Biofilm formation, slime production, and antibiotic susceptibility properties of the Bacillus cereus group isolated from fresh vegetables in the Republic of Korea

This study aimed to characterize the ability of the Bacillus cereus group isolated from conventionally, organically or pesticide-freely grown vegetables to form biofilms with regard to cell surface hydrophobicity (CSH), slime production, and antibiotic susceptibility. Cellular properties (biofilm formation, CSH, and slime production) were measured using an in vitro microplate assay with crystal violet staining, adhesion to hydrocarbons assay, and Congo red broth method, respectively. Consequently, 16, 16, and 16 B. cereus strains were isolated from conventionally, organically, and pesticide-freely grown vegetables, respectively, and 16 (33%) B. cereus isolates were highly biofilm-positive producers. CSH values dramatically varied, ranging from 19 to 74%, among the B. cereus isolates. Additionally, 9, 8, and 8 B. cereus strains isolated from conventionally, organically, and pesticide-freely grown vegetables, respectively, were identified to be slime-positive producers. According to the disc diffusion method, 19 and 41 B. cereus isolates were highly resistant to ampicillin and penicillin, respectively.