Identification and clinical significance of Bordetella holmesii isolated from a rare case of bacteremia in Nantong China

Abstract

Objective To analyze the identification, drug resistance and clinical significance of a rare bacterium of Bordetella holmesii (B.holmesii) to improve its detection and clinical diagnosis and treatment. Methods A strain isolated from a bacteremia case was identified by bacterial culture, biochemical tests and 16S rRNA gene sequencing. Mega 7.0 software was used to conduct a similarity analysis of 16S rRNA gene sequences between the type strains of Bordetella spp. and the isolate, and then a phylogenetic tree was constructed. Antibiotic resistance of the isolate was determined by E-test. Changes in bacterial growth were measured after adding different concentrations of riboflavin or its inhibitor lumiflavin to the culture medium. Results B. holmesii ABD2 was the pathogen causing bacteremia in the immunocompetent patient. It was deposited under the number of CGMCC 1.13721 in China General Microbiological Culture Collection Center (CGMCC), and the 16S rRNA gene sequences were deposited in National Center for Biotechnology Information (NCBI) with the accession number of KT828544.1. Unrooted tree showed that the B. holmesii strain was highly homologous with B. pertussis. Antibiotic susceptibility test showed that the minimum inhibitory concentrations (MIC) of piperacillin, ceftazidime, cefepime, imipenem, meropenem, ciprofloxacin, levofloxacin, gentamicin, amikacin, erythromycin, tetracycline and polymyxin B against the isolate were low, while the MIC values of cefazolin, cefuroxime, cefoxitin, cefotaxime, aztreonam and trimethoprim-sulfamethoxazole were high. Riboflavin accelerated the growth of B. holmesii ABD2, while its inhibitor lumiflavin had an inhibitory effect. Conclusions As B. holmesii is hard to isolate and identify, limited clinical, microbiological and epidemiological data are available. It is an under-recognized pathogen with a considerable amount of information that remains to be studied. Key words: Bordetella holmesii; Bacteremia; Immunocompetence; 16S rRNA gene sequencing; Riboflavin; lumiflavin