Abstract
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.
Highlights
The term probiotic, literally meaning “for life”, was first addressed by Lilly and Stillwell (1965) and was used to describe substances produced by protozoa to stimulate the growth of other organisms
Lactic acid bacteria were isolated from curd obtained from different sources of dairy products
MRS medium containing 0.3% (w/v) bile concentration was inoculated with overnight culture of lactic acid bacteria
Summary
The term probiotic, literally meaning “for life”, was first addressed by Lilly and Stillwell (1965) and was used to describe substances produced by protozoa to stimulate the growth of other organisms. Intake of probiotics stimulates the growth of beneficial microorganisms and reduces the amount of pathogens, improving the intestinal microbial balance of the host and lowering the risk of gastro-intestinal diseases (Fuller, 1989; Cross, 2002; Chiang and Pan, 2012). Their benefits include the alleviation of certain intolerances (such as lactose intolerance), the enhancement of nutrients bioavailability, and prevention or reduction of the prevalence of allergies in susceptible individuals (Isolauri, 2001; Chiang and Pan, 2012). Probiotics are reported to have antimutagenic, anticarcinogenic, hypocholesterolemic, antihypertensive, anti-osteoporosis and immuno-modulatory effects (Chiang and Pan, 2012)
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