Table 2_First genomic analysis of a Clostridium perfringens strain carrying both the cpe and netB genes and the proposal of an amended toxin-based typing scheme.xlsx

Clostridium perfringens strains are classified into seven toxinotypes (A–G) based on the profiles of the six typing toxin genes. Among these toxins, NetB is known as an important virulence factor for necrotic enteritis in chickens, and its gene, netB, is present only in type G strains. CPE is the enterotoxin that causes food-borne affections in humans, and its gene, cpe, is carried by type F strains and occasionally by type C, D, and E strains. However, strains with both netB and cpe are extremely rare; thus, they are not assigned to either toxinotype under the current typing scheme. In 2022, a 69-month-old female Holstein cow in Japan died suddenly, and a C. perfringens strain (CP280) possessing both netB and cpe was isolated for the first time in Japan from the bovine intestinal contents. The CP280 genome was composed of one chromosome and six circular plasmids, and netB and cpe were carried on different plasmids, pCP280-82k and pCP280-55k, respectively. Multilocus sequence typing analysis assigned CP280 to ST21, and all other reported ST21 strains were type G strains. In the phylogenetic analysis using the genomes of 553 C. perfringens strains, CP280 was clustered into a group along with the type G strains from affected birds. The deduced amino acid sequences of NetB and CPE from CP280 were identical to those of NetB and CPE from avian necrotic enteritis cases and human food poisoning cases, respectively, implying the potential of CP280 to cause these diseases. The genetic relatedness of CP280 and type G strains strongly suggests that CP280 was originally type G with the netB-positive plasmid pCP280-82k and later acquired the cpe-positive plasmid pCP280-55k; therefore, CP280 should be treated as a type G strain. We propose to change the requirement for this toxinotype in the toxin-based typing scheme from cpe(−) to cpe(+/−).

产气荚膜梭菌（Clostridium perfringens）菌株可根据6种分型毒素基因的谱型分为7个毒素型（A~G）。其中，NetB毒素是鸡坏死性肠炎的重要毒力因子，其编码基因netB仅存在于G型菌株中。CPE是引发人类食源性疾病的肠毒素，其编码基因cpe由F型菌株携带，偶尔也存在于C、D、E型菌株中。然而，同时携带netB和cpe的菌株极为罕见，因此在现行分型体系中无法将其归类至任一毒素型。2022年，日本一头69月龄的雌性荷斯坦奶牛突然死亡，研究人员首次从该牛的肠道内容物中分离到一株同时携带netB和cpe的产气荚膜梭菌菌株CP280。该菌株的基因组由1条染色体和6个环状质粒组成，netB与cpe分别位于质粒pCP280-82k和pCP280-55k上。多位点序列分型（multilocus sequence typing）分析将CP280划归至ST21型，而已报道的所有ST21型菌株均为G型菌株。在基于553株产气荚膜梭菌基因组的系统发育分析中，CP280与来自患病禽类的G型菌株聚为同一演化分支。CP280所编码的NetB与CPE的推导氨基酸序列，分别与禽类坏死性肠炎病例和人类食物中毒病例中的NetB、CPE序列完全一致，提示该菌株具备引发这两类疾病的潜在能力。CP280与G型菌株的遗传相关性强烈表明，该菌株最初为携带netB阳性质粒pCP280-82k的G型菌株，后续获得了携带cpe的阳性质粒pCP280-55k；因此，CP280应被归类为G型菌株。我们提议将基于毒素的分型体系中G型毒素型的判定要求从‘cpe(−)’修改为‘cpe(+/−)’。