The use of antimicrobial growth promoters has caused the development of resistance in a number of important pathogenic bacterial species. Furthermore, most cases in which antimicrobials belonging to one single class of antibiotics have been used as therapeutic drugs for both humans and animals have resulted in the development of cross resistance to these drugs. Some of the bacteria developing resistance are pathogenic to animals or man, and the development of resistance to growth promoters and related therapeutic drugs has limited the therapeutic options for these bacteria. In the case of E. faecium, resistance has developed towards very important "last resort" antimicrobials. Although the full public health consequences of the development of resistance through the use of antimicrobial growth promoters have not yet been determined, there is nevertheless a need to take precautionary actions in order to prevent further development of resistance towards a number of antimicrobials used as growth promoters.