Guidance on the assessment of bacterial susceptibility to antimicrobials of human and veterinary importance

This Guidance document is intended to provide a method to identify resistance to antimicrobials of human and veterinary importance in bacterial strains intended for use as feed additives. Such tests should be made in a consistent manner using internationally recognised and standardised methods. As a basic requirement, the minimum inhibitory concentration of the antimicrobials should be determined for each of the following substances: ampicillin, vancomycin, gentamicin, kanamycin, streptomycin, erythromycin, clindamycin, tetracycline, chloramphenicol and, in specific cases, tylosine, apramycin, nalidixic acid, sulfonamide and trimethoprim. These antimicrobials are chosen to detect a wide range of determinants for resistance. The cut-off values identified by the FEEDAP Panel should be seen as a pragmatic response intended to introduce consistency in the separation of strains with acquired resistance from susceptible strains. These values are not intended for any purpose other than the assessment of microbial products for the possible presence of antimicrobial resistance. When a bacterial strain demonstrates higher resistance to a specific antimicrobial than the other strains of the same taxonomical unit, the presence of acquired resistance is indicated and additional information is needed on the genetic basis of the antimicrobial resistance. Any bacterial strain carrying an acquired resistance to antimicrobial that is shown to be due to the acquisition of genetic determinant presents the greatest potential for horizontal spread and should not be used as a feed additive.