Macrolide resistance trajectories across three Bordetella pertussis genetic backgrounds under stepwise erythromycin exposure

Background: remains a clinical concern, yet how broader genomic background may be associated with resistance-associated trajectories under antibiotic exposure is not fully understood. Methods: We performed stepwise erythromycin (ERY) induction using three clinical macrolide-susceptible parental isolates representing clinically relevant genetic backgrounds. Resistance-associated variants were tracked by whole-genome sequencing together with phenotypic readouts, including antimicrobial susceptibility testing, growth and biofilm assays, and ELISA-based measurements of selected virulence- and metabolism-associated factors. Results: conditions used. Conclusion: Under a controlled induction regimen, three representative clinical genomic backgrounds exhibited divergent macrolide-resistance trajectories and accompanying phenotypic differences. These observations are consistent with background-linked differences in resistance evolution and provide a basis for future validation in replicated evolution experiments.