Isolation and identification of probiotic lactic acid bacteria from curd and in vitro evaluation of its growth inhibition activities against pathogenic bacteria

The aim of this study was to isolate and identify probiotic lactic acid bacteria from curd and evaluate in vitro, its growth inhibition activities against pathogenic bacteria. A total of nine strains of Lactobacillus were isolated from curd and identification of strains was done by biochemical and physiological tests and Lactobacillus leichmannii, Lactobacillus casei, Lactobacillus delbrueckii, Lactobacillus brevis, Lactobacillus fermentum, Lactobacillus coagulans, Lactobacillus acidophilus, Lactobacillus lactis and Lactobacillus rhamnosus strains were identified from curd. Lactobacillus strains survival were also assessed under conditions simulating human GI tract. Therefore, resistance to antibiotics, resistance to low pH, resistance to bile salt and bile salt hydrolysis was performed. Results showed that all tested isolates were able to grow at low pH 3.0, and at 0.3% bile concentration. L. casei, L. delbrueckii and L. brevis showed more resistance to antibiotics. According to haemolytic activity, all examined strains did not exhibit β-haemolytic activity when grown in Columbia human blood agar. Regarding the bile salt hydrolysis, L. casei and L. delbruekii showed partial bile salt hydrolysis activity and colony morphology was recorded as differentiated in comparison with the control MRS agar plates. Finally, antimicrobial activities of lactobacillus isolates were tested against five pathogenic bacteria (Staphylococcus sp., Bacillus sp., Klebsiella sp., Pseudomonas sp. and E. coli sp.) at pH 6.5 by disc diffusion method. All the tested isolates showed in vitro inhibitory zone against pathogenic bacteria. L. casei and L. delbrueckii showed maximum inhibition zone. In conclusion, the present study showed that L. casei and L. delbrueckii can be used as potential probiotic lactic acid bacteria.   Key words: Lactobacillus, curd, probiotics, antibiotic resistance, resistance to low pH, resistance to bile, pathogenic bacteria.