Abstract
Background and Aim: The studies about Salmonella infection in the newly hatched chicks were not extensive. The objective of this study was to determine pathogenicity of Salmonella enterica subspecies enterica serovar Enteritidis (SE) phage type (PT) 1 in one-day-old specific pathogen free (SPF) chicks.
Methods: Seventy, one-day-old SPF chicks, were divided into SE group (30 chicks), mortality group (10 chicks), both orally inoculated (1.0 mL) with SE PT1 (1x108 cfu per 1.0 mL), and one control group (30 chicks). The chicks were sacrificed at 6 and 12 hours, and days 1, 2, 3, 5, 7, 10, 14, and 21 post-inoculation (pi). Samples were collected for bacterial isolation, histological examination, and ultrastructural examination.
Results: Starting from day 2 pi, the body weight in SE group significantly (p< 0.05) decreased. The SE isolation percentages from the liver, spleen, midintestinal content, caecal content, caecal tonsil, blood and cloacal swab were 0.73, 0.77, 0.33, 0.33, 0.36, 0.40 and 0.30, respectively. The isolation percentage in the liver was significantly (p<0.05) higher than the blood and cloacal swab. The villi heights and crypt depths in SE group were significantly (p<0.05) greater and smaller, respectively.Ultrastructurally, erosion and necrosis were observed in the microvilli of the caecal tonsil.The bacteria was engulfed by macrophages at the interepithelial clefts of the M-like M cells.
Conclusion: It was concluded that the inoculation of SE phage type 1 in one-day-old chicks caused a systemic infection with diarrhoea, decrease in body weight and villi height in the duodenum, jejunum and ileum, and high bacterial loading in the liver with mild gross and histological lesions of organs, erosion and necrosis of microvilli and low mortality. The bacteria entered the body system from the intestinal tract through the interepithelial clefts of the M-like M cells of the caecal tonsil.

Key words: Salmonella enterica, phage type 1, SPF chicks, villi and crypt heights, lesions