Screening and characterization of new potentially probiotic lactobacilli from breast-fed healthy babies in Pakistan

Probiotic bacteria are used for the protection and improvement of human intestinal microflora with added health effects. In search of new probiotics, 61 lactobacilli isolates were screened for survival in acidic conditions and simulated gastrointestinal juices, tolerance to ox-gall and antimicrobial activity. Selected strains (NWS09, NWS11, NWS14, NWS19 and NWS29) were identified by sequencing their 16S rRNA gene and 16S-23S rRNA gene spacer region, and further characterized by the absence of transferable antibiotic resistance, adhesion to Caco-2 cells and survival in gastrointestinal tract of BALB/c gnotobiotic. NWS09 had transferable resistance to erythromycin conferred by erm(B) gene, while NWS14 was resistant to tetracycline. NWS29, identified as Lactobacillus fermentum showed remarkable tolerance to simulated gastrointestinal juices and bile and highest antimicrobial activity against 5 food borne pathogens by producing heat (100 degrees C) and pH resistant bacteriocins. L. fermentum NWS29 was also found to be highly adhesive to human caco-2 cells in vitro as compared to NWS11 and NWS19 and was isolated in highest numbers from BALB/c gnotobiotic after 24, 48 and 72 h of orogastric inoculation. L. fermentum NWS29 was identified as a probiotic strain that can be incorporated in functional foods for human use.