The response of the standard Escherichia coli K-12 and enteroinvasive Escherichia coli to an acidic environment

Pre-exposure of log phase enteric bacteria, to non-lethal acidic pH induces phenotypic changes that protect the organisms against subsequent, lethal acidity. It is presumed that in Escherichia coli (E. coli ) the induced, stress response throughout the pH range of 4.2 to 5.8 is the same, although research has shown that there are two different responses at pH 5.0 and 4.3 in Salmonella typhimurium ( S. typhimurium). This research sought to determine whether the latter finding might apply to E. coli, and whether pre-exposure to acid plays a role in either the pathogenicity or virulence of E. coli strains. Experiments included pH 3.0 acid survival assays of log phase E. coli K-12, MG 1655, and enteroinvasive strains EIEC 10012 and 10016, after they had been exposed to media acidified to pH 5.5 and or pH 4.3, and comparison of their polypeptide profiles. The pH 5.5-exposed and unexposed cultures were also tested, and compared for both invasion capabilities, and the extent of intracellular multiplication in HEp-2 cells. Extracts containing radiolabeled polypeptides from EIEC 10012 grown intracellularly in both HEp-2 and CaCo-2 cells were examined by two-dimensional gel analysis, and the profiles compared to those produced earlier after exposure to acified media. The results indicate that like S. typhimurium, E. coli shows both an acid tolerance and acid shock response to pH 5.5 and 4.3 exposure respectively. However, unlike S. typhimurium, extension of the period of preexposure resulted in better protection. Additionally, a paradox exists because pH 4.3 induced a weaker polypeptide response, but a more decisive acid protection Acid exposure improved the invasion of both EIEC strains, but only the multiplication of EIEC 10016. The induced protein pattern resulting from the stress of an intracellular environment was not the same as that resulting from exposure to acidified medium, despite the exposure of intracellular cells to acidic phagocytic vesicles. Heat shock proteins were predominant after intracellular growth, while several low molecular weight polypeptides appeared after inorganic acid exposure. The low molecular weight polypeptides warrant further investigation because some might be necessary for the observed acid protection. This is the first report of alternate polypeptide profile induced in EIEC intracellularly or extracellularly.