Background: Pseudomonas aeruginosa, as an important opportunistic pathogen, can produce P. aeruginosa. biofilm. Intrinsically resistant to antimicrobial agent, the biofilm causes difficulties in various healthcare settings. Lactobacilli are known to secrete inhibitory substances in cell-free supernatant (CFS) to prevent infection by pathogenic organisms. The purpose of this study was to evaluate the inhibitory effects of CFS from Lactobacillus casei PTCC: 1608 on biofilm formation of P. aeruginosa PTCC: 1430.

Materials and Methods: In this experimental study, CFS from Lactobacillus was separated by centrifugation. The antimicrobial effect of CFS from L. casei was evaluated by agar well diffusion assay. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by microdilution method according to CLSL standard. Finally, biofilm-production ability of P. aeruginosa as a percentage was determined in the presence of CFS from L. casei using the modified microtiter plate method.

Results: Results showed that CFS from L. casei has a significant effect on the tested strain and the MIC and MBC values for the strain were the same (62.5 µl ⁄ ml). Furthermore, in the presence of CFS from L. casei, biofilm production in MIC (87±2.6) and Sub-MIC concentration was considerably inhibited.

Conclusion: CFS from L. casei is effective in killing P. aeruginosa. biofilm. Therefore, this material appears to be a promising agent for prophylaxis against various pseudomonal infections.