Characteristics of systemic infection and host responses in chickens experimentally infected with <i>Salmonella enterica</i> serovar Gallinarum biovar Gallinarum

Abstract

Salmonella enterica serovar Gallinarum biovar Gallinarum (S. Gallinarum) is a hostspecific pathogen causing systemic infection in poultry, which leads to significant economic losses due to high mortality. However, little is known about the dynamic process of systemic infection and pathogenic characteristics of S. Gallinarum in chickens. In the present study, we developed an oral infection model that reproduces the pathology of S. Gallinarum and clarified the host immune response of the infected chickens. Chickens at 20 days of age orally inoculated at a dose of 10 8 colony forming unit (CFU) showed typical clinical signs of fowl typhoid and died between 6 and 10 days post infection. The inoculated S. Gallinarum rapidly disseminated to multple organs and the bacterial counts increased in the liver and spleen at 3 days post infection.Pathological changes associated wirh inflammation in the liver and spleen became apparent at 4 days post infection, and increased expression of interferon (IFN)-γ and interleuikin (IL)-12 in the liver and spleen did not observed until 3 days post infection. These results indicate that S.Gallinarum rapidly spread to entire body through intestine, and the low-level of inflammatory responses in the liver during the early stage of infection may contribute to rapid, systemic dissemination of the bacteria. Our infection model and findings will contribute to the better understanding of the pathogenic mechanism of S. Gallinarum, and provide new insights into the prevention and control of fowl typhoid.

wecB Gene of Salmonella Gallinarum Plays a Critical Role in Systemic Infection of Fowl Typhoid

“…A previous study has reported that the most characteristic pathological lesions of fowl typhoid, such as hypertrophy, white lesions, and small necrotic foci, were observed in the liver of chickens (Ojima et al, 2021 ). In this study, we compared the pathological changes in the liver of chickens infected with wild-type and wecB ::Cm mutant strains.…”

“…We recently established an oral infection model and investigated the pathogenic characteristics and dynamic process of S . Gallinarum-induced systemic infection in vivo , mimicking the natural infection in chickens (Ojima et al, 2021 ). In this study, to reveal the pathogenic mechanism and understand the biological function of ECA of S .…”

“…Salmonella enterica serovar Gallinarum ( S . Gallinarum) 287/91, a spontaneous nalidixic acid-resistant strain (Ojima et al, 2021 ), was maintained in Luria-Bertani (LB) broth plus 30% glycerol at −80°C. Bacteria were routinely grown in LB broth (Eiken Chemical, Tokyo, Japan) at 37°C with shaking (at 150 rpm).…”

“…All efforts were made to minimize the suffering of the animals during the experiments. Female Boris Brown chickens, which are well known to be susceptible to salmonellosis (Smith, 1956 ; Ojima et al, 2021 ), were housed and provided water and food ad libitum . To ensure the chickens were free from Salmonella , fecal swabs were taken from the transport box for the bacteriological detection of Salmonella before experimental infection.…”

“…Gallinarum systemic infection in chicken, we constructed an ECA mutant strain ( wecB ::Cm) of S . Gallinarum and studied the biological function of ECA using our recently established model of systemic infection in chicken (Ojima et al, 2021 ). Our results demonstrate, for the first time, that disruption of the wecB locus can lead to bile salt and nalidixic acid sensitivity, and the resulting strains are significantly attenuated in the infected chickens in vivo .…”