Sequence Variation of the Pertussis Toxin S1 Subunit Encoding Gene in the Clinical Isolates of Bordetella pertussis in Iran

Whooping cough (pertussis) is an acute respiratory disease caused by Bordetella pertussis (B. pertussis). Pertussis toxin is an important virulence factor of B. pertussis and plays a major role in the immune and inflammatory responses. Likewise, allelic variations in the genes of virulence factors have led to the non-responsiveness of the new strains to both whole-cell and acellular vaccines. Given the importance of pertussis vaccine, we sought to address the lack of fundamental studies on the polymorphisms of the virulence genes of B. pertussis in Iran. The aim of this study was to identify the polymorphisms of the pertussis toxin S1 subunit (ptxS1) gene in the circulating strains and compare them to the vaccine strain. In this study, 50 strains of B. pertussis isolated from patients with pertussis were investigated in the pertussis reference laboratory of Pasteur institute of Iran. Cultivation, biochemical tests, and the specific antisera were used to confirm B. pertussis. The sequencing of the polymerase chain reaction products was performed to determine the ptxS1 alleles, and B. pertussis 134 was studied as the vaccine strain. The results showed that all the strains had the dominant allele ptxS1A. There were differences between the alleles of the clinical strains and the vaccine strain. In recent years, a significant increase in the incidence of pertussis has been reported worldwide. Our findings regarding the allelic shift of the ptxS1 gene are similar to those reported in many European and American countries showing the difference of the dominant allele of ptxS1 between the circulating isolates and the vaccine strains