Evaluation of pathogenicity of Salmonella Gallinarum strains harbouring deletions in genes whose orthologues are conserved pseudogenes in S. Pullorum

Abstract

The diseases caused by Salmonella Gallinarum and S. Pullorum in chickens known as fowl typhoid and pullorum disease, respectively, pose a great threat to the poultry industry mainly in developing countries, since they have already been controlled in the developed ones. These bacteria are very similar at the genomic level but develop distinct host-pathogen relationships with chickens. Therefore, a deep understanding of the molecular mechanisms whereby S. Gallinarum and S. Pullorum interact with the host could lead to the development of new approaches to control and, perhaps, eradicate both diseases from the chicken flocks worldwide. Based on our previous study, it was hypothesised that metabolism-related pseudogenes, fixed in S. Pullorum genomes, could play a role in the distinct host-pathogen interaction with susceptible chickens. To test this idea, three genes (idnT, idnO and ccmH) of S. Gallinarum str. 287/91, which are pseudogenes on the S. Pullorum chromosomes, were inactivated by mutations. These genetically engineered strains grew well on the solid media without any colony morphology difference. In addition, similar growth curves were obtained by cultivation in M9 minimal medium containing D-gluconate as the sole carbon source. Infection of chickens with idnTO mutants led to increased numbers of bacteria in the livers and spleens at 5 days post-infection, but with slightly decreased heterophil infiltration in the spleens when compared to the wild-type strain. On the other hand, no significant phenotypic change was caused by mutation to ccmH genes. Apart from the above-mentioned alterations, all S. Gallinarum strains provoked similar infections, since mortality, clinical signs, macroscopic alterations and immune response were similar to the infected chickens. Therefore, according to the model applied to this study, mutation to the idnTO and ccmH genes showed minor impact on the fowl typhoid pathogenesis and so they may be relics from the ancestor genome. Our data hints at a more complex mechanism driving the distinct host-pathogen interaction of S. Gallinarum/Pullorum with chickens than differential inactivation of a few genes.

Supplemental magnolol or honokiol attenuates adverse effects in broilers infected with Salmonella pullorum by modulating mucosal gene expression and the gut microbiota

“…Diseases caused by S. pullorum in chickens, known as pullorum disease, pose a great threat to the poultry industry, mainly in developing countries [ 13 , 14 ]. Salmonella infections resulting in compromised production performances, intestinal damage, and acute systemic diseases in broiler chickens have been widely reported [ 5 , 15 ].…”

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

“…S. Gallinarum 287/91, a spontaneous nalidixic acid-resistant strain [ 1 ], and Salmonella enterica serovar Typhimurium ( S. Typhimurium) SL1344 were grown in heart infusion broth (HIB) (Eiken Chemical, Tokyo, Japan) at 37°C with shaking (at 150 rpm). For experimental infection in chickens, the strains were cultured at 37°C in HIB to logarithmic phase, and then collected by centrifugation and washed twice with sterile 0.01 M phosphate-buffered saline (PBS).…”

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

“…The clinical signs were scored as 0 for being normal, 1 for being depression and ruffled feathers, 2 for depression, ruffled feathers, respiratory distress and 3 for the above mentioned clinical signs plus anorexia, emaciation and green-yellowish diarrhea, and 4 for death. When birds showed the clinical score of 3 (humane endpoint), the chickens were humanely sacrificed by cervical dislocation performed by trained veterinarians immediately [ 28 ]. Despite our efforts, some of the chickens used in the present study died before euthanasia (natural death by fowl typhoid).…”