*4.2. Culture Media*

To distinguish between *Legionella* spp. and non-*Legionella* bacteria, two di fferent media were used: 0.1% BCYE α agar and BCYE α agar supplemented with 3 g/<sup>L</sup> glycine, 50,000 IU of polymyxin B, 0.001 g/<sup>L</sup> of vancomycin, 0.08 g/<sup>L</sup> of anisomycin, 0.01 g/<sup>L</sup> of bromothymol blue, and 0.01 g/<sup>L</sup> of bromocresol purple (MWY). The formulations of both media conform to ISO 11731 [10].

Commercially available agar plates were purchased by Oxoid Ltd. (Basingstoke, UK) or Xebios Diagnostics GmbH (Düsseldorf, Germany). For each batch supplied, each manufacturer provided us with detailed quality control information (e.g., type of bacteria, pH, colony morphology, selectivity, recovery and expected results). The microbiological performance test was carried out in accordance with ISO 11133:2014 requirements [20]: for BCYE α agar, colony count of positive strains was ≥70% for each inoculum (i.e., productivity); for MWY agar, colony count of positive strains was ≥50% for each inoculum (i.e., selectivity).
