Resistance to tetracycline was studied in Salmonella Infantis isolated from 28 poultry farms in the Northern part of Serbia (The Autonomous Province of Vojvodina). A total of 18 isolates were resistant to nalidixic acid (NAL) and tetracycline (TET). The minimal inhibitory concentration (MIC) to TET, ranged from 1-256 mg/L. Namely, 13 isolates exhibited MIC to TET at 256 mg/L, in four of the isolates, the MIC was 128 mg/L and one isolate had MIC 64 mg/L. Ten isolates were exhibiting a MIC of 1mg/L. It was evident that Salmonella Infantis had also spread to breeders and layers. In this work, we detected the tetA gene and the corresponding tetR gene (encoding the repressor protein) as well as the truncated transposon Tn1721, which are responsible for the resistance to TET. The presence of the non conjugative transposons from the conjugative plasmid has facilitated the spread of resistance to TET in Salmonella. It was concluded that higher biosecurity practice in poultry farming presents the best option to eliminate infections caused by Salmonella spp. from poultry flocks in Serbia. A rational use of antimicrobials is necessary to prevent any further spread of Salmonella Infantis resistant clones.
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