Brazilian researchers are investigating which genes are important for the survival of Salmonella to help prevent foodborne infections in humans.

The team from the School of Agricultural and Veterinary Sciences at the State University of São Paulo (FCAV-UNESP) are looking at survival of the bacterial species Salmonella in the intestinal tract of poultry.

Salmonella is able to use the inflammatory process it provokes as a source of energy to survive and multiply inside the gut. This is associated with the use of tetrathionate (ttr) as a by-product of the host inflammatory gut response. After production of ttr, it becomes possible to use propanediol (pdu) as an energy source.

Angelo Berchieri Junior, a professor at FCAV-UNESP. Photo by André Julião

Angelo Berchieri Junior, a professor at FCAV-UNESP, is responsible for a São Paulo Research Foundation (FAPESP) funded a project that will test the effects of deleting ttrA and pduA genes from Salmonella Enteritidis, Salmonella Typhimurium, and Salmonella Heidelberg.

The work, which started last year and continues until mid-2023, was presented at FAPESP Week London in February. The symposium aimed to strengthen links between researchers from Brazil and the United Kingdom as part of the UK-Brazil Year of Science and Innovation 2018-2019.

Berchieri said Salmonella easily colonizes the digestive tract of poultry and may or may not cause disease.

“Even when they do not affect the chickens themselves, they are able to infect humans who eat the chicken. We selected these three serotypes because they are frequently found in poultry and may cause foodborne infections in humans.”

Presence of certain serotypes in Brazilian poultry has caused Europe to block containers exported by Brazil. Some meat plants were banned last year from selling to the European Union following an EU audit. Police in Brazil investigated the sector in 2017 and alleged some health inspectors had been bribed so meat produced in unhygienic conditions could be sold.

Salmonella Heidelberg is the least common among humans of the three types being studied. However, it is widespread in Brazil and could compromise exports as it was found in Brazilian poultry shipments not accepted in Europe.

Brazilian law restricts Salmonella Enteritidis and Typhimurium. However, depending on the country of import, other serotypes of Salmonella in exported poultry may also be subject to restrictions. Earlier this month, BRF S.A. recalled more than 450 tons of fresh chicken due to potential Salmonella Enteritidis contamination.

Also part of the project is Mauro de Mesquita Souza Saraiva and biologist Gabriele Tostes Gricio.

The aim is to better understand the relationship between bacteria and host, contributing to more knowledge of bacterial behavior and alternatives to inhibit intestinal survival and colonization.

Researchers infected one group of chicks with a wild type bacterium without genetic modification and the other group with Salmonella whose ttrA or pduA genes had been deleted to determine which genes cause the bacteria to become resistant to the immune system of poultry.

They then compared the two groups for the presence of bacteria in feces, the cecum – which is a pouch that forms the first part of the large intestine – the liver and spleen.

By identifying the genes that allow the bacteria to survive, researchers are able to generate mutant forms that may be used as a vaccine.

When the immune system comes into contact with a variety that does not kill the animal but survives for a period of time, that animal establishes an immunological memory. If it is later exposed to a harmful version of the bacteria its defenses will be ready to attack it.

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