Technical guidance Update of the criteria used in the assessment of bacterial resistance to antibiotics of human or veterinary importance Prepared by the Panel on Additives and Products or Substances used in Animal Feed

The emergence and the spread of resistance to antimicrobials in bacteria pose a threat to human and animal health and present a major financial cost. In an effort to decrease the development of resistance various actions have been taken at Community level, including the removal of all antibiotics used for growth promotion purposes from animal feed in 2006. With this objective, the Scientific Committee on Animal Nutrition (SCAN) adopted an opinion in July 2001 defining the criteria used to assess the presence or absence of resistance determinants to antibiotics in microbial feed additives. As part of the self-tasking activities, the Panel on Additives and Products or substances used in Animal Feed (FEEDAP) identified the need to focus on this area and was requested to: i) revise the SCAN Opinion on the assessment of bacteria for resistance to antibiotics of human clinical or veterinary importance taking into consideration the data published after the adoption of the SCAN opinion, ii) define appropriate breakpoint values as indicative of the need for a more extensive assessment of the basis for resistance, and iii) consider whether the distinction between 'intrinsic' and 'acquired' resistance used as indicative of the probability of transfer of resistance is still valid for the safety assessment of microbial feed additives. Resistance to a given antimicrobial can be inherent to a bacterial species or genus ( intrinsic or natural resistance), or acquired through gain of exogenous DNA or by mutation of indigenous genes. For the purpose of distinguishing strains harbouring acquired antimicrobial resistance from susceptible strains, the FEEDAP Panel defines new microbiological breakpoints (also named epidemiological breakpoints) for ten (+ five for E. coli) antimicrobials which were chosen to maximise the identification of resistance genotypes to the most commonly used antimicrobials. The data used for the definition of microbiological breakpoints were derived from the published body of research and from national and European monitoring programmes. The determination of the MIC (minimum inhibitory concentration) above the breakpoint levels, identified by the FEEDAP Panel for one or more antimicrobials, requires further investigations to make the distinction between acquired and intrinsic resistance. Where resistance has been acquired by a strain belonging to a taxonomic group naturally susceptible to an antimicrobial, the degree of risk of transfer is generally considered to be substantially greater than that associated with intrinsic resistance. The FEEDAP Panel considers that strains of bacteria carrying an acquired resistance to antimicrobial(s) should not be used as feed additives, unless it can be demonstrated that it is a result of chromosomal mutation(s).