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 wa s performed. From 1995 through 1998, we isolated B. holmesii from 32 nasoph aryngeal specimens that had been submitted from patients suspected of havin g pertussis, Previously, B. holmesii had been associated mainly with septic emia 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 nasophar yngeal specimens. B. holmesii isolates were characterized for drug sensitiv ities and for genetic relatedness by pulsed-field gel electrophoresis (PFGE ), These isolates, an additional strain of B. holmesii isolated from a bloo d culture and previously confirmed by the Centers for Disease Control and P revention, Atlanta, Ga., and 14 other clinical isolates of Bordetella spp., including 4 of B. bronchiseptica, 5 of B. parapertussis, and 5 of B. pertu ssis, were studied. They were all separately inoculated on three Bordet Gen gou (BG) selective media containing either 0.625 mu g of oxacillin per ml, 40 mu g of cephalexin per ml, or 2.5 mu g of methicillin per ml, on BG agar with no antibiotic (control), and on charcoal agar (CA) with and without 4 0 mu g of cephalexin per ml, We found that cephalexin, the antibiotic commo nly 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 an alysis of the 32 B. holmesii isolates by PFGE following restriction with Xb aI and SpeI identified the dominant strains circulating during the study pe riod.