Pleuromutilin was discovered in 1951 from an edible mushroom, Pleurotus mutilus, but it was not until the early 1970s that its potential for use as an antimicrobial was more fully recognized (2). Tiamulin and valnemulin were developed as semisynthetic pleuromutilins whose antimicrobial activity was traced to inhibition of bacterial protein synthesis following interaction with the peptidyltransf...