Molecular epidemiology and increasing macrolide resistance of Bordetella pertussis isolates in Guangzhou, China.

Background: Pertussis (whooping cough), a highly contagious respiratory disease caused by Bordetella pertussis, has resurged worldwide and requires increased attention. This study aimed to characterize the molecular epidemiology and antimicrobial susceptibility profiles of B. pertussis isolates circulating in Guangzhou, China.

Methods: A total of 91 culture-confirmed pertussis cases in Guangzhou between January 2020 and August 2024 were enrolled and studied. B. pertussis isolates (from January 2020 to May 2024) were recovered from 62 cases. All isolates underwent antigenic genotyping and phylogenetic analysis based on whole-genome sequencing. Antimicrobial susceptibility testing using E-test was performed on 12 representative isolates.

Results: The majority of culture-confirmed cases occurred in children under 1 year of age who were unvaccinated or partially vaccinated. Genotypic analysis revealed a significant shift: only 3 isolates (all from 2022) harbored the ptxP1 allele, while the remaining 59 exhibited ptxP3. Three types of pertactin (prn) allele were identified: prn1 (4.84%, 3/62), prn2 (11.29%, 7/62), prn150 (80.65%, 50/62), and 2 untyped prn allele. By 2024, prn150 became the predominant allele. Phylogenetic analysis revealed distinct branches separating ptxP1 and ptxP3 lineages. E-test results demonstrated that all macrolide-resistant isolates (exhibiting MICs > 256 mg/L for erythromycin, azithromycin, and clarithromycin) carried the A2047G mutation in 23S rRNA gene. The proportion of isolates harboring this mutation increased significantly after 2022 and dominated by 2024. All tested isolates displayed low MICs to alternative agents: trimethoprim/sulfamethoxazole (MICs ≤ 0.5/9.5 mg/L), cefoperazone/sulbactam (MICs ≤ 0.064/0.032 mg/L), and piperacillin/tazobactam (MICs ≤ 0.064/4 mg/L). Notably, macrolide-resistant isolates harboring ptxA1-ptxP3-prn150 genotype formed a distinct sub-clone within the ptxP3 clade.

Conclusions: Our findings demonstrate the current dominance of macrolide-resistant B. pertussis strain harboring ptxP3 and prn150 in Guangzhou since 2024. This study provides epidemiological and microbiological insights to guide local pertussis control strategies and to offer antimicrobial resistance monitoring efforts.