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Published on: March 3, 2023
Antibiotic susceptibility pattern of Portuguese environmental Legionella isolates
Carolina Cruz1, Lúcia Rodrigues2, Filipa Fernandes3
1NOVA Medical School, Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisboa, Portugal.
Introduction:
Legionnaires' Disease is a pneumonia caused by Legionella spp., currently treated empirically with fluoroquinolones and macrolides. In this study, we aim to describe the antibiotic susceptibility pattern of environmental Legionella recovered in the south of Portugal.
Methods:
Minimal inhibitory concentration (MIC) determination of 57 Legionella isolates (10 Lp sg 1, 32, Lp sg 2-14 15 L. spp) was achieved by broth microdilution, as described by EUCAST, for azithromycin, clarithromycin, ciprofloxacin, levofloxacin, and doxycycline.
Results:
Fluoroquinolones were the most active antibiotic, displaying the lowest MIC values in contrast to doxycycline which had the highest. MIC90 and epidemiological cut-off (ECOFF) values were, respectively, 0.5/1 mg/L for azithromycin, 0.125/0.25 mg/L for clarithromycin, 0.064/0.125 mg/L for ciprofloxacin, 0.125/0.125 mg/L for levofloxacin and 16/32 mg/L for doxycycline.
Discussion:
MIC distributions were higher than reported by EUCAST for all antibiotics. Interestingly, two phenotypically resistant isolates with high-level quinolone resistance were identified. This is the first time that MIC distributions, lpeAB and tet56 genes have been investigated in Portuguese environmental isolates of Legionella.
Insights
This study analyzed the antibiotic susceptibility of environmental Legionella in Portugal. Fluoroquinolones showed the highest activity, though some isolates exhibited high-level quinolone resistance.
Area of Science:
- Environmental microbiology
- Antimicrobial resistance
- Infectious diseases
Background:
- Legionnaires' disease is a severe pneumonia caused by Legionella bacteria.
- Current empirical treatments include fluoroquinolones and macrolides.
- Understanding local antibiotic susceptibility is crucial for effective treatment.
Purpose of the Study:
- To determine the antibiotic susceptibility patterns of environmental Legionella isolates in southern Portugal.
- To investigate the prevalence of specific resistance genes in these isolates.
Main Methods:
- Collected 57 environmental Legionella isolates from southern Portugal.
- Determined Minimal Inhibitory Concentrations (MICs) using broth microdilution according to EUCAST guidelines.
- Tested susceptibility to azithromycin, clarithromycin, ciprofloxacin, levofloxacin, and doxycycline.
Main Results:
- Fluoroquinolones (ciprofloxacin, levofloxacin) demonstrated the lowest MIC values, indicating high activity.
- Doxycycline exhibited the highest MIC values.
- MIC distributions exceeded EUCAST-reported values for all tested antibiotics.
- Two isolates displayed phenotypical resistance with high-level quinolone resistance.
Conclusions:
- Environmental Legionella in southern Portugal show varying susceptibility patterns.
- The emergence of high-level quinolone resistance is a significant concern.
- This study provides the first investigation of MIC distributions and specific resistance genes (lpeAB, tet56) in Portuguese environmental Legionella.
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