Bordetella pertussisGram-negative pathogenic bacteria of the genus Bordetellathe causative agent of a contagious respiratory disease and whooping cough (whooping cough). The diphtheria-pertussis-tetanus (DPT) combination vaccine has significantly reduced pertussis-related illness and mortality, especially in infants (1). Macrolides represent a mostly natural polyketide class of products containing large macrocyclic lactone rings with potential linking groups (such as deoxy sugars) that have antibiotic or antifungal activity. Macrolides are popular medications frequently used to treat and prevent whooping cough. Macrolide resistance Bordetella pertussis (MRBP), characterized by the A2047G mutation in a region important for macrolide binding to the 23S rRNA gene, has recently emerged and spread worldwide (2). In China, the major MRBP gene lineage has shifted in the pertussis toxin promoter region (ptxP) allele type from ptxP1 to ptxP3and its prevalence ptxP3-Multilocus variable number tandem repeat analysis type (MT) 28 MRBP strains rapidly increased (3).

In Japan, the number of pertussis notifications, which decreased during the coronavirus pandemic, has increased significantly since 2024 (4). MRBP was first documented during the first quarantine in 2018. ptxP1-MT195-MRBP(5). Recently, ptxP3-MRBP strains isolated from Tokyo and Okinawa have been described, showing a close genetic relationship with Chinese strains (6,7).

MT27 is a single-locus MT28 variant, and this genotype carries virulence-associated alleles. ptxP3/ptxA1/prn2/fim3-1became predominant among macrolide-sensitive patients Bordetella pertussis (MSBP) Stocks from various countries including Japan (8–10). In contrast, only one MT27-MRBP strain has been reported in China in 2017 to date (8);No cases of infection have been confirmed outside of China. In this study, we report five MT27-MRBP strains isolated from children with pertussis at one hospital and two private clinics in Kobe City from February to March 2025 (table). To investigate the molecular epidemiological characteristics of these five MT27-MRBP isolates, we compared them with Japanese MT27-MSBP strains (including 10 Kobe City isolates) and Chinese MRBP strains isolated from 2010 to 2025 (3,6–8,10). This study was approved by the Kobe City Review Committee (approval number: SenR3-10).

We collected nine MT27 strains from patients aged 2 months to 12 years from January to March 2025 (table). All five MT27-MRBP strains carried the A2047G mutation in their 23S rRNA and exhibited MICs of >256 μg/mL for erythromycin, clarithromycin, and azithromycin. All patients infected with MT27-MRBP recovered without sequelae. BIGSdb-Pasteur platform (https://bigsdb.pasteur.fr/bordetella) to determine the MT27-MRBP virulence genotype, identical results were obtained for all strains. ptxP3/ptxA1/fhaB1/fim3–1/prn150. Among the five pathogenicity-related genes, prn Alleles between the MT27-MSBP and MT27-MRBP strains isolated in Kobe (i.e. prn2 MSBP and prn150 (in MRBP) (table). It should be noted that prn150 was identical to the allele of the globally circulating MT28-MRBP strain (3).

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shape. Phylogenetic tree based on single nucleotide mutations showing 15 MT27s Bordetella pertussisStrain isolated in Kobe (green). 37 stocks from Japan (yellow), including Tokyo (blue) and Okinawa (pink). And 155…

To determine genetic relatedness, we performed phylogenetic analysis using whole genome sequences of six MT27-MSBP isolates obtained in Kobe since 2013 (table) and other publicly available genomes (appendix table). Our single nucleotide variant-based phylogenetic analysis revealed that five MT27-MRBP strains were internally clustered. prn150 This strain is genetically closely related to the Chinese MRBP strain and its clonal population (shape). In addition, the MT27-MRBP strain from Kobe is the same as the MT27-MRBP strain from China (GenBank accession number SRR16306222), the Japanese MRBP strain BP636 from Tokyo (GenBank accession number DRR631445), and OkiPb01308 and OkiPb01309 (National Center for Biotechnology Information BioProject accession number PRJDB20292) from Okinawa (shape). The identification of genetically distinct strains across three geographically distant regions of Japan suggests multiple epidemiologically independent invasions. In contrast, MT27-MSBP strains KBP0014, KBP0018, KBP0019, and KBP0025 isolated in 2025 belonged to a clade of strains currently circulating in Japan. Taken together, our results suggest that MT27-MRBP is not derived from the MT27-MSBP currently circulating in Japan, but could potentially have been introduced from China. Finally, although the five MT27-MRBP-infected patients resided in three different wards, there was no obvious temporal link, suggesting that this newly emerged strain could potentially be spreading in Kobe.

In conclusion, clear genetic differences were identified between the MT27-MSBP and MT27-MRBP strains collected in Kobe from January to March 2025. Our study suggests that the MT27-MRBP strain, which is closely related to the Chinese MRBP strain, has emerged and is widespread in Kobe, Japan.

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