The antimicrobial and antibiofilm activity of Lactobacillus salivarius and Lactobacillus casei against Escherichia coli

Abstract

Background: Lactobacilli have been crucial for the production of fermented products for centuries. They are also members of the mutualistic microbiota present in the human gastrointestinal and urogenital tract. Recently, increasing attention has been given to their probiotic, health-promoting capacities. Objectives: The purpose of this study was to (a) evaluate the antibacterial and antibiofilm activities of Lactobacillus salivarius (ATCC 11741) and Lactobacillus casei (ATCC 9595) against Escherichia coli; and (b) assess the anti-virulence potential of these probiotics, by examining their impacts on the expression of selected genes in the test organism. Materials and Methods: The antibacterial, antibiofilm and antivirulence activities of L. salivarius and L. casei against E. coli were investigated by agar well diffusion, microtiter plate, crystal violet assay, quantitative real-time polymerase chain reaction (qPCR) analysis. Results: Susceptibility testing indicated antibacterial and antibiofilm activities of L. salivarius and L. casei against E. coli. Agar inhibition assay showed that L. salivarius and L. casei has antibacterial activity against E. coli with an inhibition zone of 21±2 mm and 24±1 mm respectively. The L. salivarius and L. casei were found to degrade and inhibit E. coli biofilm. All biofilm-forming cells treated with L. salivarius and L. casei supernatants showed reduced expression of genes involved in biofilm formation and quorum sensing. The expression of yjfO (bsmA), csgA, ycfR (BhsA), tnaA, lsrA, and rpoS genes of E.  coli was decreased, 0.75-fold, 0.65-fold, 0.5-fold, 0.73-fold, 1.2-fold and 0.85-fold respectively after exposure to L. salivarius, while the expression of yjfO (bsmA), csgA, ycfR (BhsA), tnaA, lsrA, and rpoS genes of E.  coli was decreased, 1.0-fold, 0.75-fold, 0.5-fold, 0.82-fold, 1.4-fold and 0.9-fold respectively after exposure to L. casei. Conclusion: The results of this study indicate that L. salivarius and L. casei strains showed a good antibacterial and antibiofilm against E. coli. Generally, present study suggested that the L. salivarius and L. casei strains exhibits a good antimicrobial activity.