Investigation of Genetic Variations in Virulence Factor Genes ptxC, tcfA, and fhaB of Bordetella pertussis Clinical Isolates and Vaccine Strains in Iran

Pertussis is an important vaccine preventable disease. It is still a major cause of infant morbidity and mortality in the world. Although the incidence of pertussis was successfully reduced after vaccination, the resurgence of pertussis has been reported in many countries even with high vaccination coverage. Genetic variation in virulence factors is one of the important causes for pertussis reemergence. We investigated genetic characteristics and allele types of 3 important virulence associated genes, including ptxC, tcfA, and fhaB in clinical B. pertussis isolates collected from different provinces of Iran and vaccine strains. Genomic DNA was extracted and ptxC, tcfA, and fhaB gene regions were amplified, using specific PCR primer. DNA sequencing was performed and data were analyzed. ptxC2, tcfA2, and fhaB1 were the dominant alleles with 87.5%, 97.5%, and 97.5% frequencies, respectively. Vaccine strains B. pertussis 134 and B. pertussis 509 contain the genotypes ptxC2- tcfA2-fhaB1 and ptxC2- tcfA2-fhaB1. Results for dominant alleles in ptxC2, tcfA2, and fhaB1 genes in Iran are consistent with dominant alleles of other countries such as Netherland, Finland, and Italy. It seems that ptxC2, tcfA2, and fhaB1 are the dominant circulating alleles in many countries after vaccination period, while vaccine strains have different alleles occasionally. More reported cases in recent years despite high coverage vaccination in Iran and genetic distances between clinical and vaccine strains suggest that antigenic changes in virulence factors possibly have an important role in the survival and evolution of the bacteria.