| Sumario: | The objective of this study was to determine Salmonella enteritidis phage type 13a (SE PT 13a) and Salmonella enteritidis biovar Issatschenko phage type 6a (SI) pathogenesis in 4 days old broiler chickens. Twenty-eight birds per treatment were inoculated with a dose of 1x10 (SE PT 13a) and 1x10 (SI), respectively, and fourteen chickens were inoculated with physiological saline solution (PSS) as negative controls. Samples from liver, spleen, heart, lung, crop, duodenum, jejunum, ileum and blind guts were taken during fourteen different times postinfection (6, 18, 30, 42, 54, 78, 102, 126, 150, 174, 198, 222, 246 and 270 hours postinfection (hpi) in order to obtain Salmonella spp isolation for bacteriological, histopathological and ultrastructural examination. During the first week, some depressed birds were observed, and the second week birds were found with yolk sac retention in both treatments. SE PT 13a was isolated at 18, 30, 42, 54, 78, 102, 126, 150, 174, 198, 246 and 270 hpi from all organs previously described. SI was isolated at 42, 150, 174 and 222 hpi, from crop, jejunum, ileum and blind gut samples. Ileum was the main organ where more frequently SE PT 13a and SI were isolated. There was no mortality in either treatments. Histopathology revealed inflammation, coagulative necrosis, congestion and hemorrhages in gastrointestinal tract (GIT) and visceral organs since 6 hpi in both treatments, with lesions from mild to severe. Ultrastructurally changes in enterocytes' cytoplasm: degeneration, necrosis, invasion and penetration of SE PT 13a and SI were observed. Results of this research showed the ability of SE PT 13a as well as SI to penetrate and invade enterocytes in experimentally infected broiler chicken, demonstrating that SI is able to infect broiler chickens and not only Muridae family.
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