Characterisation of North American Brucella isolates from marine mammals

Extension of known ecological niches of Brucella has included the description of two novel species from marine mammals. Brucella pinnipedialis is associated predominantly with seals, while two major Brucella ceti clades, most commonly associated with porpoises or dolphins respectively, have been identified. To date there has been limited characterisation of Brucella isolates obtained from marine mammals outside Northern European waters, including North American waters. To address this gap, and extend knowledge of the global population structure and host associations of these Brucella species, 61 isolates from marine mammals inhabiting North American waters were subject to molecular and phenotypic characterisation enabling comparison with existing European isolates. The majority of isolates represent genotypes previously described in Europe although novel genotypes were identified in both B. ceti clades. Harp seals were found to carry B. pinnipedialis genotypes previously confined to hooded seals among a diverse repertoire of sequence types (STs) associated with this species. For the first time Brucella isolates were characterised from beluga whales and found to represent a number of distinct B. pinnipedialis genotypes. In addition the known host range of ST27 was extended with the identification of this ST from California sea lion samples. Finally the performance of the frequently used diagnostic tool Bruce-ladder, in differentiating B. ceti and B. pinnipedialis, was critically assessed based on improved knowledge of the global population structure of Brucella associated with marine mammals.布鲁氏菌属（Brucella）已知生态位的拓展已涵盖从海洋哺乳动物中分离得到的两个全新物种的报道。海豹布鲁氏菌（Brucella pinnipedialis）主要与海豹类宿主相关；目前已鉴定出两大主要的鲸类布鲁氏菌（Brucella ceti）演化支，二者分别最常与鼠海豚及海豚类宿主建立关联。截至目前，针对北欧水域以外（包括北美水域）的海洋哺乳动物来源布鲁氏菌分离株的表征研究仍较为有限。为填补这一研究空白，并拓展对这类布鲁氏菌物种的全球种群结构与宿主关联的认知，本研究对61株采自北美水域海洋哺乳动物的分离株开展了分子与表型鉴定，并将其与已有的欧洲分离株进行对比分析。绝大多数分离株的基因型为欧洲地区已有报道的类型，但在两大鲸类布鲁氏菌演化支中均发现了全新的基因型。研究发现竖琴海豹携带了此前仅见于冠海豹的海豹布鲁氏菌基因型，而该物种相关的序列型（STs）谱系呈现出丰富的多样性。本研究首次对白鲸来源的布鲁氏菌分离株完成了表征鉴定，发现其隶属于多种不同的海豹布鲁氏菌基因型。此外，本研究从加州海狮样本中鉴定出序列型ST27，进一步拓展了该序列型的已知宿主范围。最后，基于与海洋哺乳动物相关的布鲁氏菌全球种群结构的最新认知，本研究对常用诊断工具Bruce-ladder区分鲸类布鲁氏菌与海豹布鲁氏菌的性能进行了批判性评估。