Purpose: Therefore, the objective of this study was to evaluate the effect of NaCl on antibiotic sensitivity and biofilm formation of Salmonella.
Methods: Of 10 Salmonella strains, two strains of Salmonella were selected for the highest antibiotic resistance (ciprofloxacin)/biofilm formation (Salmonella Enteritidis NCCP12243) and the lowest antibiotic resistance/biofilm formation (Salmonella Typhimurium NCCP10812). The two strains were exposed to 0, 2, and 4% NaCl supplemented in tryptic soy broth (10 ml) for 24 h at 35°C. Salmonella cells were also subjected to sequentially increased NaCl concentrations up to 4% NaCl. The Salmonella cells were then examined for antibiotic sensitivity by a disc diffusion assay; amoxycillin, chloramphenicol, ciprofloxacin, gentamicin, neomycin, oxytetracycline, streptomycin, and tigecycline. Biofilms of the NaCl-habituated Salmonella cells were quantified by crystal violet, and the biofilm cells were visualized by confocal laser scanning microscope. Major components of the biofilm matrix were also examined by Congo red assay.
Results: The relationship between antibiotic sensitivity and NaCl (0, 2, and 4%) was not observed. However, the pathogen had decreased (P < 0.05) antibiotic sensitivity to chloramphenicol, gentamicin, and oxytetracycline when S. Typhimurium NCCP10812 was exposed to sequentially increased NaCl concentration. S. Typhimurium NCCP10812 had increased (P < 0.05) biofilms, but S. Enteritidis NCCP12243 had decreased (P < 0.05) biofilms as NaCl concentration increased. Moreover, major components of Salmonella biofilms were cellulose and curli, and these components were not influenced by NaCl exposure.
Significance: These results indicate that NaCl in foods may decrease antibiotic sensitivity and biofilm formation of Salmonella.