Co-infections of <i>Enterococcus cecorum</i> and various avian pathogens resulted in varying rates of SPF broilers with an <i>E. cecorum</i> infection

<i>Enterococcus cecorum</i> infections can be experimentally reproduced after oral inoculation. Co-infections of <i>E. cecorum</i> with other avian pathogens might increase the proportion of broilers with <i>E. cecorum</i> infections. The aim of the study was to examine via which infection routes <i>E. cecorum</i> is capable of causing infections, and which co-infections exacerbate <i>E. cecorum</i> infections. Two experiments, each with 12 groups, were conducted. Per group, 40 SPF broilers were inoculated intravenously, orally or via aerosol with <i>E. cecorum</i> alone, a negative control group was included, and in eight groups the effect of co-infections was studied. In experiment 1, infectious bronchitis virus (IBV), Newcastle disease virus (NDV) vaccine, reovirus, and chicken anaemia virus (CAV) were inoculated before oral or aerosol challenge with <i>E. cecorum</i>. In experiment 2, <i>E. cecorum</i> was given after the administration of dexamethasone, or inoculation of CAV, or combinations of IBV or NDV with <i>Mycoplasma synoviae</i> (M.s.). Typical <i>E. cecorum</i> lesions were reproduced via all applied infection routes. The proportion of lesions was highest in the intravenously inoculated groups, being 0.25 (95% confidence interval (CI):0.127–0.412) and 0.275 (95% CI:0.146–0.439) in experiments 1 and 2, respectively. More lesions were observed in experiment 2, while the proportion of lesions after oral and aerosol inoculation did not differ in either experiment. The proportion of lesions was not exacerbated after co-infections of <i>E. cecorum</i> with various avian pathogens. Only the proportion of <i>E. cecorum</i> reisolations was exacerbated after inoculation with CAV or M.s. in combination with IBV or NDV. Typical <i>E. cecorum</i> lesions can be reproduced in SPF broilers after intravenous, aerosol and oral inoculations.The respiratory route is potentially an infection route for pathogenic <i>E. cecorum</i> bacteria.Co-infections tested in this study or dexamethasone do not exacerbate the proportion of <i>E. cecorum</i> lesions.M.s. in combination with IBV or NDV vaccines exacerbates the proportion of positive reisolations.Immunosuppression induced by early CAV infection increases the proportion of positive reisolations. Typical <i>E. cecorum</i> lesions can be reproduced in SPF broilers after intravenous, aerosol and oral inoculations. The respiratory route is potentially an infection route for pathogenic <i>E. cecorum</i> bacteria. Co-infections tested in this study or dexamethasone do not exacerbate the proportion of <i>E. cecorum</i> lesions. M.s. in combination with IBV or NDV vaccines exacerbates the proportion of positive reisolations. Immunosuppression induced by early CAV infection increases the proportion of positive reisolations.口服接种后可实验性复制粪肠球菌（<i>Enterococcus cecorum</i>）感染。粪肠球菌（<i>E. cecorum</i>）与其他禽类病原体的共感染可能会增加肉鸡中粪肠球菌感染的比例。本研究旨在探讨粪肠球菌（<i>E. cecorum</i>）可通过哪些感染途径引发感染，以及哪些共感染会加剧其感染。本研究开展了两项实验，每项实验包含12组。每组40只无特定病原体（SPF）肉鸡单独接受粪肠球菌（<i>E. cecorum</i>）的静脉、口服或气溶胶接种；实验还纳入了一个阴性对照组，并在8组中研究了共感染的效应。实验1中，在对肉鸡进行粪肠球菌（<i>E. cecorum</i>）口服或气溶胶攻击前，先接种传染性支气管炎病毒（IBV）、新城疫病毒（NDV）疫苗、呼肠孤病毒及鸡贫血病毒（CAV）。实验2中，在给予地塞米松（dexamethasone）、接种CAV，或接种IBV/NDV与滑膜支原体（<i>Mycoplasma synoviae</i>，M.s.）的组合后，再给予粪肠球菌（<i>E. cecorum</i>）。所有应用的感染途径均能复制出典型的粪肠球菌病变。静脉接种组的病变比例最高，实验1和实验2中分别为0.25（95%置信区间（CI）：0.127–0.412）和0.275（95% CI：0.146–0.439）。实验2中观察到更多病变，但口服和气溶胶接种后的病变比例在两项实验中均无差异。粪肠球菌与多种禽类病原体共感染后，病变比例并未加剧。仅在接种CAV或M.s.与IBV/NDV的组合后，粪肠球菌的再分离阳性比例有所增加。静脉、气溶胶及口服接种后，可在SPF肉鸡中复制出典型的粪肠球菌病变。呼吸道途径可能是致病性粪肠球菌的感染途径之一。本研究中测试的共感染或地塞米松并未加剧粪肠球菌病变的比例。M.s.与IBV或NDV疫苗的组合会增加再分离阳性的比例。早期CAV感染诱导的免疫抑制会增加再分离阳性的比例。静脉、气溶胶及口服接种后，可在SPF肉鸡中复制出典型的粪肠球菌病变。呼吸道途径可能是致病性粪肠球菌的感染途径之一。本研究中测试的共感染或地塞米松并未加剧粪肠球菌病变的比例。M.s.与IBV或NDV疫苗的组合会增加再分离阳性的比例。早期CAV感染诱导的免疫抑制会增加再分离阳性的比例。