AUTHOR=Scholz Holger C. , Heckers Kim O. , Appelt Sandra , Geier-Dömling Dorothee , Schlegel Patrick , Wattam Alice R. 

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

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1173252

DOI=10.3389/fmicb.2023.1173252

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p>Cold-blooded hosts, particularly exotic frogs, have become a newly recognized reservoir for atypical <italic>Brucella</italic> species and strains worldwide, but their pathogenicity to humans remains largely unknown. Here we report the isolation and molecular characterization of a <italic>B. inopinata</italic> strain (FO700662) cultured from clinical samples taken from a captive diseased White’s Tree Frog (<italic>Litoria caerulea</italic>) in Switzerland. The isolation of <italic>B. inopinata</italic> 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.</p></sec><sec><title>Methods</title><p>The investigations included histopathological analysis of the frog, bacterial culture and in-depth molecular characterization of strain FO700662 based on genome sequencing data.</p></sec><sec><title>Results and Discussion</title><p>Originally identified as <italic>Ochrobactrum</italic> based on its rapid growth and biochemical profile, strain FO700622 was positive for the <italic>Brucella-</italic> specific markers <italic>bcsp31</italic> and <italic>IS711</italic>. It showed the specific banding pattern of <italic>B. inopinata</italic> in conventional Bruce-ladder multiplex PCR and also had identical 16S rRNA and recA gene sequences as <italic>B. inopinata</italic>. 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 <italic>B. inopinata</italic> BO1<sup>T</sup>, while previously considered the closest related strain BO2 differed in 2046 alleles. The overall average nucleotide identity (ANI) between the type strain BO1<sup>T</sup> and FO700622 was 99,89%, confirming that both strains were almost identical. In <italic>silico</italic> MLST-21 and MLVA-16 also identified strain FO700662 as <italic>B. inopinata</italic>. The nucleotide and amino acid-based phylogenetic reconstruction and comparative genome analysis again placed the isolate together with <italic>B. inopinata</italic> with 100% support. In conclusion, our data unequivocally classified strain FO700622, isolated from an exotic frog, as belonging to <italic>B. inopinata</italic>.</p></sec>