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Antimicrobial susceptibility testing of Finnish Bordetella pertussis isolates collected during 2006-2017
Emilia Lönnqvist1, Alex-Mikael Barkoff1, Jussi Mertsola2
1Institute of Biomedicine, Research Center for Cancer, Infections and Immunity, University of Turku, Turku, Finland.
Objectives:
Macrolides, such as azithromycin and erythromycin, are first-line drugs for the (prophylactic) treatment of pertussis. This study aimed to screen for macrolide-, quinolone- or trimethoprim/sulfamethoxazole (SXT)-resistant strains among Finnish Bordetella pertussis isolates.
Methods:
Antimicrobial susceptibility testing was performed on 148 B. pertussis strains isolated during 2006-2017. Isolates were analysed by allele-specific PCR for detection of the macrolide resistance-associated mutation A2047G in the 23S rRNA gene. The gyrA gene was sequenced for detection of the A260G mutation associated with quinolone resistance. For phenotyping, a random selection was made by selecting every third isolate (n=50) to determine the minimum inhibitory concentrations (MICs) for erythromycin and azithromycin by Etest and the inhibition zone size for nalidixic acid (NAL) and SXT by single disk diffusion assay.
Results:
Neither the macrolide resistance-associated mutation A2047G nor the quinolone resistance-associated mutation A260G was detected in any of the B. pertussis isolates. MICs of azithromycin and erythromycin ranged between 0.016-0.19μg/mL and 0.016-0.25μg/mL, respectively. The size of the inhibition zone surrounding the NAL disk ranged between 22-27mm in diameter. The inhibition zone surrounding the SXT disk ranged between 24-37mm in diameter. No isolates resistant to any of the tested antimicrobials were identified.
Conclusions:
The allele-specific PCR is a simple and useful tool for screening B. pertussis resistance to macrolides. All Finnish isolates tested were susceptible to macrolides, quinolones and SXT.
Insights
No resistant Bordetella pertussis strains were found in Finland. All tested Finnish isolates remained susceptible to macrolides, quinolones, and trimethoprim/sulfamethoxazole (SXT), indicating no emerging antimicrobial resistance.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Pertussis, or whooping cough, is a highly contagious respiratory infection.
- Macrolides like azithromycin and erythromycin are primary treatments for pertussis.
- Monitoring antimicrobial resistance in Bordetella pertussis is crucial for effective treatment.
Purpose of the Study:
- To screen Finnish Bordetella pertussis isolates for resistance to macrolides, quinolones, and trimethoprim/sulfamethoxazole (SXT).
- To identify specific genetic mutations associated with macrolide and quinolone resistance.
Main Methods:
- Antimicrobial susceptibility testing was performed on 148 B. pertussis strains (2006-2017).
- Allele-specific PCR and gyrA gene sequencing were used to detect resistance mutations.
- Phenotypic testing included MIC determination (Etest) and disk diffusion assays.
Main Results:
- No macrolide resistance mutation (A2047G) or quinolone resistance mutation (A260G) was detected.
- All isolates showed susceptibility to azithromycin and erythromycin (MICs ≤0.25μg/mL).
- No resistance to nalidixic acid or SXT was observed based on inhibition zone sizes.
Conclusions:
- Allele-specific PCR is effective for screening macrolide resistance in B. pertussis.
- All Finnish B. pertussis isolates examined were susceptible to macrolides, quinolones, and SXT.
- Current treatment guidelines for pertussis in Finland remain effective against tested antimicrobials.
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