The Minimal “Chlorine Death Points” of Bacteria

Abstract

Minimal "chlorine death points" required to kill in 15-30 sec., were determined for 503 strains of 48 bacterial spp. Intestinal and respiratory vegetative pathogens were killed by 0.15-0.25 p.p.m. in 15-30 sec; B. coli was somewhat more resistant. Spore-bearers were 10-1,100 times more resistant than vegetative cells. Cl death points of spores ranged from 2.5 p.p.m. for Cl. welchii to 280 p.p.m. for B. vulgatus. B. subtilis at 160 p.p.m. was considered best adapted and safest as an index organism of the spore-bearer group. The primary purpose of chlorination is to safeguard against a relatively few intestinal and respiratory vegetative pathogens. Regular and consistent destruction of B. coli appears to be a more suitable practical criterion of effective Cl disinfection than the total bacterial count or B. subtilis.