Isolation of Brucella from a White’s tree frog (Litoria caerulea)

Abstract

Introduction: Brucellosis is a zoonotic disease that has a significant economic, social and public health impact in many parts of the world. The causative agents are members of the genus Brucella currently comprising 11 species and with an expanding known host range in recent years. Case presentation: One of a pair of White’s tree frogs (Litoria caerulea) developed skin lesions from which a pure growth of a haemolytic organism was obtained. The isolate was identified as Brucella melitensis by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, although the colony morphology was inconsistent with this identification. Applying the classical biotyping approach used to subdivide members of the genus Brucella, the isolate did not correspond to any known Brucella sp. However, PCR targeting of genes specific for members of the genus Brucella was strongly positive and 16S rRNA gene sequencing revealed a close relationship with extant Brucella spp. In order to place the isolate more accurately, a multilocus sequencing approach was applied, which confirmed that the isolate represented a novel member of the emerging ‘atypical’ Brucella group, which includes isolates from human disease, from rodents and, more recently, reported isolations from frogs in Germany. Conclusion: This case represents the first report of isolation of a Brucella sp. from frogs outside Germany and suggests that these isolates may be widespread. Whilst there is no evidence to date that these isolates represent a zoonotic threat, the association of other ‘atypical’ Brucella sp. with human disease suggests that appropriate measures should be taken to avoid unnecessary contact with potentially infected amphibians until the zoonotic potential of this group is better understood.