Use of antimicrobials and antimicrobial resistance in the poultry industry.

In the last decades, the emergence and spread of antimicrobial resistance has become one of the most serious health threat for animals and humans. Antimicrobial resistance may develop in pathogenic, commensal and environmental bacteria through several different mechanisms, depending on the antimicrobial agent and the bacterial species. Antimicrobial resistance is mediated by mutations of the bacterial target proteins and/or by mobile genetic elements (i.e. plasmids, integrons, or transposons) carrying resistance genes. Among these, the latter is considered to be the most worrisome since it leads to the horizontal transfer of resistance genes among bacteria. Although resistance to antimicrobials is a naturally occurring phenomenon, the antimicrobial usage in animal and human medicine may create selective pressure inducing the dissemination of resistance at a very rapid rate within bacterial populations. Antimicrobial agents have ever been used in poultry production to control infectious diseases, as well as to promote growth. In the last years, however, the emergence and spread of resistant bacteria have rendered many antimicrobials ineffective for poultry treatments. Additionally, several antimicrobials are being discontinued from use in poultry to protect public health, since they are also used in human medicine. Indeed, poultry is considered a source of resistance genes and bacteria, which can be transmitted to humans directly through the food production chain or indirectly through the environment. However, it is still unclear the extent to which antimicrobial use in poultry, emergence and spread of resistant bacteria along the food chain and resistant infections in humans are correlated. To control the dissemination of antimicrobial resistance and to preserve the effectiveness of antimicrobial agents for both animals and humans treatment, many programmes of antimicrobial stewardship in food animal production, including poultry, have been implemented worldwide. In the European Union (EU), for example, antimicrobial growth promoters in animal feed have been banned in 2006 and surveillance systems of antimicrobial use and resistance have been established in many countries. However, to minimize the threat of antimicrobial resistance it is fundamental that a One Health approach is promoted since humans, animals and the environment are all involved in the emergence and spread of antimicrobial resistance. This presentation will give a brief overview of the current issues related to antimicrobial use and resistance in the poultry industry. Given the complexity of the issue, resistance to some antimicrobials (e.g. cephalosporins, fluoroquinolones, macrolides, colistin) in selected bacterial species (e.g. Salmonella, Cam- pylobacter, Escherichia coli) will be presented. The molecular mechanisms involved in the emergence and spread of resistance, as well as the actions to undertake for monitoring and controlling resistance will be also mentioned.