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Updated: Dec 27, 2025
Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes
Published on: March 3, 2023
Antimicrobial Susceptibility Patterns of Legionella spp. Strains Isolated from Water Systems in Morocco
Abdelwahid Assaidi1,2, Mostafa Ellouali1, Hassan Latrache1
1Laboratory of Bioprocess and Biointerfaces, Life Sciences Department, Faculty of Sciences and Techniques, Sultan Moulay Slimane University, Beni Mellal, Morocco.
Abstract:
Legionella is a waterborne pathogen that causes a severe form of pneumonia called Legionnaires' diseases, which is normally acquired by inhalation of aerosols containing Legionella originating from natural and man-made water systems. The aim of this study was to describe the level of antimicrobial susceptibility of environmental Legionella spp. strains to preferred and recommended therapeutic agents to treat Legionella disease. The minimum inhibitory concentrations (MICs) of 60 environmental Legionella spp. strains were tested using the broth dilution method. Susceptibility testing was performed for 12 antimicrobial agents: macrolides (erythromycin, azithromycin [AZI], and clarithromycin [CLA]), fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin, and gemifloxacin), a ketolide (telithromycin), cefotaxime (CEF), tigecycline (TIG), doxycycline (DOX), and rifampicin (RIF). All tested strains of Legionella spp. were inhibited by low concentrations of fluoroquinolones and macrolides. Regarding the macrolides, CLA was the most active antibiotic, and AZI was the least active. RIF was the most effective antibiotic against the isolates in vitro. All isolates were inhibited by the following antibiotics (in decreasing order of their MICs): DOX>CEF>TIG. No resistance against these drugs was detected, and all isolates were inhibited by low concentrations of the tested antibiotics. Susceptibility testing of environmental Legionella spp. isolates must be monitored often to detect and evaluate the possible development of antibiotic resistance.
Insights
Environmental Legionella bacteria are susceptible to common antibiotics like macrolides and fluoroquinolones. Ongoing monitoring is crucial to detect potential antibiotic resistance in Legionella strains.
Area of Science:
- Environmental microbiology
- Infectious diseases
- Antimicrobial resistance
Background:
- Legionella is a waterborne pathogen causing severe pneumonia (Legionnaires' disease).
- Infection occurs via inhalation of contaminated aerosols from water systems.
- Understanding antimicrobial susceptibility is key for effective treatment.
Purpose of the Study:
- To determine the antimicrobial susceptibility of environmental Legionella spp. strains.
- To evaluate efficacy of preferred and recommended therapeutic agents.
- To inform treatment strategies for Legionella disease.
Main Methods:
- Tested 60 environmental Legionella spp. strains.
- Used broth dilution method to determine Minimum Inhibitory Concentrations (MICs).
- Evaluated 12 antimicrobial agents including macrolides, fluoroquinolones, and others.
Main Results:
- All strains were susceptible to low concentrations of fluoroquinolones and macrolides.
- Clarithromycin was the most active macrolide; azithromycin was least active.
- Rifampicin showed the highest in vitro efficacy; no resistance was detected.
Conclusions:
- Environmental Legionella isolates are highly susceptible to tested antibiotics.
- Continuous monitoring for antibiotic resistance is essential.
- Current therapeutic agents remain effective against environmental strains.
