Applied and Environmental Microbiology, Mar. 1988, Vol.54, No.3, p. 741-747.
Departmenet of Environmental Healthl anid Department of Microbiology,
Received 30 March 1987/Accepted 21 December 1987

A study was conducted to determine the bactericidal effects of ozone and hydrogen peroxide relative to thatof free chlorine on Legionella pneumophila serogroup 1. In laboratory batch-type experiments, organisms seeded at various densities were exposed to different concentrations of these biocides in demand-free buffers. Bactericidal effects were measured by determining the ability of L. pneumophila to grow on buffered charcoal-yeast extract agar supplemented with a-ketoglutarate. Ozone was the most potent of the three biocides, with a greater than 99% kill of L. pneumophila occurring during a 5-min exposure to 0.10 to 0.30 ,ug of 03 per ml. The bactericidal action of 03 was not markedly affected by changes in pH or temperature. Concentrations of 0.30 and 0.40 ,ug of free chlorine per ml killed 99% of the L. pneumophila after 30- and 5-min
exposures, respectively. A 30-min exposure to 1,000 ,ug of H202 per ml was required to effect a 99% reduction of the viable L. pneumophila population. However, no viable L. pneumophila could be detected after a 24-h exposure to 100 or 300 ,ug of H202 per ml. Attempts were made to correlate the biocidal effects of 03 and H202 with the oxidation of L. pneumophila fatty acids. These tests indicated that certain biocidal concentrations of 03 and H202 resulted in a loss or severe reduction of L. pneumophila unsaturated fatty acids.
E.L.Domingue, R.L.Tyndall, W.R.Mayberry, O.C.Pancorbo