[Bactericidal effect of chlorine on strains of Legionella species]

We have previously reported that the hot water of 17 (42.5%) out of 40 thermal baths were contaminated with legionellae. Our recent investigation revealed that legionellae inhabited 39 (66.1%) of the 59 thermal bath water, and their viable counts were at the level of 10(4) CFU/100 ml in 5 baths and 10(5) CFU/100 ml in another 5. Accordingly, the bactericidal effects of free chlorine on 102 strains of 22 Legionella species were tested, in order to find a method of controlling legionellae in thermal bath water. The test strains were the type strains of 22 species, 35 strains of 4 species from patients with Legionella pneumonia in Japan, and 45 strains of 4 species from thermal bath water. Viable cells of all 102 strains suspended at the concentration of 10(5) CFU/100 ml in sodium hypochloride solution with 0.4 mg/l free chlorine became undetectable within 15 min.