Abstract
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.
Highlights
Legionella pneumophila has been found worldwide to be a relatively common pulmonary pathogen of severe community-acquired or nosocomial pneumonia[1,2,3]
The susceptibilities of 93 environmental and 12 clinical L. pneumophila strains to 10 antimicrobial agents commonly used in legionellosis therapy were analyzed
The minimal inhibitory concentration (MIC) obtained for both S. aureus and E. coli were generally lower but within an order of magnitude compared to the findings of previous studies[33,34]
Summary
Legionella pneumophila has been found worldwide to be a relatively common pulmonary pathogen of severe community-acquired or nosocomial pneumonia[1,2,3]. 25 of the 59 described Legionella species have been implicated in human disease[11,12,13], the vast majority of cases are caused by L. pneumophila strains, most of which belong to serogroup 114–16 Isolates of this common serogroup should be genotyped and further differentiated in order to evaluate the efficacy of antimicrobial agents in their treatment. Rodríguez-Martínez et al.[22] and Sharaby et al.[23,24] showed that the level of genotypes (analyzed by MLVA-8) should be addressed in order to get insights into ecological traits of L. pneumophila strains inhabiting drinking water distribution systems (DWDSs). Analysis of the three dominant genotypes showed that they could be addressed as different ecotypes with a distinct temperature range, growth kinetics, virulence and abundances at their site of dominance[22,23,24]
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