Detection of Salmonella Heidelberg resistant to colistin in the intestinal content of pigs at slaughter

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Werlang, Gabriela
Paim, Daniel
Vieira, Tatiana
Pissetti, Caroline
Kich, Jalusa
Cardoso, Marisa
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International Conference on the Epidemiology and Control of Biological, Chemical and Physical Hazards in Pigs and Pork
Iowa State University Conferences and Symposia

The SafePork conference series began in 1996 to bring together international researchers, industry, and government agencies to discuss current Salmonella research and identify research needs pertaining to both pig and pork production. In subsequent years topics of research presented at these conferences expanded to include other chemical and biological hazards to pig and pork production.


Salmonella Heidelberg has increasingly been reported as cause of human salmonellosis worldwide. In Brazil, S. Heidelberg has been reported in poultry but it is infrequently isolated from pigs. Here, we describe the isolation of S. Heidelberg resistant to colistin from slaughter pigs. Five pigs and their carcasses belonging to a same slaughter batch in ten consecutive days were sampled for fragment of intestine in the ileocecal region and sponges rubbed on the carcass surface (400 cm2) before chilling. Salmonella detection was performed according to the ISO 6579:2002. Intestinal content was also subjected to Salmonella enumeration by a miniaturized Most Probable Number (MPN) protocol. Salmonella isolates were characterized by antimicrobial resistance by the disk diffusion test, the minimum inhibitory concentration to colistin determination and to gene mcr-1 investigation by PCR. Salmonella was isolated from the intestinal content of 64% (32/50) of the pigs, in amounts that varied from 2.7 to >1,400 MPN/g. Salmonella Heidelberg was the most frequent serovar identified in the intestinal content samples (20/50; 40%), and this serovar was present in eight of the ten pig batches sampled. At the prechill, Salmonella was isolated from 8% of carcasses, and S. Heidelberg was not detected. Salmonella Heidelberg strains were resistant against ampicillin (n=9), tetracycline (n=8), sulfonamide (n=8) and gentamicin (n=5). Nine multi-drug resistant strains were detected; among them four strains were positive for the gene mcr-1. In these strains the MIC value was 8 μg.mL-1, while in the strains without the mcr-1 gene it ranged from 2 μg.mL-1 to 4 μg.mL-1. Therefore, humans in contact with carrier pigs or their environment may be exposed to S. Heidelberg, including strains harboring the gene mcr-1.

Sun Jan 01 00:00:00 UTC 2017