Isolation of Brucella inopinata from a White's tree frog (Litoria caerulea): pose exotic frogs a potential risk to human health?

Holger C Scholz; Kim O Heckers; Sandra Appelt; Dorothee Geier-Dömling; Patrick Schlegel; Alice R Wattam

doi:10.3389/fmicb.2023.1173252

Isolation of Brucella inopinata from a White's tree frog (Litoria caerulea): pose exotic frogs a potential risk to human health?

Front Microbiol. 2023 Jun 8:14:1173252. doi: 10.3389/fmicb.2023.1173252. eCollection 2023.

Authors

Holger C Scholz¹, Kim O Heckers², Sandra Appelt¹, Dorothee Geier-Dömling², Patrick Schlegel³, Alice R Wattam⁴

Affiliations

¹ Department of Bacteriology and Toxinology, Bundeswehr Institute of Microbiology, Munich, Germany.
² LABOklin GmbH and Co KG, Labor für klinische Diagnostik, Bad Kissingen, Germany.
³ Kleintierpraxis Dr. med vet. Patrick Schlegel, Sargans, Switzerland.
⁴ Biocomplexity Institute, University of Virginia, Charlottesville, VA, United States.

Abstract

Introduction: Cold-blooded hosts, particularly exotic frogs, have become a newly recognized reservoir for atypical Brucella species and strains worldwide, but their pathogenicity to humans remains largely unknown. Here we report the isolation and molecular characterization of a B. inopinata strain (FO700662) cultured from clinical samples taken from a captive diseased White's Tree Frog (Litoria caerulea) in Switzerland. The isolation of B. inopinata from a frog along with other reports of human infection by atypical Brucella raises the question of whether atypical Brucella could pose a risk to human health and deserves further attention.

Methods: The investigations included histopathological analysis of the frog, bacterial culture and in-depth molecular characterization of strain FO700662 based on genome sequencing data.

Results and discussion: Originally identified as Ochrobactrum based on its rapid growth and biochemical profile, strain FO700622 was positive for the Brucella- specific markers bcsp31 and IS711. It showed the specific banding pattern of B. inopinata in conventional Bruce-ladder multiplex PCR and also had identical 16S rRNA and recA gene sequences as B. inopinata. Subsequent genome sequencing followed by core genome-based MLST (cgMLST) analysis using 2704 targets (74% of the total chromosome) revealed only 173 allelic differences compared to the type strain of B. inopinata BO1^T, while previously considered the closest related strain BO2 differed in 2046 alleles. The overall average nucleotide identity (ANI) between the type strain BO1^T and FO700622 was 99,89%, confirming that both strains were almost identical. In silico MLST-21 and MLVA-16 also identified strain FO700662 as B. inopinata. The nucleotide and amino acid-based phylogenetic reconstruction and comparative genome analysis again placed the isolate together with B. inopinata with 100% support. In conclusion, our data unequivocally classified strain FO700622, isolated from an exotic frog, as belonging to B. inopinata.

Keywords: Brucella inopinata; atypical Brucella; exotic frogs; genomics; public health.