Genotypic analysis of antigenic determinant genes and the toxin gene of Bordetella pertussis strains isolated in Korea, 2013-2019

Kim Sohyeon, Lee Jin, Jung Sang Oun, Yoo Jaeil, Hwang Kyuhjam
Division of Bacterial Diseases, Center for Laboratory Control of Infectious Disease, KCDC

Whooping cough (or pertussis), caused by Bordetella pertussis infection, is a respiratory disease that is most severe in infants who are too young to be vaccinated or not yet completely vaccinated. Although vaccination was introduced in the 1950s, pertussis has remained an endemic disease. Moreover, epidemic outbreaks are reported periodically every 3 to 5 years in several countries despite their high vaccine coverages (e.g., in Australia, Netherlands, United Kingdom, and United States). In Korea, the incidence of pertussis has been on the increase since 2009, with 980 cases reported in 2018. One of the reasons for the increasing number of  pertussis cases is that the current strains have different genotypes than vaccine strain, with stronger promotors in pertussis toxin gene, resulting in toxin production. Therefore, we determined the multilocus sequence typing (MLST) genotypes and toxin gene promotor types in  in 61 B. pertussis strains isolated in Korea, 2013 to 2019. The major MLST genotype detected in the antigenic determinant genes was ST2, with 2 new minor genotypes also detected (ST9 and ST10). ST2 was different from the vaccine type and it was maintained as the major type prior to 2013. In these Korean isolates, a low level of allelic variation was observed only in the ptxS1, prn, and Fim3 genes. All strains tested in this study showed the ptxP3 genotype, which is associated with greater toxin production. In conclusion, we confirmed that the currently circulated B. pertussis strains show different genotypes from  the vaccine strain and have strong pertussis toxin gene promotors. In addition, the prevalence of a new variant type, recently reported in the pertactin gene, should be confirmed in future studies.

Keywords: Bordetella pertussis, Genotype, Multilocus sequence typing, Pertussis toxin promotor, Incidence, Prevalence