[Analysis of antigenic gene characteristics and drug resistance of Bordetella pertussis in Liaoning Province from 2018 to 2024].

The antigenic and genetic characteristics and drug resistance of 10 Bordetella pertussis (Bp) isolates from Liaoning Province between 2018 and 2024 were analyzed. Based on whole-genome sequencing data, seven antigenic genotypes and 2, 047 mutation sites in the 23S rRNA gene of the 10 Bp isolates were analyzed and compared with those of vaccine strains. The results showed that all isolates shared the same fim2-1/fim3-1/tcfA2 genotype as the vaccine strains, while differences were observed in the ptxA, ptxP, prn, and fhaB genotypes; two prn-deficient strains were identified. Multilocus variable-number tandem-repeat (MLVA) analysis combined with antigenic genotype analysis revealed that two isolates carried the ptxP1-MT104 genotype and eight carried the ptxP3-MT28 genotype. Resistance gene prediction using the ResFinder and CARD databases revealed no acquired macrolide resistance genes encoding methyltransferases, efflux pumps, or drug-inactivating enzymes. The resistance mechanism in all isolates was the A2047G point mutation in the V region of the 23S rRNA gene. Phylogenetic analysis demonstrated that Liaoning Bp isolates were closely related to vaccine strains and to prevalent Bp strains from multiple countries and regions. The strains circulating in Liaoning from 2023 to 2024 showed close genetic proximity to recent dominant domestic strains (ptxP3-MT28-MRBP), whereas they exhibited greater genetic distance from earlier vaccine strains. The susceptibility of the isolates to eight antibacterial agents was tested using the E-test method. All isolates were resistant to macrolides (erythromycin, azithromycin, clarithromycin) but susceptible to levofloxacin, ampicillin, ciprofloxacin, trimethoprim-sulfamethoxazole, and ceftriaxone. Non-vaccine-type ptxP3-MT28 strains, accounting for 8/10 of all isolates in this study, showed resistance to macrolides, and all strains isolated since 2023 belonged to this genotype. Pertussis isolates in Liaoning Province have universally undergone antigenic drift and developed resistance to macrolides, among which non-vaccine-type ptxP3-MT28 strains have become the predominant circulating strains.