Factors Affecting the Dynamics of Legionella pneumophila, Nontuberculous Mycobacteria, and Their Host Vermamoeba vermiformis in Premise Plumbing

Premise plumbing are complex systems with diverse materials and variable temperature and stagnation time. Opportunistic pathogens are commonly found in premise plumbing, but little is known about the impact of design and operational characteristics of building water systems on their occurrence and survival in water and biofilms. The main objective of this study was to investigate the interplay between material type, temperature, and stagnation on the occurrence and survival of Legionella pneumophila, nontuberculous mycobacteria (NTM), and their host Vermamoeba vermiformis. Twelve CDC biofilm reactors were used to compare concentrations of these microorganisms measured by qPCR in water and biofilms, at 25, 40, 55, or 60 C-degrees, and in contact with six materials: polypropylene (PP), polyvinyl chloride (PVC), EPDM, cross-linked polyethylene (PEX), stainless steel (SS), and copper (Cu). The addition of V. vermiformis induced an average 1.4-log increase in NTM concentrations, while the spiking of two L. pneumophila strains caused a 3-log decrease in NTM in PP and PEX biofilms. Heating at 55 and 60 C-degrees in copper reactors led to the decline in V. vermiformis and L. pneumophila below the qPCR quantification limit. A rebound of culturable L. pneumophila was noted after a 6 month stagnation period at room temperature in water with PVC and stainless steel coupons.