Antimicrobial susceptibility test of Legionella pneumophila human strains isolated in Italy (1987-2020): correlation with epidemiological and molecular data

Antimicrobial treatment of Legionnaires disease is a fairly established practice and infections due to Legionella pneumophila (Lp) antimicrobial resistance strains are not yet an emergence. However, in recent years, Lp strains with increased resistance to azithromycin have been documented. Aim of this study was to investigate the antimicrobial susceptibility of Lp human strains isolated in Italy. 202 Lp strains isolated in Italy from 1987 to 2018 were tested for sensitivity to the 9 antibiotics as suggested by EUCAST Legionella guidance document, but using micro-dilution assays in BCYE broth. The strains were typed for their Sequence Type (ST) by sequence based (SBT) and Lp1 for their monoclonal subgroup by monoclonal antibodies (MAb). Minimum Inhibitory Concentrations (MICs) data were correlated with possible exposure (community, nosocomial or travel associated) and geographical distribution. The presence of the efflux pump gene LpeAB in the azithromycin resistance strains was also investigated.