Lactic acid bacteria from kefir grains: Potential probiotics with antagonistic activity against multidrug resistant Gram-negative bacteria

Aims: This study aimed to isolate and identify lactobacilli strains that have antagonistic activity against multidrug resistant (MDR) isolates of Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa and evaluate their probiotic properties. Methodology and results: Twenty-one Lactobacillus isolates were collected, and their antimicrobial activity was assessed by agar well diffusion, broth microdilution and time-kill test. The probiotic potential of the isolates was evaluated as well. The bacterial culture and cell free supernatant (CFS) of all isolates exhibited antibacterial activity against all MDR isolates. Out of 21 isolates, 4 isolates (A31, B35, S20 and S25) displayed the highest antimicrobial activity and further evaluated. The minimum inhibitory percentages of CFS from selected isolates against pathogens ranged from 10 to 30% and the bactericidal percentages ranged from 20 to 50%. The inhibitory activity of CFS was not changed after heating but abrogated as the pH neutralized. The growth kinetic of the MDR pathogens was significantly reduced in the presence of the CFS of all isolates. The isolates had a less than 1-log reduction in their viability in acid tolerance test and could grow in the presence of 0.3% bile salts. Strains S20, S25 and B35 exhibited high co-aggregation with E. coli (51.7-73.3%), P. aeruginosa (53.7-69.3%) and K. pneumoniae (49.7-65.3%). Molecular identification revealed that the isolates were Lactobacillus rhamnosus (B35) and Lactobacillus paracasei (S20, S25, A31). Conclusion, significance and impact of study: The results suggest that these lactobacilli isolates may have potential applications for controlling and preventing colonization of infections caused by MDR pathogens.