Specific bacterial commensals demonstrating multidrug resistance (MDR) are opportunistic pathogens for immunocompromised patients, including Corynebacterium species (spp.). Severe infections due to MDR corynebacteria are being increasingly reported where several MDR phenotypes have been described. One such phenotype, the macrolide-lincosamide-streptogramin B phenotype (MLSB), is characterized by high-level resistance to macrolides, lincosamides, and streptogramin B. Resistance is thought to be attributable to acquisition of the ermX gene, a methyltransferase that alters the ribosomal macrolide binding site. Until recently, ermX had been reported in only six Corynebacterium spp. We have observed other corynebacteria can also display high-level resistance to MLSB antimicrobials and are ermX positive. Hypotheses being tested include: 1) high-level macrolide and lincosamide resistance in Corynebacterium spp. is caused by acquiring ermX; 2) distribution of ermX is more widespread than previously published; 3) ermX is associated with transposon Tn5432; 4) multidrug resistance has spread to Canadian C. afermentans and C. aurimucosum strains.