PRODUCTION OF HEAT AND ALKALI STABLE BACTERIOCINS BY STRESS TOLERANT PROBIOTICS FROM FAECES

A total of six probiotic strains were isolated from faecal sample of infant and calf. These strains were analyzed and partially identified by morphological (Gram staining) and biochemical (catalase, indole production, methyl red, urease, citrate utilization and H2S production) tests. All the isolates showed a broad inhibitory action against different pathogenic microorganisms including Klebsiella pneumoniae (zone of inhibition: 7-8mm), Staphylococcus epidermidis (7-8mm), Pseudomonas aeruginosa (7-8mm), Escherichia coli (8-9mm), Enterococcus faecalis (8-9mm) and Serratia marcescens (7-9mm) as exhibited by disc-diffusion method. The isolates were found to have great potential to resist a wide variety of commonly used antibiotics like amoxycillin/sulbactam, nalidixic acid, ciprofloxacin, penicillin G, norfloxacin, oxacillin, amoxycillin and ampicillin. The probiotic isolates were found to tolerate stresses like acid (pH-2.0, 3.0, 4.0, 5.0), bile salt (0.5%, 1.0%, 1.5%, 2.0% (w/v)), lysozyme (0.5 mg ml -1 ), 0.4mM hydrogen peroxide (30% (w/v)) and NaCl (1.0%, 2.0%, 4.0%, 5.0% (w/v)), thus indicating their persistence under in vivo conditions. Almost negligible haemolytic activity indicated that these probiotics were safe for human health. Moreover, the bacteriocins produced by these probiotics exhibited prominent antimicrobial activity against all the test microorganisms. Some of these bacteriocins were also found to be highly stable as they retained their activity against E. coli even at high temperatures upto 121°C and under acidic as well as alkaline conditions (pH-1.5 to 9.0). Among all the probiotic strains examined, F3 and C1 and C2 possessed most of the desirable probiotic properties and can therefore claim their potential for applications in human health.