Prevalence and Genetic Characterization of Pertactin-Deficient Bordetella pertussis in Japan

Abstract

The adhesin pertactin (Prn) is one of the major virulence factors of Bordetella pertussis, the etiological agent of whooping cough. However, a significant prevalence of Prn-deficient (Prn−) B. pertussis was observed in Japan. The Prn− isolate was first discovered in 1997, and 33 (27%) Prn− isolates were identified among 121 B. pertussis isolates collected from 1990 to 2009. Sequence analysis revealed that all the Prn− isolates harbor exclusively the vaccine-type prn1 allele and that loss of Prn expression is caused by 2 different mutations: an 84-bp deletion of the prn signal sequence (prn1ΔSS, n = 24) and an IS481 insertion in prn1 (prn1::IS481, n = 9). The frequency of Prn− isolates, notably those harboring prn1ΔSS, significantly increased since the early 2000s, and Prn− isolates were subsequently found nationwide. Multilocus variable-number tandem repeat analysis (MLVA) revealed that 24 (73%) of 33 Prn− isolates belong to MLVA-186, and 6 and 3 Prn− isolates belong to MLVA-194 and MLVA-226, respectively. The 3 MLVA types are phylogenetically closely related, suggesting that the 2 Prn− clinical strains (harboring prn1ΔSS and prn1::IS481) have clonally expanded in Japan. Growth competition assays in vitro also demonstrated that Prn− isolates have a higher growth potential than the Prn+ back-mutants from which they were derived. Our observations suggested that human host factors (genetic factors and immune status) that select for Prn− strains have arisen and that Prn expression is not essential for fitness under these conditions.

Pertussis Vaccine Effectiveness in the Setting of Pertactin-Deficient Pertussis

“…18,35 The rapid increase in pertactindeficient B pertussis in multiple countries, combined with evidence that several mutations can result in lack of pertactin, suggest pertactin deficiency may confer a selective advantage to the bacteria. 22,[38][39][40][41] More specifically, several recent studies indicate pertactin deficiency may especially benefit the bacteria among a highly immunized population. For instance, pertactindeficient strains were found to colonize mice primed with acellular pertussis vaccine more effectively than pertactin-expressing strains; a separate study found that acellular vaccinated individuals had twoto fourfold greater odds of being infected with a pertactin-deficient 5 rather than a pertactin-expressing B pertussis strain.…”

The History of Bordetella pertussis Genome Evolution Includes Structural Rearrangement

“…Although sequence diversity has also been observed in the vaccine immunogen pertactin (Prn), the circulating isolates recovered in the United States have become predominantly Prn deficient in recent years by one of at least 16 different mutations to the prn gene (16). The global emergence of Prn deficiency is well documented (16)(17)(18)(19), and deficiency may confer a fitness advantage during infection (20,21). While Prn deficiency appears to be more prevalent in isolates recovered from fully vaccinated patients, it does not appear to impact the effectiveness of acellular pertussis vaccines (22,23).…”

Resurgence of pertussis calls for re-evaluation of pertussis animal models

“…In France, Bouchez et al noted that a significant percentage (5.6%) of the strains from studied hospitalized newborns below 6 months of age did not produce Prn [45]. Recently, Otsuka et al reported that Prn-deficient strains have significantly increased in B. pertussis populations since the early 2000s in Japan [47]. Both countries have molecular surveillance systems in place and report stable pertussis vaccination coverage for primary series [47,202,203].…”

“…Recently, Otsuka et al reported that Prn-deficient strains have significantly increased in B. pertussis populations since the early 2000s in Japan [47]. Both countries have molecular surveillance systems in place and report stable pertussis vaccination coverage for primary series [47,202,203]. Antigenic mismatches between pertussis vaccine strains and circulating vaccine-evasive B. pertussis strains may alter the effectiveness of vaccine-induced immune responses through escape from immune recognition, as will be discussed below.…”

“…However, adaptation may also affect strain virulence properties or the biological impact of antigens, as is under investigation by several research groups. In preliminary studies, Prn-deficient strains were found to have competing growth advantage in vitro [47], but reduced multiplication in adult mice [45]. By producing 1.6-times more of the virulence factor and immune-modulating agent, Ptx, the emerging ptxP3 strains may alter the course or severity of an infection before the immune response can become effective [41].…”