The present study describes an experimental infection model for avian pathogenic Escherichia coli (APEC)-induced egg peritonitis in layer chickens. First, a pilot study which consisted of two separate experiments was carried out to compare two routes of inoculations of APEC to induce peritonitis and to examine if the presence of egg yolk in the peritoneum would facilitate APEC-induced peritonitis. This study showed that the presence of egg yolk in the peritoneum facilitated the development of egg peritonitis when the APEC was inoculated via the intra-uterine (IU) route. Based on the results of the pilot study, 56-wk-old white leghorn hens were divided into two groups of five chickens, Group G (inoculated with E. coli APECO78 strain) and Group H (control). Both groups were inoculated with 2–3 ml of egg yolk via the intraperitoneal route (IP). Subsequently, hens in Group H were inoculated with only egg yolk whereas the hens in Group G were inoculated with 1 × 109 colony-forming units of APECO78 bacteria via the IU route. Parameters such as mortality, clinical signs (anorexia, depression, and egg production efficiency), gross lesion scores, bacterial loads in internal organs, and histopathology of ovary and oviduct were assessed to evaluate the success of the infection model. Group G showed 40% acute mortality, severe depression, and anorexia with markedly reduced egg production and developed peritonitis-associated lesions such as accumulation of yellowish caseous fluid in the peritoneum, salpingitis, and oophoritis. Histopathologically, ovarian and oviduct tissues from group G exhibited severe inflammatory changes such as infiltration of mononuclear cells and edema. Group G also showed significant bacterial loads in the peritoneum, ovary, and oviduct. Interestingly, deceased birds from group G had also developed mild perihepatitis and pericarditis with heavy bacterial loads in the internal organs. On the other hand, group H birds did not exhibit any of the clinical signs and remained healthy until the end of the experiment. To summarize, our results demonstrate that IP administration of egg yolk followed by IU inoculation of APECO78 induced peritonitis in laying hens. Experimental infection models are often required to understand the mechanisms of disease pathogenesis. Therefore, the present infection model will aid in the studies of pathogenesis of layer peritonitis caused by APEC and in evaluating vaccine candidates to control the disease.
Modelo de infección experimental para la peritonitis por yema de huevo asociada a Escherichia coli en gallinas de postura.
El presente estudio describe un modelo de infección experimental para la peritonitis por yema de huevo inducida por cepas patógenas para las aves de Escherichia coli (APEC) en gallinas ponedoras. En primer lugar, se llevó a cabo un estudio piloto que consistía en dos experimentos separados para comparar dos rutas de inoculación de E. coli patógena en aves para inducir peritonitis y para examinar si la presencia de la yema de huevo en el peritoneo facilitaba la peritonitis inducida por E. coli. Este estudio mostró que la presencia de yema de huevo en el peritoneo facilitó el desarrollo de peritonitis cuando E. coli se inoculó a través de la ruta intrauterina (IU). Con base en los resultados del estudio piloto, gallinas de 56 semanas de edad se asignaron a dos grupos de cinco pollos, el grupo G (inoculado con la cepa APECO78 de E. coli) y el Grupo H (control). Ambos grupos se inocularon con 2 a 3 ml de yema de huevo a través de la vía intraperitoneal. Posteriormente, las gallinas del Grupo H se inocularon sólo con yema de huevo mientras que las gallinas en el Grupo G se inocularon con 1 × 109 unidades formadoras de colonias de la cepa APECO78 a través de la ruta intrauterina. Se evaluaron parámetros como mortalidad, signos clínicos (an
