夾雑菌存在下におけるmodified EC培地での下痢原性大腸菌の増殖が抑制される要因

抄録

This study aimed to determine the cause of growth inhibition of diarrheagenic Escherichia coli (DEC) in modified EC (mEC) broth containing other bacteria. The growth of DEC in mEC broth with non-DEC bacteria was evaluated by lactose fermentation, growth rate, and the ratio of DEC to non-DEC bacteria before enrichment culturing. The results showed that non-lactose fermenting bacteria did not compete with DEC because lactose contributes considerably to the growth of bacteria in mEC broth. In the mEC broth, all the bacteria stopped growing after the total number of bacteria reached approximately 9.0 log CFU/mL, primarily because of lactose depletion. Moreover, the growth of DEC in mEC broth with coliform bacteria depends on the ratio of DEC to coliform bacteria in the specimen and the growth rate of coliform bacteria. However, DEC isolation cannot exclude the influence of non-pathogenic E. coli in the specimen because most DEC possess drug susceptibility and biochemical characteristics similar to non-pathogenic E. coli. Estimation of the DEC population in mEC broth after enrichment culturing by quantitative PCR is useful to predict the result of DEC isolation. Moreover, the use of isolation media other than those identified by lactose fermentation can improve the detection rate of DEC.