract

The current research aimed to isolate and screening of antibacterial bioactive lactic acid bacteria (LAB) from different foods such as raw milk, dairy products and fermented meat and evaluate their potential for production of antibacterial substances, namely bacteriocins. Ten samples were collected from different market foods, examined and used for LAB isolation on MRS medium. A total of 71 bacterial isolates were selected based on some variation properties, such as color, shape, size and oxygen requirements. These isolates were confirmed as lactic acid bacteria based on their microscopic observation and chemical properties, i.e. catalase negative and acid producing from glucose fermentation. All selected isolates were grown on MRS medium at 37oC for 48 h, and compared to identified LAB strains, i.e. Lactococcus lactis, Streptococcus thermophilus, Befidobacterium sp, Lactobacillus casi, Lb rhamnosus, Lb. acidophilus, Lb. helveticus and Lb. plantarum. Isolates and strains were surveyed for bacteriocin production as inhibitory activity test. Partial purification of bacteriocin was carried out by salt precipitation method; this method was done by ammonium sulphate 40-60% saturation and centrifuged at 9500 rpm for 20 minutes at 4oC. Some of microbial indicator strains found to test by inhibitory biological activity substance (partial purification of bacteriocin) produced by lactic acid cultures. Indicator strains such as staphylococcus aureus, Listeria monocytogenes and others were grown by nutrient agar at 37o C for 24h. An inhibitory activity test was executed by paper diffusion method. The inhibition effect was examined by form clear inhibition zone around indicator strains. Twenty-eight isolates and the 8 LAB strains showed bioactivities against the tested pathogens. Gram positive indicator bacteria were found to be the most sensitive to inhibitory substances produced by LAB culture as compared to gram negative indicator strains. Staphylococcus aureus was exhibited the highest sensitivity to it. The highest bacteriocins activities were produced by strain Lactobacillus rhamnosus while R5 and S6 from LAB isolates. They were shown broad spectrum against gram positive and gram-negative pathogenic bacteria. Diameters of inhibition zone refer to degree of sensitive between indicator strains and bacteriocin activity