Association of antimicrobial usage with faecal abundance of aph(3')-III, ermB, sul2 and tetW resistance genes in veal calves in three European countries

BACKGROUND: High antimicrobial use (AMU) and antimicrobial resistance (AMR) in veal calves remains a source of concern. As part of the EFFORT project, we determined the association between AMU and antimicrobial resistance genes (ARGs) abundance in veal calves in three European countries. METHODS: In 2015, we collected faecal samples of calves close to slaughter from farms located in France, Germany and the Netherlands (20 farms per country, 25 calves per farm). Standardized questionnaires were used to record AMU and farm characteristics. In total, 405 faecal samples were selected for DNA extraction and qPCR to quantify the abundance (16S normalized concentration) of four ARGs [aph(3')-III, ermB, sul2 and tetW] encoding for resistance to frequently used antimicrobials in calves. Multiple linear mixed models with random effects for country and farm were used to relate ARGs to AMU and farm characteristics. RESULTS: We found a significant positive association between trimethoprim/sulfonamide use and the concentration of sul2 in veal calves' faeces. A higher weight of calves at arrival was negatively associated with aph(3')-III and ermB. At farms with non-commercial animals present, we found lower aph(3')-III concentrations. Furthermore, farms using only water for cleaning of stables had a significantly lower faecal ermB and tetW abundance compared to other farms. CONCLUSION: A positive association was found between trimethoprim/sulfonamide use and sul2 abundance in veal calves. Additionally, other relevant risk factors associated with ARGs in veal calves were identified, e.g. weight at arrival at the farm and cleaning practices