Streptococcus suis (S. suis) is a gram-positive coccus that causes disease in humans and animals. The codon usage pattern of bacteria reveals a range of evolutionary changes that assist them to enhance tolerance to environments. To better understand the genetic features during the evolution of S. suis, we performed codon usage analysis. Nine pathogenic strains of different serotypes and different geographical distribution were analyzed to better understand the differences in their evolutionary process. Nucleotide compositions and relative synonymous codon usage (RSCU) analysis revealed that A/T-ending codons are dominant in S. suis. Neutrality analysis, correspondence analysis and ENC-plot results revealed that natural selection is the predominant element prompting codon usage. Cluster analysis based on RSCU was roughly consistent with the dendrogram rooted genomic BLAST analysis. Comparison of synonymous codon usage pattern between S. suis and susceptible hosts (H. sapiens and S. scrofa) revealed that the codon usage of S. suis is separated from the synonymous codon usage of susceptible hosts. The CAI values implied that S. suis includes a series of predicted highly expressed coding sequences contained in metabolism and transcriptional regulation, revealing the necessity of this pathogen to deal with various environmental conditions. The study of codon usage in S. suis may provide evidence involving the molecular evolution of bacteria and a better understanding of evolutionary relationships between S. suis and its corresponding hosts.

猪链球菌（S. suis）是一种革兰氏阳性球菌，可引起人类和动物疾病。细菌的密码子使用模式揭示了一系列进化变化，这些变化有助于细菌增强对环境的耐受性。为了更好地了解猪链球菌进化过程中的遗传特征，我们进行了密码子使用分析。分析了九种不同血清型和不同地理分布的致病菌株，以更好地了解其进化过程的差异。核苷酸组成和相对同义密码子使用（RSCU）分析表明，A / T末端密码子在猪链球菌中占主导地位。。中性分析，对应分析和ENC图结果显示，自然选择是促使密码子使用的主要元素。基于RSCU的聚类分析与基于树状图的基因组BLAST分析大致一致。猪链球菌和易感宿主（H. sapiens和S. scrofa）之间同义密码子使用方式的比较显示，猪链球菌的密码子使用与易感宿主的同义密码子使用是分开的。CAI值暗示猪链球菌包括代谢和转录调控中包含的一系列预测的高表达编码序列，揭示了这种病原体应对各种环境条件的必要性。对猪链球菌密码子使用的研究可能提供涉及细菌分子进化的证据，并且可以更好地了解猪链球菌与其相应宿主之间的进化关系。