Plasmid Profiling and Curing of Lactobacillus Strains Isolated from Fermented Milk for Probiotic Applications

In this study, the antimicrobial susceptibilities and presence of plasmids in 7 probiotics strains which had been isolated from the fermented milk were determined. Resistance to 8 commonly used antibiotics $lactans (penicillin, ampicilin), gram positive spectrum (vanomycin), broad spectrum (rifampin, trimethoprim) and aminogycosides (kanamycin, streptomycin, and bacitracin) was assessed by disk diffusion. Among these strains 20, 20, 60, 70, 90 and 100% were found to be exhibit a significant degree of resistance to kanamycin, trimetroprim, rifampicin, kanamycin, amphicilin and penicillin respectively. Further, plasmid profile and curing of plasmid were performed for the seven isolates. Analysis of the plasmid profiles of the 7 cured derivatives revealed loss of plasmids except 2 strains where curing was partially effective. All the strains lost penicillin resistance after curing indicating that plasmids encodes for resistance character. However, vanomycin resistance is not lost upon curing which indicates that such resistance is usually intrinsic (chromosomally encoded and not transmissible). Finally, the antimicrobial susceptibility after curing was done to check the safety aspect of the isolates for their application as probiotics and among the 7 strains, 5 were proved to be potent probiotics.