ABSTRACT
Objective:To identify and characterize two Balneatrix alpica strains isolated from a patient′s blood sample (strain X117) and the natural hot spring water in the patient′s residential district (strain GN-1), and to provide experimental evidence for the pathogenic diagnosis of clinical infection caused by this rare pathogen. Methods:Biochemical phenotypic identification, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), 16S rRNA gene sequencing, phylogenetic analysis, single-nucleotide polymorphism (SNP) analysis, and genome-wide analysis were performed to accurately determine the taxonomic status of the isolates X117 and GN-1 by using Balneatrix alpica DSM 16621 T as a reference. Microdilution broth method was used to test their antimicrobial susceptibility. The virulence genes carried by them were annotated and analyzed using the virulence factor database (VFDB). Results:Strains X117 and GN-1 formed light yellow or tan colonies with mottled surfaces on Columbia blood agar and chocolate agar plates after 4 d of culture. They were Gram-negative rods and positive for oxidase and indole tests, which were consistent with the characteristics of Balneatrix alpica DSM 16621 T. The phylogenetic analysis based on the 16S rRNA gene showed that the isolates X117 and GN-1 were both Balneatrix alpaca. The average nucleotide identity (ANI) values between the two isolates and Balneatrix alpica DSM 16621 T were 98.44% and 98.41%, respectively, and the digital DNA-DNA hybridization (dDDH) values were both 87.1%. The SNP distance between the two strains was 13, indicating that X117 and GN-1 might belong to the same clone. The antibiotic susceptibility testing showed that all of the three Balneatrix alpica strains were sensitive to the commonly used antibiotics against Gram-negative rods. The virulence genes carried by the three Balneatrix alpica strains were mainly involved in adhesion, invasion, flagella and biofilm formation. Conclusions:This study identified a case of bloodstream infection caused by Balneatrix alpica which was closely related to natural hot spring water. Natural hot spring water migh be an important source of clinical infections caused by this species.