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 chemos tat culture under aerobic, oxygen-limited and anaerobic conditions. The gro wth and metabolic efficiency of oxygen-limited and anaerobic cultures was i mpaired, with biomass yield and the molar growth yield for glucose, Y-gluco se, reduced markedly in comparison with aerobic cultures. Steady state cell s 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 a dhesive for HEp-2 monolayers than cells grown in aerobic batch culture. Fur thermore, oxygen-limited and anaerobic cultures were significantly more adh esive for Hep-2 cells when compared with cells grown in aerobic chemostat c ulture, possibly reflecting increased pathogenicity associated with the ind uction of novel adhesins. Type 1 pill were not responsible for increased ad herence. Verocytotoxins, VT1 and VT2, were expressed constitutively and wer e not influenced by oxygen availability. This study demonstrates that E. ro ll O157 is a versatile micro-organism, which responds to environmental cond itions likely to be encountered during infection by inducing a phenotype wh ich is more adhesive for human epithelial cells.