DETECTION OF LEGIONELLA pneumophila IN AQUATIC ENVIRONMENTS AND ITS CONTROL BY CHLORINATION IN COOLING TOWER SYSTEMS

Abstract

Legionnaires' disease is a severe pneumonia caused by the gram negative, bacterium L. pneumophila which is widespread in aquatic environments. Use of a modified DGVP base medium and the direct fluorescent antibody (DFA) method proved to be valuable for identification and enumeration of L. pneumophila populations present in aquatic environments sampled for this study. An initial survey conducted in July 1988, within Frederick County, Maryland, showed the presence of L. pneumophila populations in various aquatic environments including lakes, ponds, streams, and cooling tower water systems. Cooling tower water systems at the Frederick Cancer Research Facility, were shown to contain populations of L. pneumophila ranging from 1.0 x 10⁵ to 5.5 x 10⁶ CFU (colony forming units) per ml. The presence of Chlorella (green alga) and Oscillatoria (cyanobacterium) in the cooling tower water systems agree with reports that L. pneumophila is frequently associated with algae and cyanobacteria in aquatic environments. Chlorine treatment (October 1988) of the cooling tower water systems containing L. pneumophila demonstrated that chlorine levels greater than 20 ppm resulted in a total reduction of L. pneumophila populations. A laboratory experiment conducted to measure the effect of various concentrations of chlorine on known amounts of L. pneumophila populations agreed with results of the chlorine treatments conducted on the cooling tower systems.