Purpose: Therefore, the objective of this study to compare the heat resistance and biofilm formation among Escherichia coli serotypes.
Methods: E. coli O157:H7 NCCP11142, E. coli O111 ATCC12795, and E. coli O26 ATCC43887 exposed to 0, 2, and 4% NaCl supplemented in tryptic soy broth (TSB), and E. coli cells were harvested at early stationary and late stationary phases. The E. coli cells were washed twice with phosphate buffer solution. Inocula of E. coli O157:H7, E. coli O111, and E. coli O26 were inoculated into TSB plus 0, 2, and 4% NaCl, followed by exposure to 50°C for 2 h. The survivals of E. coli serotypes were then enumerated on tryptic soy agar. In addition, the NaCl-exposed cells were inoculated into 96-well microtiter plate, followed by incubation at 35°C for 24 h. Biofilms were then measured by crystal violet.
Results: E. coli O157:H7 exposed to 4% NaCl had higher (P < 0.05) heat resistance than other E. coli serotypes, regardless of growth stage. Comparing biofilm formation, biofilms of three E. coli serotypes generally decreased (P < 0.05) for early and late stationary stage cells, except for the early stationary stage cells of E. coli O26. In addition, late stationary cells formed more biofilms (P < 0.05) than early stationary cells.
Significance: This result indicates that different serotypes of E. coli have different stress responses and biofilm formation.