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

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 <i>Staphylococcus aureus</i> to the macrolide, lincosamide, streptogramin (MLS_B) class of antibiotics using antisense oligomers (ASOs). We designed and screened ASOs that target the <i>ermC</i> gene known to confer resistance to MLS_B antibiotics. A peptide nucleic acid designed to bind the ribosome binding site of the <i>ermC</i> mRNA and conjugated to a TAT cell penetrating peptide shows the highest efficiency of targeting <i>ermC</i> in <i>S. aureus</i> cells. This ASO enhances <i>S. aureus</i> sensitivity to certain MLS_B antibiotics without affecting susceptibility to mechanistically different antibiotics, indicating a high specificity for targeting <i>ermC</i>. Using in vitro binding and translation assays, we show that the ASO binds to the target mRNA region and decreases translation of the <i>ermC</i> 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 <i>ermC</i> mRNA are strictly conserved.