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 hydrophil a isolated from a hospital water facility and patients with nosocomial infe ctions in a French medical school hospital. In-vitro bactericidal activity was determined by a macro- and micromethod, using specific interfering subs tances over a range of dilutions and temperatures, after 1 and 5 minute exp osure times. A 10(5)-fold reduction in the challenge inoculum was taken as the criterion of efficacy. Results obtained by both methods agreed and indi cated a median minimal bacterial concentration of chlorine of from 0.95 ppm without interfering substances to 297 ppm in the presence of interfering s ubstances. These data indicate that Aeromonas hydrophila isolates are relat ively resistant to chlorine, thus precluding the use of chlorine alone as a disinfectant for water supplies contaminated with Aeromonas spp.