Chlorine disinfection of Francisella tularensis.

Aims:  To determine the range of free available chlorine (FAC) required for disinfection of the live vaccine strain (LVS) and wild-type strains of Francisella tularensis. Methods and Results:  Seven strains of planktonic F. tularensis were exposed to 0·5 mg·l−1 FAC for two pH values, 7 and 8, at 5 and 25°C. LVS was inactivated 2 to 4 times more quickly than any of the wild-type F. tularensis strains at pH 8 and 5°C. Conclusions:  Free available chlorine residual concentrations routinely maintained in drinking water distribution systems would require up to two hours to reduce all F. tularensis strains by 4 log10. LVS was inactivated most quickly of the tested strains. Significance and Impact of the Study:  This work provides contact time (CT) values that are useful for drinking water risk assessment and also suggests that LVS may not be a good surrogate in disinfection studies.