Antisense Oligomer Targeting the Antibiotic Resistance Gene ermC Augments Erythromycin, Azithromycin, and Virginiamycin Sensitivity in Staphylococcus aureus

Rising antimicrobial resistance has made certain antibiotics ineffective and threatens to make them obsolete. In this work, we seek to resensitize a macrolide-resistant strain of Staphylococcus aureus to the macrolide, lincosamide, streptogramin (MLSB) class of antibiotics using antisense oligomers (ASOs). We designed and screened ASOs that target the ermC gene known to confer resistance to MLSB antibiotics. A peptide nucleic acid designed to bind the ribosome binding site of the ermC mRNA and conjugated to a TAT cell penetrating peptide shows the highest efficiency of targeting ermC in S. aureus cells. This ASO enhances S. aureus sensitivity to certain MLSB antibiotics without affecting susceptibility to mechanistically different antibiotics, indicating a high specificity for targeting ermC. Using in vitro binding and translation assays, we show that the ASO binds to the target mRNA region and decreases translation of the ermC gene. The specific effect of the ASO is evident as a decrease in the methylation activity of the ErmC protein. Sequence comparisons reveal a subset of bacterial species where both the ErmC protein and the antisense target site on the ermC mRNA are strictly conserved.