type="media"} and in the Methods section 2.3.

Determination of MICs {#Sec6}
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Isolates from buffered charcoal yeast extract agar supplemented with α-ketoglutarate (BCYE-α) plates (BD Diagnostics Sparks, MD) were suspended in 0.85% NaCl solution to a 0.5 McFarland standard and subjected to MIC test strip (Liofilchem s.r.l., Italy) on BCYE-α plates. A sterile cotton swab was soaked in the inoculum suspension of each isolate. Each swab was then streaked over the entire BCYE-α agar plate surface. Plates were left to dry for 10 minutes so that the surface was completely dry before applying the Epsilometer test gradient strip. The following antimicrobial agents were used: Azithromycin, Clarithromycin, Ciprofloxacin, Moxifloxacin, Rifampicin, Tigecycline, Doxycycline, Levofloxacin, Erythromycin, and Trimethoprim-sulfamethoxazole. The MICs were read after 48 hours of incubation at 35 ± 1 °C at 2.5% CO~2~. The MIC of each antimicrobial agent was taken as the lowest concentration of the antimicrobial agent at which the zone of inhibition intersected the strip. MIC tests for *L. pneumophila* isolates were repeated in triplicates. Epidemiological Cut-off values (ECOFFs) were determined according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines for *Legionella pneumophila*^[@CR31]^. Briefly, MIC values were fitted to the cumulative log-normal distribution using non-linear least squares regression in order to determine the ECOFF for each antimicrobial agent^[@CR31]^.

Statistical analysis {#Sec7}
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All statistical analyses were performed using IBM SPSS 22® and Primer7 software (Primer-e, Auckland, New Zealand). All tests were applied at a 95% level of confidence. Repeated-measures analysis of variance (ANOVA) was applied to study the differences between the MICs of different antimicrobials. Data sphericity was not violated (Mauchly's test: *p* \> 0.05). T-tests were applied in order to compare the antimicrobials' MICs for strain