Influence of oxygen availability on physiology, verocytotoxin expression and adherence of Escherichia coli O157

A Strain of Escherichia coli serotype O157 was grown in steady state chemostat culture under aerobic, oxygen-limited and anaerobic conditions. The growth and metabolic efficiency of oxygen-limited and anaerobic cultures was impaired, with biomass yield and the molar growth yield for glucose, Y-glucose, reduced markedly in comparison with aerobic cultures. Steady state cells were typically short rods 2-3 mu m long, and were encapsulated by a layer of extracellular material. The majority of cells were non-flagellated and fimbriae were not observed. Chemostat-grown cells were significantly more adhesive for HEp-2 monolayers than cells grown in aerobic batch culture. Furthermore, oxygen-limited and anaerobic cultures were significantly more adhesive for Hep-2 cells when compared with cells grown in aerobic chemostat culture, possibly reflecting increased pathogenicity associated with the induction of novel adhesins. Type 1 pill were not responsible for increased adherence. Verocytotoxins, VT1 and VT2, were expressed constitutively and were not influenced by oxygen availability. This study demonstrates that E. roll O157 is a versatile micro-organism, which responds to environmental conditions likely to be encountered during infection by inducing a phenotype which is more adhesive for human epithelial cells.