Genotypic and phenotypic characteristics of biofilm formation of emetic toxin producing Bacillus cereus strains

The objectives of this study were: 1) to determine biofilm formation abilities of 11 emetic toxin producing Bacillus cereus strains along with two reference strains ATCC 14579 and KCTC 13153 on stainless steel and plastic coupons; 2) to examine the correlation between biofilm formation ability and genotypic and phenotypic characteristics of four selected strains. Crystal violet assay results indicated that the biofilm formation behavior was highly variable depending on strain and surface. Cell enumeration and scanning electron microscopy (SEM) analysis showed complex cell clusters with extracellular polymeric substances (EPS) for high biofilm forming strains and single layer of cell clusters with few EPS for low biofilm forming strains. Phenotypic characteristics of planktonically grown cells such as hydrophobicity were positively correlated with biofilm formation behavior. However, antibiotic susceptibility of B. cereus strains was not correlated with biofilm formation, although resistance to benzalkonium chloride showed a clear correlation with biofilm formation ability. Expression levels of two genes spo0A and abrB involved in the regulation of cell differentiation and mobility of B. cereus were positively correlated with biofilm formation. Results of this study indicate that multiple factors are involved in biofilm formation by emetic toxin producing B. cereus.