Legionella pneumophila causes human lung
infections resulting in severe
pneumonia. High-resolution genotyping of L. pneumophila isolates can be achieved by multiple-locus variable-number tandem-repeat analysis (MLVA-8). Legionella
infections in humans occur as a result of inhalation of bacteria-containing
aerosols, thus, our aim was to study the antimicrobial susceptibilities of different MLVA-8 genotypes to ten commonly used
antimicrobial agents in
legionellosis therapy. Epidemiological cut-off values were determined for all
antibiotics. Significant differences were found between the
antimicrobial agents' susceptibilities of the three studied environmental genotypes (Gt4, Gt6, and Gt15). Each genotype exhibited a significantly different susceptibility profile, with Gt4 strains (Sequence Type 1) significantly more resistant towards most studied
antimicrobial agents. In contrast, Gt6 strains (also Sequence Type 1) were more susceptible to six of the ten studied
antimicrobial agents compared to the other genotypes. Our findings show that environmental strains isolated from adjacent points of the same water system, exhibit distinct antimicrobial resistance profiles. These differences highlight the importance of susceptibility testing of Legionella strains. In Israel, the most extensively used
macrolide for
pneumonia is
azithromycin. Our results point at the fact that
clarithromycin (another
macrolide) and
trimethoprim with
sulfamethoxazole (SXT) were the most effective
antimicrobial agents towards L. pneumophila strains. Moreover,
legionellosis can be caused by multiple L. pneumophila genotypes, thus, the treatment approach should be the use of combined
antibiotic therapy. Further studies are needed to evaluate specific antimicrobial combinations for
legionellosis therapy.