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

• Published in: Frontiers in microbiology 2023-06, Vol.14, p.1173252-1173252
• Main Authors: Scholz, Holger C, Heckers, Kim O, Appelt, Sandra, Geier-Dömling, Dorothee, Schlegel, Patrick, Wattam, Alice R
• Format: Article
• Language: English
• Subjects: atypical Brucella; Brucella inopinata; exotic frogs; genomics; Microbiology; public health
• ISSN: 1664-302X; 1664-302X
• DOI: 10.3389/fmicb.2023.1173252

Cold-blooded hosts, particularly exotic frogs, have become a newly recognized reservoir for atypical species and strains worldwide, but their pathogenicity to humans remains largely unknown. Here we report the isolation and molecular characterization of a strain (FO700662) cultured from clinical samples taken from a captive diseased White's Tree Frog ( ) in Switzerland. The isolation of 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. The investigations included histopathological analysis of the frog, bacterial culture and in-depth molecular characterization of strain FO700662 based on genome sequencing data. Originally identified as based on its rapid growth and biochemical profile, strain FO700622 was positive for the specific markers and . It showed the specific banding pattern of in conventional Bruce-ladder multiplex PCR and also had identical 16S rRNA and recA gene sequences as . 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 BO1 , while previously considered the closest related strain BO2 differed in 2046 alleles. The overall average nucleotide identity (ANI) between the type strain BO1 and FO700622 was 99,89%, confirming that both strains were almost identical. In MLST-21 and MLVA-16 also identified strain FO700662 as . The nucleotide and amino acid-based phylogenetic reconstruction and comparative genome analysis again placed the isolate together with with 100% support. In conclusion, our data unequivocally classified strain FO700622, isolated from an exotic frog, as belonging to .