Recovery of Bordetella holmesii from patients with pertussis-like symptoms: use of pulsed-field gel electrophoresis to characterize circulating strains.

A 4-year retrospective study showing that we isolated Bordetella holmesii, but not Bordetella pertussis, from patients with pertussis-like symptoms was performed. From 1995 through 1998, we isolated B. holmesii from 32 nasopharyngeal specimens that had been submitted from patients suspected of having pertussis. Previously, B. holmesii had been associated mainly with septicemia and was not thought to be associated with respiratory illness. A study was undertaken to describe the characteristics of the B. holmesii isolates recovered and why we were successful in detecting the organism in nasopharyngeal specimens. B. holmesii isolates were characterized for drug sensitivities and for genetic relatedness by pulsed-field gel electrophoresis (PFGE). These isolates, an additional strain of B. holmesii isolated from a blood culture and previously confirmed by the Centers for Disease Control and Prevention, Atlanta, Ga., and 14 other clinical isolates of Bordetella spp., including 4 of B. bronchiseptica, 5 of B. parapertussis, and 5 of B. pertussis, were studied. They were all separately inoculated on three Bordet Gengou (BG) selective media containing either 0.625 microgram of oxacillin per ml, 40 microgram of cephalexin per ml, or 2.5 microgram of methicillin per ml, on BG agar with no antibiotic (control), and on charcoal agar (CA) with and without 40 microgram of cephalexin per ml. We found that cephalexin, the antibiotic commonly incorporated in both CA and BG agar for the recovery of Bordetella spp., is inhibitory to the growth of B. holmesii. In addition, the genotypic analysis of the 32 B. holmesii isolates by PFGE following restriction with XbaI and SpeI identified the dominant strains circulating during the study period.