In vitro Screening of Lactobacillus species from Homemade Yoghurt for Antagonistic Effects against Common Bacterial Pathogens

Four species of lactic acid bacteria (LAB) were isolated from homemade yoghurt samples and defined as Lactobacillus acidophilus Lactobacillus bulgaricus, Lactobacillus casei, and Lactobacillus plantarum. Each LAB isolate was tested for its tolerance to acidic environments at pH (7.0, 4.0, and 2.0). All lactobacilli isolated tolerated acid while L. bulgaricus was sensitive to pH 2.0. All four bacteria were resistant to ciprofloxacin. Isolates were further tested for their antimicrobial activity against common pathogenic bacteria such as Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus aureus (MRSA), and Bacillus subtilis using the agar spot method. These lactic acid bacteria were found to inhibit growth of most pathogens tested. The viability of lactobacilli isolates were not affected by storage (for 6 weeks) at -20°C and 4°C but declined when they were stored at room temperature. Acid tolerance and bacterial antagonistic characteristics of these LAB isolates render them good candidates for consideration as probiotics.