Effects of cell-free supernatant of Lactobacillus acidophilus LA5 and Lactobacillus casei 431 against planktonic form and biofilm of Staphylococcus aureus

This study was carried out to investigate the stability, antibacterial properties and biofilm removal potential of cell-free supernatant (CFS) of Lactobacillus acidophilus LA5 and Lactobacillus casei 431 against Staphylococcus aureus ATCC 25923. Antibacterial activity of both Lactobacillus strains was measured according to the agar spot method. The CFS was prepared by centrifugation of bacterial suspension at 4000 g for 10 min and the antimicrobial activity was measured using agar-well diffusion. The stability of CFSs during storage at 4.00 ± 2.00 °C and 25.00 ± 2.00 °C for a period of 4 weeks was measured based on the method of broth micro-dilution assay. Moreover, biofilm removal potential of CFS on 2-days-old biofilm of S. aureus­ developed on polystyrene and glass surfaces was also determined. The efficacy of CFS on bacterial biofilm established on the glass surface was also observed using fluorescence microscope. Results showed that inhibition zones of L. acidophilus (50.26 mm) were greater than L. casei (37.06 mm). The minimum inhibitory concentration of both CFSs remained stable (40 mg mL-1) during the storage for 28 days at 4.00 and 25.00 °C and storage temperature did not affect the antibacterial effectiveness of CFS. The addition of both CFSs significantly removed biofilm developed on both tested surfaces in a concentration-dependent manner. Biofilm removal property of L. acidophilus CFS was generally better than L. casei CFS which was confirmed by fluorescence microscope. The application of CFS of probiotic strains (i.e. Lactobacillus) as antibacterial and biofilm removal compounds could be very suitable to control the growth of food-borne pathogens.