Detection and characterisation of Bordetella hinzii in line-related bacteraemia and respiratory tract infection in Australia.

Bordetella hinzii has emerged as an unusual cause of infection in immunocompromised patients, previously linked to zoonotic transmission. Antimicrobial susceptibility and genetic diversity of B. hinzii are poorly understood. This study reports phenotypic and genomic characteristics of the first four Australian isolates of B. hinzii obtained from elderly immunocompromised patients. Bordetella hinzii isolates were identified by MALDI-TOF and whole genome sequencing (WGS). Antibiotic susceptibility testing was performed using disk diffusion or E-test. Genomes of B. hinzii were analysed in global context. A phylogenetic tree was constructed of all isolates using Roary and a maximum-likelihood tree was generated from the core-snp alignment. Bordetella hinzii minimum inhibitory concentrations (MICs) were largely uniform with high MICs to ampicillin, ceftriaxone and ciprofloxacin and low MICs to meropenem and piperacillin-tazobactam. Genomic analysis of isolate sequences divided strains analysed into two phylogenetically distinct groups, with one Australian B. hinzii isolate (AUS-4) assigned to Group 1, and the remaining isolates (AUS1-AUS3 and AUS-5) to Group 2. Single nucleotide polymorphism (SNP) analysis revealed two isolates, AUS-1 and AUS-2, were closely related with 14 SNP differences between them. All other Australian isolates were unrelated to each and all other isolates from the international dataset. Bordetella hinzii appears to pose a risk to immunocompromised individuals but remains susceptible to extended spectrum β-lactam and carbapenem antibiotics. Genomic analysis suggested a dissemination of genetically distinct strains.