Longitudinal Study of Avian Pathogenic <i>Escherichia coli</i> (APEC) serogroups associated with disease in Georgia poultry using molecular serology and virulence gene analysis.

Avian pathogenic <i>Escherichia coli</i> (APEC) is a significant cause of morbidity, mortality, and production loss to the poultry industry worldwide. Here, we characterized 569 <i>E. coli</i> isolates from avian-diagnosed colibacillosis cases from the state of Georgia, USA. A total of 339 isolates were assigned into 32 serogroups with the majority classifying as O78, O2, O25, O8, O1, O86, O18, and O15. Serogroup O25 was found to link with broilers, while broiler breeders were more often associated with serogroup O1 and pet/ hobby birds with serogroup O8. In addition, some serogroups (O1) were more prevalent in the Summer and Fall. Analysis for virulence-associated genes (VAGs) found 23.20% of isolates did not harbor any genes linked with the APEC pathotype, while ColV plasmid-associated genes (<i>iroN</i>, <i>ompT</i>, <i>hlyF</i>, <i>iss</i>, and <i>aerJ,</i>) were frequently detected among most isolates (with 80 to 96% prevalence) and some of these genes were linked with serogroup. Phylogenetic analysis, classified isolates into phylogenetic groups B2 (27%), G (21%), F (15%), and A (11%). The phylogenetic group B2 isolates also harbored the highest number of VAGs. This study highlights that the current APEC-causing disease in birds in the State of Georgia has identified several emerging serogroups possessing several VAGs that could potentially lead to challenges in colibacillosis control.禽致病性大肠杆菌（Avian pathogenic Escherichia coli, APEC）是全球家禽养殖业发病率、死亡率与生产损失的重要诱因。本研究对采自美国佐治亚州经禽类确诊的禽大肠杆菌病（colibacillosis）病例的569株大肠杆菌分离株进行了分型鉴定。其中339株分离株被划归至32个血清群，优势血清群为O78、O2、O25、O8、O1、O86、O18及O15。研究发现，血清群O25与肉鸡相关，肉种鸡则更常与血清群O1相关，而宠物/观赏禽多与血清群O8相关。此外，部分血清群（如O1）在夏季与秋季的检出率更高。毒力相关基因（virulence-associated genes, VAGs）分析显示，23.20%的分离株未携带任何与APEC致病型相关的基因；而ColV质粒相关基因（iroN、ompT、hlyF、iss及aerJ）在多数分离株中检出率达80%~96%，且部分此类基因与血清群存在关联。系统发育分析将分离株划分为B2（27%）、G（21%）、F（15%）及A（11%）四个系统发育群，其中系统发育群B2的分离株携带的毒力相关基因数量最多。本研究表明，当前美国佐治亚州禽类中由APEC引发的禽大肠杆菌病已检出多个携带多种毒力相关基因的新兴血清群，这可能给禽大肠杆菌病的防控带来挑战。