Boyd Orr Centre for Population and Ecosystem Health, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G61 1QH, United Kingdom.
Appl Environ Microbiol. 2010 Dec;76(24):8110-6. doi: 10.1128/AEM.01343-10. Epub 2010 Oct 15.
The severity of human infection with pathogenic Escherichia coli depends on two major virulence determinants (eae and stx) that, respectively, produce intimin and Shiga toxin. In cattle, both may enhance colonization, but whether this increases fitness by enhancing cattle-to-cattle transmission in the field is unknown. In E. coli O157, the almost uniform presence of the virulence determinants in cattle isolates prevents comparative analysis. The availability to this study of extensive non-O157 E. coli data, with much greater diversity in carriage of virulence determinants, provides the opportunity to gain insight into their potential impact on transmission. Dynamic models were used to simulate expected prevalence distributions for serogroups O26 and O103. Transmission parameters were estimated by fitting model outputs to prevalence data from Scottish cattle using a Bayesian Markov chain Monte Carlo (MCMC) approach. Despite similar prevalence distributions for O26 and O103, their transmission dynamics were distinct. Serogroup O26 strains appear well adapted to the cattle host. The dynamics are characterized by a basic reproduction ratio (R(0)) of >1 (allowing sustained cattle-to-cattle transmission), a relatively low transmission rate from environmental reservoirs, and substantial association with eae on transmission. The presence of stx(2) was associated with reduced transmission. In contrast, serogroup O103 appears better adapted to the noncattle environment, characterized by an R(0) value of <1 for plausible test sensitivities, a significantly higher transmission rate from noncattle sources than serogroup O26, and an absence of fitness benefits associated with the carriage of eae. Thus, the association of eae with enhanced transmission depends on the E. coli serogroup. Our results suggest that the capacity of E. coli strains to derive fitness benefits from virulence determinants influences the prevalence in the cattle population and the ecology and epidemiology of the host organism.
人类感染致病性大肠杆菌的严重程度取决于两种主要的毒力决定因素（eae 和 stx），它们分别产生肠细胞黏附素和志贺毒素。在牛中，这两种因素都可能增强定植，但这是否通过增强田间牛与牛之间的传播来提高适应性尚不清楚。在大肠杆菌 O157 中，毒力决定因素在牛分离株中的几乎普遍存在阻止了比较分析。本研究可获得广泛的非 O157 大肠杆菌数据，这些数据中携带毒力决定因素的多样性更大，为深入了解它们对传播的潜在影响提供了机会。动态模型用于模拟血清群 O26 和 O103 的预期流行分布。使用贝叶斯马尔可夫链蒙特卡罗（MCMC）方法，通过拟合模型输出到苏格兰牛的流行数据来估计传播参数。尽管 O26 和 O103 的流行分布相似，但它们的传播动态是不同的。血清群 O26 菌株似乎很好地适应了牛宿主。动力学的特征是基本繁殖数（R(0)）大于 1（允许持续的牛与牛之间的传播），从环境储库传播的速度相对较低，并且与传播中的 eae 密切相关。stx(2) 的存在与传播减少有关。相比之下，血清群 O103 似乎更好地适应非牛环境，其 R(0)值对于合理的测试灵敏度小于 1，从非牛来源的传播率明显高于血清群 O26，并且与携带 eae 无关的适应性优势。因此，eae 与增强传播的关联取决于大肠杆菌血清群。我们的研究结果表明，大肠杆菌菌株从毒力决定因素中获得适应性优势的能力会影响牛群的流行程度以及宿主生物体的生态和流行病学。
