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UCD Centre for Food Safety

Ionad Sábháilteachta Bia UCD

Antimicrobial resistance, efflux mechanisms and molecular typing of Salmonella spp

Salmonella can be isolated from numerous animal species and is known as a principal zoonotic bacterium causing symptoms such as diarrhea, fever and septicemia. These symptoms can be lethal to animals, so swift treatment with the appropriate antimicrobial agents is important. Non-typhoidal salmonellosis in humans is usually a self-limiting disease confined to the gastro-intestinal tract, but when infection spreads or when an immunocompromised individual is affected appropriate antimicrobial treatment is essential. There is a considerable amount of information on antimicrobial resistance in Salmonella of human and food animal origin. Many of these strains are simultaneously resistant to three or more classes of drug, and are termed multi-drug resistant (MDR). Antimicrobial drug use in food animals can promote the development of a MDR phenotype. This is accomplished through the acquisition of resistance genes by bacteria. Studies demonstrated that the genes associated with a MDR resistance phenotype of S. Typhimurium DT104 are chromosomally encoded and that they are part of a large genomic island.

The emergence of decreased susceptibility to flouroquinolones in MDR S, Typhimurium DT104 is increasing and it is associated with point mutations in the quinolone resistance determining region (QRDR) of a target gene, gyrA. Another important mechanism is the over expression of efflux pumps such as the acrAB-tolC. In addition there may be mutations in the regulatory genes of the marRAB operon which contribute to efflux overproduction and hence a MDR phenotype. There have also been reports of tranquilizers having a similar effect. Therefore increased resistance of Salmonella spp to antibiotics is not only due to mobile elements that carry resistance genes but also the activity of efflux pumps which can be influenced by many xenobiotic compounds. It is possible that both mechanisms could act synergistically to develop a MAR phenotype.

This project investigates the genetic basis for MDR in Salmonella.

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PCR gel