Introduction : Bacillus cereus spores are highly resistant to adverse treatments such as high temperature, radiation and chemicals. In addition, recent studies suggested that use of decontamination agents may increase antimicrobial resistance of foodborne pathogens.
Purpose: The objective of this study was to compare growth and resistant patterns of Bacillus cereus isolates obtained from different antimicrobial applications.
Methods: B. cereus isolates (S-BC-50 and S-BC-52: isolates from 10% NaClO application, S-BC-23 and S-BC-48: isolates from 0.5% H2O2 application, S-BC-54 and S-BC-56: isolates from 1.0% acetic acid application), and B. cereus KCTC1661 (standard strain) were inoculated into typtic soy broth (TSB), and incubated at 7, 10, 15, 25, 30 and 35 oC for comparison of growth pattern. To compare antimicrobial resistance of B. cereus isolates, exponential and stationary phase cells of B. cereus strains were subjected to TSB supplemented with NaClO (0-3.6%), H2O2 (0-0.28%) and acetic acid (0-1.5%) for 45-60 min, depending on the antimicrobials. Cell counts of B. cereus were enumerated on tryptic soy agar and the survival data of B. cereus were fitted to the simple linear regression to calculate death rates (log CFU/ml/min).
Results: Cell counts of all B. cereus strains decreased at 7 oC, but no differences (P > 0.05) of growth pattern were generally observed at 10-35 oC except for NaClO isolate (B. cereus S-BC-50 and S-BC-52) which had lower maximum cell density than other strains by 2 log CFU/ml at 10 oC. As B. cereus isolates were exposed to decontamination agents, exponential phase cells were more sensitive (P < 0.05) than those of stationary cells. Moreover, the differences in death rates (0.0-0.25 log CFU/ml/min) of isolates were not observed (P > 0.05) as subjected to the decontamination agents.
Significance: This result indicates that applications of decontamination agents may not cause different growth patterns and the resistance of B. cereus to the decontamination agents.