Abstract
Background: The emergence of horizontally transferable antibiotic resistance (AR) in probiotic strains of lactic acid bacteria (LAB) has incited a need to establish stringent safety measures for the assessment of commercial probiotics. Lactobacillus rhamnosus is not only a prevalent constituent of commercially available probiotics but also has an abundant presence in fermented foods.
 Methodology: The present study tested antimicrobial activity and antibiotic susceptibility of L. rhamnosus isolated from fermented cabbage. Agar well diffusion assay was used to determine the antibacterial activity against a number of Gram-positive and Gram-negative bacteria, and antibiotic susceptibility testing was used to determine the antibiogram of several antibiotics. For this, the neutralized Cell-Free Supernatant (nCFS) of L. rhamnosus was used, which exhibited antibacterial activity against several bacteria. 
 Results: Antagonistic activity of nCFS of L. rhamnosus was found against Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Vibrio parahaemolyticus, Salmonella typhimurium, Klebsiella pneumoniae, Salmonella enterica. Maximum inhibitory activity was observed against Listeria monocytogenes. Whereas, no activity was found against Staphylococcus epidermidis, Streptococcus pyogenes, Bacillus subtilis, Vibrio alginolyticus, Proteus mirabilis and Proteus vulgaris. The intensity of inhibition among the isolates was in the sequence of Listeria monocytogenes > Escherichia coli > Bacillus cereus > Vibrio parahaemolyticus > Salmonella typhimurium. L. rhamnosus was found susceptible against Chloramphenicol and Novobiocin. Moreover, it exhibited resistance to Amoxicillin, Levofloxacin, Oxacillin, Streptomycin and Tobramycin.
 Conclusion: In conclusion, this study suggests that the use of L. rhamnosus as a probiotic requires extensive examination of AR genes present in this strain.
Highlights
The ever-increasing prevalence of microbial resistance to antibiotics is becoming a public health crisis
Total 17 indicator organisms were used in agar well diffusion assay, out of which 5 were American type culture collection (ATCC) food isolates while the remaining 12 were clinical isolates
Previous studies reported higher antimicrobial activity against gram-positive bacteria[4,7], which is due to the bactericidal effect of protease, as it was elaborated by De Vuyst[8] whereas, the lack of activity against gram-negative bacteria is due to the presence of hydrogen peroxide[9]
Summary
The ever-increasing prevalence of microbial resistance to antibiotics is becoming a public health crisis. Research has revealed the LAB's efficacy as a probiotic; its effects range from growth inhibition of pathogenic bacteria to strengthening the immune response and more[4]. This perception has led to the overwhelming growth of probiotic usage from being limited to merely dairy and fermented products to largescale incorporation of probiotics in fortified foods, dairy products and health supplements[5]. Results: Antagonistic activity of nCFS of L. rhamnosus was found against Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Vibrio parahaemolyticus, Salmonella typhimurium, Klebsiella pneumoniae, Salmonella enterica. Conclusion: In conclusion, this study suggests that the use of L. rhamnosus as a probiotic requires extensive examination of AR genes present in this strain
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