Pan-European monitoring of susceptibility to human-use antimicrobial agents in enteric bacteria isolated from healthy food-producing animals

Objectives: To determine the antimicrobial susceptibility of Escherichia coli, Salmonella, Campylobacter and Enterococcus from cattle, pigs and chickens across the European Union (EU) using uniform methodology. Methods:Intestinal samples (1624) were taken at slaughter across five EU countries. Bacteria were isolated in national laboratories, whilst MICs were determined in a central laboratory for key antimicrobials used in human medicine. Clinical resistance was based on CLSI breakpoints and decreased susceptibility based on European Food Safety Authority (EFSA)/EUCAST epidemiological cut-off values. Results:Isolation rates were high for E. coli (n1540), low for Salmonella (n201) and intermediate for Campylobacter (n940) and Enterococcus (n786). For E. coli and Salmonella, clinical resistance to newer compounds (cefepime, cefotaxime and ciprofloxacin) was absent or low, but decreased susceptibility was apparent, particularly in chicken strains. Resistance to older compounds (except gentamicin) was variable and higher. Colistin resistance was absent for E. coli, but apparent for Salmonella. For Campylobacter jejuni, ciprofloxacin resistance was markedly prevalent for chickens, whereas clinical resistance and decreased susceptibility to erythromycin was absent or very low. For Campylobacter coli, resistance was notably higher. None of the Enterococcus faecium strains was resistant to linezolid, but some were resistant to ampicillin or vancomycin. Resistance to quinupristin/dalfopristin was frequent. Conclusions:Resistance patterns varied widely depending on bacterial species, antibiotics, hosts and region. Resistance varied among countries, particularly for older antimicrobials, but clinical resistance to newer antibiotics used to treat foodborne disease in humans was generally very low. In the absence of resistance to newer compounds in E. coli and Salmonella, the apparent decreased susceptibility should be monitored.