The use of embryonic chicken eggs as an alternative model to evaluate the virulence of Salmonella enterica serovar Gallinarum

Abstract

Salmonella enterica serovar Gallinarum ( S . Gallinarum) can cause fowl typhoid, a severe systemic disease responsible for considerable economic losses. Chicken pathogenicity test is the traditional method for assessing the virulence of S . Gallinarum. However, this method is limited by several factors, including ethical considerations, costs, and the need for specialized facilities. Hence, we established a chicken embryo lethality assay (ELA) model to determine the virulence of S . Gallinarum. Three virulent and three avirulent representative strains, which were confirmed by the chicken pathogenicity test, were used to perform the ELA. The most significant difference between the virulent and avirulent strains could be observed when 13-day-old embryos were inoculated via the AC route and incubated for 5 days. Based on a 50% embryo lethal dose (ELD 50 ), isolates considered to be virulent had a Log 10 ELD 50 of ≤ 4.0, moderately virulent strains had a Log 10 ELD 50 of 4.0−6.1, and avirulent isolates had a Log 10 ELD 50 of ≥ 6.1. Different abilities to invade the liver of embryos were found between the virulent and avirulent strains by a growth curve experiment in vitro . The maximum colony-forming units (CFU) of the virulent strain was about 10,000 times higher than that of the avirulent strain in the liver at 5 days post infection. The ELA results of 42 field strains showed that thirty-two strains (76.2%) were virulent, nine were moderately virulent (21.4%), and one strain was avirulent (2.4%). In conclusion, these results suggest that the ELA can be used as an alternative method to assess the virulence of S . Gallinarum, which will contribute to the study of virulence genes, virulence evolution, pathogenic mechanisms and vaccine development.

Genomic Characterization of a Nalidixic Acid-Resistant Salmonella Enteritidis Strain Causing Persistent Infections in Broiler Chickens

“…SE_TAU19 achieved a 100% mortality rate compared to a virulent APEC strain which achieved an 80% mortality rate (Figure 2). SE_TAU19 virulence to broiler embryos was found to be comparable to published embryo lethality in Salmonella enterica serovar Gallinarum infections (56). This approach may be useful for future SE virulence or vaccine development studies.…”

Mechanistic insights of magnolol antimicrobial activity against Mycoplasma using untargeted metabolomic analyses

“…Previous study has reported that the magnolol exerted a low cytotoxicity in broilers, which can improve growth performance by modulating mucosal gene expression and the gut microbiota in the treatment of 300 mg/kg ( Chen et al., 2021 ). Chicken embryos were used as an infection model to evaluate the protection provided by magnolol as previously described with some modifications ( Helmy et al., 2020 ; Zhang et al., 2020 ). Briefly, Specific pathogen-free (SPF) chicken embryos were purchased from Merial-Vital, Beijing, China, and hatched in an environment of 37.5°C and 50–60% humidity.…”

Evaluation of Safety and Protective Efficacy of a waaJ and spiC Double Deletion Korean Epidemic Strain of Salmonella enterica Serovar Gallinarum

“…The treated chickens were observed twice a day for 2 weeks after administration. Clinical scores were determined and recorded using a system as we have previously described ( 25 ). Briefly, disease severity was scored as follows: 0, normal; 1, depression and ruffled feathers; 2, depression, ruffled feathers, and respiratory distress; 3, abovementioned clinical signs plus anorexia, emaciation, and green-yellowish diarrhea; and 4, death.…”

“…At the end of this period, all surviving chickens were euthanized. Clinical scores were determined and recorded following the method previously described ( 25 ).…”