**Sensitivity and Selectivity of Two Commercially Available Media for** *Legionella* **spp. Recovery from Environmental Water Samples**

#### **Savina Ditommaso \*, Monica Giacomuzzi, Gabriele Memoli, Jacopo Garlasco and Carla M. Zotti**

Department of Public Health and Pediatrics, University of Turin, 10126 Turin, Italy; monica.giacomuzzi@unito.it (M.G.); gabriele.memoli@unito.it (G.M.); jacopo.garlasco@unito.it (J.G.); carla.zotti@unito.it (C.M.Z.)

**\*** Correspondence: savina.ditommaso@unito.it; Tel.: +39-0116705841; Fax: +39-0116705881

Received: 11 May 2020; Accepted: 22 June 2020; Published: 29 June 2020

**Abstract:** The quality control of culture media used for *Legionella* spp. isolation and enumeration is paramount to achieve a satisfactory degree of comparability among water testing results from different laboratories. Here, we report on a comparative assessment of the sensitivity and selectivity of MWY and BCYEα media supplied by two different manufacturers (i.e., Xebios Diagnostics GmbH and Oxoid Ltd) for the detection of *Legionella* spp. from environmental water samples. Even though our analysis showed an excellent agreemen<sup>t</sup> between the recovery rates of the four media tested (90.5%), the quantitative recovery of *Legionella* spp. colonies using Xebios media was significantly greater than that achieved by Oxoid media (*P* = 0.0054). Furthermore, the sensitivity of detection was significantly higher when samples were plated on MWY Xebios agar (*P* = 0.0442), while the selectivity of MWY appeared to be the same regardless of the manufacturer. Furthermore, MWYXebios agar favored the growth of much larger colonies compared to those observed on MWYOxoid agar. Finally, MWYXebios medium enhanced the recovery of non-*pneumophila Legionella* species. Collectively, our findings demonstrate that quality control is crucial to ensure high selectivity and sensitivity of the culture media used for the detection and enumeration of *Legionella* spp. from environmental water resources. As water remediation measures strictly depend on *Legionella* spp. recovery, culture protocol standardization, as well as quality control of the culture media, is essential to achieve intra- and interlaboratory reproducibility and accuracy.

**Keywords:** *Legionella* spp.; culture media; environmental monitoring; quality control
