CHARACTERISTICS OF BIOFILM FORMATION BY SELECTED FOODBORNE PATHOGENS

ABSTRACT Strains of Listeria monocytogenes, Serratia liquefaciens, Shigella boydii, Staphylococcus aureus, Salmonella Enteritidis, and Bacillus cereus were used to evaluate bacterial biofilm‐forming ability in trypticase soy broth (TSB; pH 6 and pH 7) at 37C. The biofilm development was determined by using the crystal violet method and the degree of biofilm formation was expressed as the specific biofilm formation (SBF) index. Among all strains tested, L. monocytogenes and S. liquefaciens formed strong biofilms in half‐strength TSB (pH 6), showing 2.79 and 3.85 of SBF indices, respectively. The numbers of adhered L. monocytogenes and S. liquefaciens increased to 7.57 and 7.91 cfu/slide, respectively, after 36 h. The increase in the biofilm formation of L. monocytogenes and S. liquefaciens was shown in the scanning electron microscopy micrographs. The protein profile differences were observed between biofilms and planktonic cells, suggesting that biofilm‐specific protein expression is involved in the biofilm development. PRACTICAL APPLICATIONS Since the biofilm formation has been a major concern to the food processors and medical devices, it is worthwhile to characterize the biofilm formation of foodborne pathogens under food processing‐related stress conditions. The results suggest that foodborne pathogens have distinctive patterns of biofilm formation. Therefore, it might be useful information to better understand the mechanism of biofilm formation in different environmental conditions and evaluate the infectivity and pathogenicity of biofilm‐forming foodborne pathogens.