Prevalence and characterization of pertactin deficient Bordetella pertussis strains in Brazil, a whole-cell vaccine country

Many countries have reported antigenic divergence among circulating Bordetella pertussis strains, mainly in those countries which introduced the acellular pertussis (aP) vaccine. This phenomenon can be seen, for example, with the recent rise of pertactin (Prn)-deficient B. pertussis strains, one of the antigens included in aP vaccine formulas. The whole cell pertussis (wP) vaccine has been used in Brazil since 1977 for the primary pertussis, diphtheria and tetanus immunization series. In 2014, the aP vaccine was recommended for women during pregnancy to protect infants in the first months of life. Our objective was to determine the prevalence of Prn-deficiency in 511 isolates of B. pertussis collected in Brazil during 2010–2016. All isolates were characterized, through PFGE and serotyping, and screened for the loss of Prn by ELISA. Prn-deficiency was confirmed by immunoblotting, and identification of the possible genetic markers was performed with PCR and Sanger sequencing. Results indicate that 110 PFGE profiles are currently circulating, with five profiles representing the majority, and the predominant serotype 3, has been gradually replaced by serotype 2 and serotype 2,3. ELISA screening and immunoblotting identified three Prn-deficient isolates. Genotypic characterization by PCR and sequencing indicated that one isolate had a promoter mutation in prn, while the other two did not have an obvious genetic explanation for their deficiency. While the lack of Prn was identified in a few isolates, this study did not detect a relevant occurrence of Prn-deficiency, until 2016, confirming previous observations that Prn-deficiency is likely aP vaccine-driven.