An in-vitro evaluation of the activity of chlorine against environmental and nosocomial isolates of Aeromonas hydrophila

A chlorine preparation was tested against 34 strains of Aeromonas hydrophila isolated from a hospital water facility and patients with nosocomial infections in a French medical school hospital. In-vitro bactericidal activity was determined by a macro- and micromethod, using specific interfering substances over a range of dilutions and temperatures, after 1 and 5 minute exposure times. A 10(5)-fold reduction in the challenge inoculum was taken as the criterion of efficacy. Results obtained by both methods agreed and indicated a median minimal bacterial concentration of chlorine of from 0.95 ppm without interfering substances to 297 ppm in the presence of interfering substances. These data indicate that Aeromonas hydrophila isolates are relatively resistant to chlorine, thus precluding the use of chlorine alone as a disinfectant for water supplies contaminated with Aeromonas spp.