List of isolates and their characteristics.

Pathogenic Escherichia coli causes infections responsible for economic losses in animal herds worldwide. Although this bacterium is well studied in livestock and poultry, studies of camelid infections caused by extraintestinal pathogenic E. coli (ExPEC) are limited. In this study, a set of ExPEC from camel carcasses (n = 150) was characterized with respect to phylogenetic groups, 162 O serotypes, and 35 virulence-associated genes (VAGs) using PCR screening. ExPEC frequently belonged to phylogroup B1 (58.7%), followed by phylogroups C, A, and B2 (12.7%, 12.0%, and 9.3%, respectively). Additionally, the set of ExPEC contained 36 different serotypes. The ExPEC isolates were found to typically encode ≥5 tested VAGs, particularly those related to adhesion (afaI, fimA, pap, sfa, tsh), iron acquisition (fyuA, iroN, iucC, sitA), host cell damage (α-hly, cdt, cnf1, sat), invasion (ibeA), and bacterial protection (iss, ompT, traT). Moreover, ExPEC from camel adults and calves were different from each other. Among isolates from calves, prevalence was significantly higher for phylogroups C (q eitA, fepC, fyuA, iroN, iss, iucD, ompT, sitA), as well as VAGs with stronger link to pathogenicity (hlyF, and pap). To identify potential reservoir of camel ExPEC strains, fecal E. coli (n = 139) from healthy camels were also analyzed. Based on the identified characteristics, ExPEC were distinguishable from fecal isolates of healthy camels, suggesting an exogenous source of ExPEC infections, likely transmitted from wild birds and human keepers.致病性大肠杆菌（Pathogenic Escherichia coli）可引发全球家畜畜群感染并造成经济损失。尽管该菌在畜禽中的研究已较为充分，但针对肠外致病性大肠杆菌（ExPEC）引发骆驼科动物感染的相关研究仍较为有限。本研究通过PCR筛选技术，对150株取自骆驼胴体的肠外致病性大肠杆菌菌株进行了分型鉴定，涵盖系统发育群、162种O血清型以及35个毒力相关基因（VAGs）。该菌株群中，肠外致病性大肠杆菌主要隶属于系统发育群B1（占比58.7%），其次为C群、A群与B2群（占比分别为12.7%、12.0%与9.3%）。此外，本次研究的肠外致病性大肠杆菌菌株共涵盖36种不同的血清型。研究发现，多数肠外致病性大肠杆菌分离株携带至少5个经检测的毒力相关基因，尤其是与黏附相关的基因（afaI、fimA、pap、sfa、tsh）、铁摄取相关基因（fyuA、iroN、iucC、sitA）、宿主细胞损伤相关基因（α-hly、cdt、cnf1、sat）、侵袭相关基因（ibeA）以及细菌防护相关基因（iss、ompT、traT）。此外，成年骆驼与幼驼来源的肠外致病性大肠杆菌菌株存在显著差异。在幼驼来源的分离株中，系统发育群C的占比，以及eitA、fepC、fyuA、iroN、iss、iucD、ompT、sitA等基因的携带率显著更高；同时与致病性关联更为紧密的毒力基因hlyF与pap的携带率也显著提升。为明确骆驼源肠外致病性大肠杆菌菌株的潜在储存宿主，本研究同时对139株健康骆驼的粪便大肠杆菌分离株进行了分析。基于上述鉴定特征，骆驼源肠外致病性大肠杆菌与健康骆驼的粪便大肠杆菌分离株存在显著差异，提示肠外致病性大肠杆菌感染为外源获得性感染，其传播途径可能为野生鸟类与饲养人员。