Enumeration and characterization of five pathogenic Legionella species from large research and educational buildings

Abstract

Legionella pneumophila is the species that is most often cultured from the natural environment, while disease-relevant Legionella species, such as Legionella micdadei, Legionella bozemanii, Legionella anisa, and Legionella longbeachae have yet to be extensively explored in premise plumbing systems. This study examined the concentrations of five pathogenic Legionella species (listed previously) in the influent and the taps of five different large buildings (BPS, ERC, F, FH, and M), undertaken during the start of two semesters (late summer/fall (August–September) and early winter/spring (January)). A total of 37 large-volume samples to examine building water quality (influents to the buildings and exposure sites (taps)) were collected and analyzed using droplet digital™ PCR. Legionella spp. (23S rRNA) were present in all water samples during both seasons. The majority (66%) of the exposure sites (bathroom taps) were positive for at least one target Legionella species (listed above). Results showed that pathogenic Legionella species were most often detected during the winter/spring sampling event – the percent positives for any one of the pathogenic Legionella species at the hot-water taps was 80% in building F and 40% in BPS, M, FH, and ERC. Legionella pneumophila and L. longbeachae were found in the highest concentrations (2.0 log₁₀ gene copies (GC)/100 mL) at the hot-water taps in buildings F and ERC, respectively. No strong relationships were found with the physical–chemical parameters. Overall, general Legionella spp. concentrations increased in the winter/spring samples due possibly to lower water usage (lower occupancy and no use of cooling towers, which led to more water stagnation or time in the system).