Abstract:
Objective To compare genetic characteristics of Bordetella pertussis isolates from child patients in Xishuangbanna, Yunnan province with those of vaccine isolate and Bordetella pertussis isolates from patients of other regions for providing evidence to pertussis prevention and control.
Methods Four Bordetella pertussis strains (named BP-L1, BP-L2, BP-L3, BP-L4) were isolated from nasopharyngeal swab specimens of child pertussis patients in the People′s Hospital of Xishuangbanna Prefecture, Yunnan province during October – December 2019 and the whole genome of the isolated strains were sequenced; the ptxP, ptxA, prn, fim3 genotype of the isolated strains were determined with MegAlign 7.1.0. According to the gene sequences published in National Center for Biotechnology Information (NCBI) database, the genotypes of the isolated strains were compared with those of CS strain of acellular pertussis vaccine innoculated in China and of the Bordetella pertussis strains prevalent in other countries and regions. Phylogenetic trees were constructed using RAxML software based on single nucleotide polymorphism (SNP) of 28 Bordetella pertussis strains.
Results Gene rearrangement due to 33 – 36 insertion sequences of the four isolated strains were identified in comparison with those of the CS strain. The similarity between ptxP, ptxA, prn, fim3 gene sequence of the isolated strains and CS strain was 99.2% – 100%. The results of phylogenetic tree showed that CS strain and reference strain TohamaⅠ clustered into a branch and formed an independent evolutionary branch. In recent years, Bordetella pertussis, which is prevalent in the world, can be divided into two clusters; the isolated BP-L1 and BP-L4 were clustered with the Bordetella pertussis prevalent in most European and American countries, which mainly included ptxP3/ptxA1/prn2 strains; while, the isolated BP-L2 and BP-L3 were clustered with Bordetella pertussis inducing endemic in Asia and mainly including ptxP1/ptxA1/prn1 strains.
Conclusion Compared with the vaccine strains, the main virulence protein genes and evolutionary branches of the Bordetella pertussis strains clinically isolated in Xishuangbanna, Yunnan province changed significantly and the changes are consistent with the genetic evolution trend of the Bordetella pertussis prevalent globally in recent years.
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