*Legionella* **Diversity and Spatiotemporal Variation in the Occurrence of Opportunistic Pathogens within a Large Building Water System**

#### **Helen Y. Buse 1,\*, Brian J. Morris 2, Vicente Gomez-Alvarez 3, Je**ff**rey G. Szabo 1 and John S. Hall 1**


Received: 8 June 2020; Accepted: 7 July 2020; Published: 13 July 2020

**Abstract:** Understanding *Legionella* survival mechanisms within building water systems (BWSs) is challenging due to varying engineering, operational, and water quality characteristics unique to each system. This study aimed to evaluate *Legionella*, mycobacteria, and free-living amoebae occurrence within a BWS over 18–28 months at six locations differing in plumbing material and potable water age, quality, and usage. A total of 114 bulk water and 57 biofilm samples were analyzed. *Legionella* culturability fluctuated seasonally with most culture-positive samples being collected during the winter compared to the spring, summer, and fall months. Positive and negative correlations between *Legionella* and *L. pneumophila* occurrence and other physiochemical and microbial water quality parameters varied between location and sample types. Whole genome sequencing of 19 presumptive *Legionella* isolates, from four locations across three time points, identified nine isolates as *L. pneumophila* serogroup (sg) 1 sequence-type (ST) 1; three as *L. pneumophila* sg5 ST1950 and ST2037; six as *L. feeleii*; and one as *Ochrobactrum*. Results showed the presence of a diverse *Legionella* population with consistent and sporadic occurrence at four and two locations, respectively. Viewed collectively with similar studies, this information will enable a better understanding of the engineering, operational, and water quality parameters supporting *Legionella* growth within BWSs.

**Keywords:** potable water; first draw; second draw; biofilm; whole genome sequencing; environmental monitoring; premise plumbing systems
