Untersuchungen zum Wachstum und zur Persistenz von Escherichia coli O26:H11, O157:H7, O157:H45 und O159:H- bei Säurestress

Shiga toxin-producing Escherichia (E.) coli (STEC) are a major cause of foodborne diseases in humans. STEC infections have also been associated with acidified or fermented products. This fact may indicate an increased acid resistance of STEC. In the present study, four pathogenic E. coli strains (STEC 0157:H7, STEC O26:H11, STEC O159:H - , EPEC 0157:H45) and a control strain (E coli K12) were examined for growth and persistence under hydrochloric, acetic and lactic acid stress. In the growth experiments, the 0157:H45 strain (hydrochloric and acetic acid) and the 0157:H7 strain (acetic acid) showed improved acid resistance, whereas no differences were evident for the other strains. In the survival experiments, significant differences were found between strains in the stationary and logarithmic growth phase. By comparison of the three acids, acetic acid proved to be most effective for growth inhibition and inactivation. The comparison of acid adapted and non adapted STEC O157:H7, STEC O159:H - and E coli K12 showed that strains adapted with hydrochloric acid exhibited improved acid resistance, but this effect was not confirmed after lactic acid adaptation. The adaptation with acetic acid improved the acid resistance of STEC O159:H - and E. coli K12, whereas that of STEC 0157:H7 was not affected. Consequently, remarkable strain-to-strain variation in the acid stress response of "enteropathogenic" E. coli was evident. This variation was rather influenced by the acid applied than by the serotype or the pattern of virulence factors of the strains.