Legionella pneumophila occurrence in waters of east central Indiana

Drinking water is a potential means of transmission for the opportunistic bacterial pathogen Legionella pneumophila. This study evaluated the presence of Legionella pneumophila in source water supplies, granular activated carbon (GAC) filtered water, and the network of a public drinking water system in east central Indiana using a pilot three-tiered approach. Water samples were enriched for Legionella spp. by cultivation on selective media, followed by direct fluorescent antibody (DFA) staining for L. pneumophila serogroups 1-14, and duplex real-time polymerase chain reaction (PCR). PCR targets included a 16S rDNA segment and a macrophage infectivity potentiator (mip) gene fragment of L. pneumophila. Sensitivity of culture methods and PCR was determined by percent recovery and by using serial dilutions of L. pneumophila DNA, respectively. Sensitivity of the real-time PCR assay was 230 genome equivalents (GE) of L. pneumophila per liter of GAC filtered or distribution waters, and 230 GE per 100 ml source water. All source water samples were positive for L. pneumophila by DFA versus 80% by real-time PCR. Forty percent of GAC water samples were positive by DFA versus 20% by real-time PCR. Potable water samples yielded the lowest percentage with 12.5% positive for both DFA and real-time PCR.