Variation of Housekeeping Genes in Clinical Isolates and Vaccine Strains of Bordetella pertussis.

BACKGROUND

Bordetella pertussis causes serious contagious infections, primarily in childhood. A whole-cell vaccine, diphtheria-tetanus-whole cell pertussis (DTwP), has been used to protect against pertussis in children in Iran, but the pertussis cases have been increasing during recent years. We determined the allelic variation level of housekeeping genes in isolates recovered from pertussis patients and vaccine strains used in national vaccination program.

METHODS

Five clinical isolates, 2 vaccine strains and a Tohama I strain were studied through multilocus sequence typing (MLST) of housekeeping genes. The relatedness between STs, the founder, single- and double-locus variants (SLVs, DLVs) was determined using eBURST algorithm. The concordance between the type assignments by MLST and PFGE was determined.

RESULTS

In the 5 clinical isolates, 2 STs were identified, ST2 and ST79. The vaccine strains displayed two distinct allelic profiles assigned to ST1 and ST2. ST2 was predicted as founder and the remaining STs were SLVs of ST2. MLST and PFGE type assignments were 86.6% concordant.

CONCLUSIONS

The clinical isolates of B. pertussis were different from vaccine strains used in the national vaccination program. This study confirms the low level of variation in housekeeping genes of B. pertussis. MLST of virulent antigenic genes needs to be applied as a complementary method for the characterization of new ST-harboring isolates that may predominate periodically. The combination of these data allows rapid and efficient surveillance of currently circulating isolates. These data might elucidate the future trends and considerations for vaccine formulation and design.