First description of blaCTX-M-1-carrying Escherichia coli isolates in Danish primary food production.

was prevented completely by DW-224a at concentrations of 1·, 2· and 4· MIC by 24 h, although regrowth occurred in the presence of ciprofloxacin at 1· MIC concentration. DW-224a also showed a dose-dependent bactericidal activity against all test organisms up to 4· the MIC. The MBCs of DW-224a in Mueller–Hinton broth (MHB) were identical to 1·MIC or at most twice the MIC for all strains tested. Because the bactericidal activities of DW-224a increased with increasing concentrations (up to a concentration of 2 mg/L) for all test strains, and because the slope of the lines (rate of activity) in the time–kill curve varied with concentration, we concluded that DW-224a had concentration-dependent bactericidal activities regardless of the tested strains. Mutations within QRDR of the genes encoding DNA gyrase in S. pneumoniae strains did not affect the bactericidal activities of DW-224a, ciprofloxacin and gemifloxacin. PAE of DW-224a was determined using a broth technique in MHB. The PAE was calculated by the following equation: PAE = T – C, where T is the time to achieve 1 log10 cfu/mL growth for the antibiotic-exposed sample and C is the time to achieve 1 log10 cfu/mL growth for the untreated control sample (Table 1). In summary, DW-224a showed very potent and dosedependent bactericidal effect against all strains tested. The clinical usefulness of DW-224a should be established by further studies.