Effect of mgtC gene deletion on Salmonella Gallinarum pathogenicity in susceptible poultry

Author(s)

Lucas Bocchini Rodrigues Alves

• Document type: Doctoral Thesis
• Press: Jaboticabal. 2022-07-25.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agrárias e Veterinárias. Jaboticabal
• Defense date: 2022-05-31
• Advisor: Angelo Berchieri Junior; Oliveiro Caetano de Freitas Neto

Abstract

Salmonella Gallinarum (SG) provokes the so-called Fowl Typhoid, an infectious disease of acute clinical course that affects gallinaceous of any age and leads to high mortality rates. During the typhoid-like systemic infection caused by Salmonella Typhimurium (STM) in mice, the bacterium expresses the mgtC gene, which is clustered in the Salmonella Pathogenecity Island – 3 (SPI-3). Its function is apparently linked to bacterial replication within macrophages and its absence attenuates the pathogen. In this sense, it was hypothesized that knocking-out mgtC from SG genome could alter the microorganism pathogenicity in susceptible commercial poultry taking into account the central role of systemic infection to the pathogen. Thus, the present study sought to elucidate the importance of mgtC on SG pathogenicity. For this, a mgtC-lacking Salmonella Gallinarum mutant was constructed (SG ∆mgtC). In addition, its ability to replicate in medium that mimicries the intracellular environment of macrophages and also in this immune cell types was evaluated. Moreover, the infection of susceptible chickens by SG ∆mgtC and the wild-type strain was performed to compare the pathogenicity, systemic infection and the elicited immune responses by measuring mRNA of IFN-γ and LITAF cytokines by RT-qPCR and the population of macrophages and lymphocytes T CD4+ and CD8+ by means of immunohistochemistry. It was observed herein that mgtC was required for Salmonella Gallinarum replication in both acidified low-Mg2+ media and macrophages. Nevertheless, lower bacterial counts was only noticed at the late stage of infection without affecting the citotoxicity. In vivo experiments showed that knocking-out the mgtC gene neither alters bacterial invasiveness ability nor affects bacterial counts in liver and spleen and total chicken mortality. However, plotting a survival curve and analysing the development of clinical-pathologic conditions, it was observed a slower progression of the disease in chickens infected by SG ∆mgtC compared to those challenged by the wild-type strain. Furthermore, it was required more 1.36 Log10 of CFU/mL of mutant strain to provoke 50 % of mortality in comparison to the wild-type strain. Moreover, the mRNA expression of IFN-γ and LITAF were similar between the infected chickens, but higher than those uninfected. The same was observed in macrophages and lymphocytes T CD4+ populations. On the other hand, the presence of lymphocytes T CD8+ was higher in the initial phase of the disease provoked by the wild-type. The role of mgtC in Fowl Typhoid in susceptible chickens differs from the typhoid-like infections in mammals, since its depletion attenuated other serovars. Thus, the deletion of mgtC gene from Salmonella Gallinarum genome does not affect the pathogenicity, but slightly alters the pathogenesis. (AU)

• FAPESP's process: 18/12614-7 - Effect of the mgtC gene-deletion on Salmonella gallinarum pathogenicity in susceptible poultry
• Grantee: Lucas Bocchini Rodrigues Alves
• Support Opportunities: Scholarships in Brazil - Doctorate