乳房链球菌多位点序列分型和遗传进化特征分析

为探究中国不同地区来源的乳房链球菌（Streptococcus uberis，S.uberis）之间的多样性和遗传进化关系，本研究以部分地区分离到的38株乳房链球菌为研究对象，通过对其最小抑菌浓度（minimun inhibitory concentration，MIC）测定和全基因组框架测序，获取38株菌耐药性、耐药基因及毒力基因等相关信息；通过多位点序列分型技术（multilocus sequence typing，MLST）分析了7个管家基因的等位基因谱、序列型（sequence type，ST）和克隆复合体（clonal complexes，CCs），并构建系统进化树。MIC试验共采用15种抗生素，除头孢噻呋和氟苯尼考外，38株乳房链球菌对其中13种抗生素具有不同程度耐药，且江苏地区的耐药性明显强于新疆地区；耐药和毒力基因比对后发现，仅24株菌携带耐药基因，剩余14株则不携带耐药基因且属新疆地区分离株，与MIC试验结果相符；15种毒力基因中，除cfu、hasA/B和lbp外，余下12种毒力基因的携带率均高达100%。MLST结果表明，38株乳房链球菌共属于17个ST型，其中有15个ST型从未报道，仅supan01 1株菌属于ST-5 CCs。进化树结果揭示，38株分离株之间的亲缘性较远，分布呈地区依赖性，且中国部分地区当前流行的乳房链球菌与西方国家流行的菌株差异较大。本研究丰富了乳房链球菌的MLST分型数据库，为了解中国乳房链球菌遗传特性和分布特点提供了参考依据。

Analysis of Multilocus Sequence Typing and Genetic Evolution of Streptococcus uberis

The purpose of this study was to explore the diversity and genetic evolution of Streptococcus uberis (S.uberis) from different regions in China.In this study,38 strains of S.uberis isolated from some regions of China were used as the research objects.Through the determination of their minimum inhibitory concentration (MIC) and the sequencing of the whole genome frame,the related information of drug resistance,drug resistance gene and virulence gene of 38 strains were obtained.The alleles,sequence type (ST) and clone complexes (CCs) of 7 housekeeping genes were analyzed by multilocus sequence typing technique (MLST),and their evolutionary tree was established.A total of 15 antibiotics were used in MIC test,it was found that 38 strains of S.uberis were resistant to 13 antibiotics except for cefotaxime and florfenicol,and the drug resistance in Jiangsu province was significantly stronger than that in Xinjiang province.After comparison of resistance and virulence genes,only 24 strains were found to carry drug resistance genes,and the remaining 14 strains did not carry drug resistance genes and belonged to Xinjiang isolates,which was consistent with the results of MIC test.Among the 15 virulence genes,except for cfu,hasA/B and lbp,the carrying rate of the remaining 12 virulence genes was as high as 100%.Based on the MLST's results,38 strains of S.uberis belonged to 17 ST types,of which 15 ST types were not reported,and only 1 strain of supan01 belonged to ST-5 CCs.The phylogenetic tree results showed that the 38 isolates largely unrelated,and their distribution was region-dependent.Moreover,the phylogenetic tree results suggested that the S.uberis strains prevalent in some parts of China were largely different from those prevalent in Western countries.This study contributed to the MLST database of S.uberis and provided a reference basis for understanding of the genetic and distribution characteristics of S.uberis in China.