Shiga toxin-producing Escherichia coli (STEC) is an important foodborne pathogen. Although most cases of STEC infection in humans are due to O157 and non-O157 serogroups, there are also reports of infection with STEC strains that cannot be serologically classified into any O serogroup (O-serogroup untypeable [OUT]). Recently, it has become clear that even OUT strains can be subclassified based on the diversity of O-antigen biosynthesis gene cluster (O-AGC) sequences. Cattle are thought to be a major reservoir of STEC strains belonging to various serotypes; however, the internal composition of OUT STEC strains in cattle remains unknown. In this study, we screened 366 STEC strains isolated from healthy cattle by using multiplex PCR kits including primers that targeted novel O-AGC types (Og types) found in OUT E. coli and Shigella strains in previous studies. Interestingly, 94 (25.7%) of these strains could be classified into 13 novel Og types. Genomic analysis revealed that the results of the in silico serotyping of novel Og-type strains were perfectly consistent with those of the PCR experiment. In addition, it was revealed that a dual Og8+OgSB17-type strain carried two types of O-AGCs from E. coli O8 and Shigella boydii type 17 tandemly inserted at the locus, with both antigens expressed on the cell surface. The results of this comprehensive analysis of cattle-derived STEC strains may help improve our understanding of the strains circulating in the environment. Additionally, the DNA-based serotyping systems used in this study could be used in future epidemiological studies and risk assessments of other STEC strains.

中文翻译：

---

从健康牛中分离的产志贺毒素大肠杆菌中新型 Og 类型的分布

产志贺毒素大肠杆菌(STEC) 是一种重要的食源性病原体。虽然大多数人类 STEC 感染病例是由 O157 和非 O157 血清群引起的，但也有报道称 STEC 菌株感染无法在血清学上归类为任何 O 血清群（O 血清群不可分型 [OUT]）。最近，很明显，甚至 OUT 菌株也可以根据 O 抗原生物合成基因簇 (O-AGC) 序列的多样性进行细分。牛被认为是属于各种血清型的 STEC 菌株的主要储存库；然而，牛体内 OUT STEC 菌株的内部组成仍然未知。在本研究中，我们使用多重 PCR 试剂盒筛选了从健康牛身上分离的 366 株 STEC 菌株，其中包括针对 OUT 中发现的新型 O-AGC 类型（Og 类型）的引物先前研究中的大肠杆菌和志贺氏菌菌株。有趣的是，这些菌株中的 94 个（25.7%）可分为 13 种新的 Og 类型。基因组分析表明，新型 Og 型菌株的计算机血清分型结果与 PCR 实验的结果完全一致。此外，发现双 Og8+OgSB17 型菌株携带来自大肠杆菌O8 和博伊氏志贺氏菌的两种类型的 O-AGC17 型串联插入该基因座，两种抗原均在细胞表面表达。对牛源性 STEC 菌株的综合分析结果可能有助于提高我们对在环境中传播的菌株的了解。此外，本研究中使用的基于 DNA 的血清分型系统可用于未来其他 STEC 菌株的流行病学研究和风险评估。