Effect Of Lactic Acid Stress On Biofilm Formation Of Escherichia Coli O26 At Different Temperatures

Similar to Escherichia coli O157, non-O157 also inherits certain acid resistance, and its stress response can be induced under acidic conditions, which may be affected by temperature. In this study, O26, the main serotype of non-O157 E. coli, was investigated in order to evaluate the effect of lactic acid stress on its biofilm formation (BF) at different temperatures. Firstly, the BF ability of 22 isolates of E. coli O26 were compared by means of crystal violet staining and the result showed that all strains had certain BF ability with variation among strains. Then, the strain 126Z with strong capacity and strain G13Z2 with medium capacity were selected for BF experiment in acidic TSB (pH 4.0 and 5.0, adjusted with lactic acid) at 15 degrees C and 25 degrees C, respectively. The results showed that the BF of O26 was decreased with increasing concentration of lactic acid, and the higher the concentration of lactic acid was, the less the amount of biofilm formed. Moreover, the effect of temperature on BF of different capacity strains was related to the pH value, that is, with a lower concentration of lactic acid, the higher the temperature was, the faster the biofilm amount increased. Under a higher acid concentration, the BF of two strains showed different dynamic changes and were inhibited in the later stage, in which the biofilm amount of 126Z decreased significantly at 15 degrees C, while that of G13Z2 decreased more significant at 25 degrees C. This observation was further confirmed by scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM). This finding suggests that combined temperature and lactic acid intervention may be an effective method to prevent BF, and the results of present work would provide scientific basis for the risk assessment of E. coli O26 in food processing.