Resistance of biofilm formation and formed-biofilm of Escherichia coli O157:H7 exposed to acid stress

O157 is the most common serogroup of Enterohemorrhagic Escherichia coli responsible for the most outbreaks, partly due to its acid tolerance. Biofilm formation of H. coli O157:417 and its response to lactic acid stress were determined in this study. Results showed that the biofilm formation of 11 isolates greatly depended on the strain; specifically, the 329 isolate showed strong capacity. As compared to CICC 21530 isolate exhibiting weak capacity of biofilm formation on polystyrene microplates, a classic dynamic of biofilm formation was observed for J29. The growth of biofilm and planktonic cells of selected strains (J29 and CICC 21530) varied after exposure to pH 4.0, 4.5, 5.0, and 7.2 (control). A similar survival and growth profiles of planktonic cells response to stress was found between J29 and CICC 21530, whereas J29 showed high resistance to acid stress during biofilm formation, which was further confirmed using SEM. Moreover, the formed-biofilm of J29 showed more resistance to pH 2.0 and 3.5, with more than 4 log CFU/cm(2) cells remaining after 12 h treatment, whereas less than 3 log CFU/cm(2) cells survived for CICC 21530. The finding suggested that a combination of interventions might be an effective intervention for eliminating the biofilm.