RESUMEN
BACKGROUND: The emergence of macrolide resistance in Bordetella pertussis, the causative agent of pertussis, due to mutations in the 23S rRNA gene has been recently recognized. However, resistance mechanisms to macrolides in Bordetella parapertussis and Bordetella holmesii remain unknown. OBJECTIVES: This study investigated genomic changes induced by in vitro exposure to erythromycin in these three main pathogens responsible for pertussis-like disease. METHODS: A set of 10 clinical and reference strains of B. pertussis, B. parapertussis and B. holmesii was exposed to erythromycin for 15â weeks or 30 subculture passages. Antibiotic pressure was achieved by growth on the selective media with erythromycin Etest strips or impregnated discs. Genome polymorphisms and transcriptomic profiles were examined by short- and long-read sequencing of passaged isolates. RESULTS: B. parapertussis and B. holmesii isolates developed significant in vitro resistance to erythromycin (MIC >256â mg/L) within 2 to 7â weeks and at 5 to 12â weeks, respectively. B. pertussis remained phenotypically susceptible to the antibiotic following 15â weeks of exposure, with the MIC between 0.032 to 0.38â mg/L. Genomic analysis revealed that B. holmesii developed resistance due to mutations in the 23S rRNA gene. The resistance mechanism in B. parapertussis was hypothesized as being due to upregulation of an efflux pump mechanism. CONCLUSIONS: These findings indicate that both B. holmesii and B. parapertussis can be more prone to induced resistance following exposure to treatment with erythromycin than B. pertussis. The surveillance of macrolide resistance in Bordetella isolates recovered from patients with pertussis, especially persistent disease, is warranted.