臺灣孵化場雛雞絨毛分離之大腸桿菌特性研究

Abstract

家禽大腸桿菌病是由家禽致病性大腸桿菌（APEC）引起的一種常見全身性傳染病，此病對家禽產業造成了嚴重的經濟損失。孵化場是商業雞場雞隻的主要來源，因此本研究試圖了解孵化場中是否存在大腸桿菌，以及了解其致病的可能性。為此，本研究在2016年10月到2017年11月之間，共收集2344份雛雞孵化器中的絨毛樣本進行實驗。在這些樣本中，大腸桿菌的總體發生率為2.0%，而每個孵化場大腸桿菌的發生率有所不同，最低為0%，最高達到16.9%，部分孵化場有如此之高的發生率，可以反映其在衛生管理方面的不足。除此之外，為了比較絨毛大腸桿菌和APEC在毒力因子、抗藥基因和抗藥性（最小抑菌濃度）方面的差異，本研究還收集了20株臨床病例分離到的APEC。從毒力因子的研究結果本研究發現，APEC更容易具有大部分的毒力因子（papC, astA, cvaC, hlyF, fyuA, iroN, iutA, iss, and ompT），這說明與APEC相比，絨毛大腸桿菌的致病可能性較低。但另一方面，絨毛大腸桿菌更容易具有與粘附相關的毒力因子fimC, 這說明絨毛大腸桿菌可能更容易粘附於家禽上呼吸道細胞。在抗藥性方面，全部的APEC和絨毛大腸桿菌都是多重抗藥性菌株，他們都對ampcilillin, amoxicillin, trimethoprim-sulfamethoxazole, cephalexin和florfenicol有抗藥性。就最小抑菌濃度的中位數而言，絨毛大腸桿菌對抗生素具有更高的感受性；但是這兩組菌株的抗藥基因檢測結果並沒有顯著性差異，這說明絨毛大腸桿菌仍然可能通過傳遞抗藥基因而造成公共衛生的危害。分子分型方面， XbaI脈衝場凝膠電泳（PFGE）結果顯示只有小部分的菌株擁有相同的圖譜，這說明孵化場污染來源的廣泛；一些具有相同PFGE圖譜的菌株是從同一孵化場分離到的，這意味著可能存在來自母雞群體的垂直傳播。總結以上，本研究結果顯示絨毛大腸桿菌相較於APEC而言，具有較低的致病性可能性。於此同時，本研究建議孵化場應注重消毒與清潔，從而減少絨毛中的大腸桿菌的存在。

Avian colibacillosis resulting from avian pathogenic Escherichia coli (APEC) seriously disrupts poultry production. Hatcheries are the main sources of chicken for commercial farms. To characterize the potential pathogenicity of E. coli strains isolated from hatcheries, 2,344 fluff samples from day-old chickens were collected from hatching incubators between October 2016 and November 2017. Among the hatcheries, the incidence of E. coli varied from 0 to 16.9%, with an overall incidence of 2.0%. High incidences reflected inadequate sanitation in some hatcheries. We also compared 20 clinically isolated APEC strains with fluff-originated E. coli in terms of expression of 10 virulence-associated genes (VAGs) and antimicrobial-resistance genes, and antimicrobial resistance using minimum inhibitory concentration (MIC) values. Our results showed that APEC more frequently expressed most of the assessed VAGs (papC, astA, cvaC, hlyF, fyuA, iroN, iutA, iss, and ompT), suggesting that fluff-originated E. coli is less likely to cause avian colibacillosis. However, fluff-originated E. coli more frequently expressed the adhesion gene fimC, which could confer higher upper respiratory tract adhesion. Both APEC and fluff-originated E. coli demonstrated multi-drug resistance, including 100% resistance to ampicillin, amoxicillin, trimethoprim-sulfamethoxazole, cephalexin, and florfenicol. Based on median MIC values, fluff-originated E. coli was more susceptible to antibiotics. However, resistance-gene expression did not significantly differ between groups, suggesting that fluff-originated E. coli should still be a public health concern. Molecular subtyping with XbaI-digested pulsed-field gel electrophoresis revealed that only a few strains showed identical patterns, indicating that a variety of contamination sources were present within individual hatcheries. Identical strains within the same hatchery may indicate vertical transmission from parent flocks. Overall, this is the first study to characterize fluff-originated E. coli. Our results suggest that it has lower pathogenicity than APEC and that thorough sanitation should be performed to reduce the occurrence of fluff-originated E. coli in hatcheries.