Multicentre evaluation of a selective isolation protocol for detection of mcr-positive E. coli and Salmonella spp. in food-producing animals and meat

This study was conducted to evaluate the performance of a screening protocol to detect and isolate mcr-positive Escherichia coli and Salmonella spp. from animal caecal content and meat samples. We used a multicentre approach involving 12 laboratories from nine European countries. All participants applied the same methodology combining a multiplex PCR performed on DNA extracted from a pre-enrichment step, followed by a selective culture step on three commercially available chromogenic agar plates. The test panel was composed of two negative samples and four samples artificially contaminated with E. celi and Salmonella spp. respectively harbouring mcr1 or nicr-3 and mcr-4 or mcr-5 genes. PCR screening resulted in a specificity of 100% and a sensitivity of 83%. Sensitivity of each agar medium to detect mcr-positive colistin-resistant E. coli or Salmonella spp. strains was 86% for CHROMID (R) Colistin R, 75% for CHROMagar (TM) COL-APSE and 70% for COLISTIGRAM. This combined method was effective to detect and isolate most of the E. coli or Salmonella spp. strains harbouring different mcr genes from food-producing animals and hood products and might thus be used as a harmonized protocol for the screening of mcr genes in food-producing animals and food products in Europe.

Automated summary

This study evaluated the performance of a screening protocol to detect and isolate mcr-positive Escherichia coli and Salmonella spp. from animal caecal content and meat samples. The results showed that the combined method was effective in detecting and isolating E. coli or Salmonella spp. strains harboring different mcr genes, and could potentially be used as a harmonized protocol for screening mcr genes in food-producing animals and food products in Europe.