Codelivery of Methicillin and a TLR-9 Agonist Promotes Bacterial Clearance and Establishes Reinfection Protection in a Model of Methicillin-Resistant Staphylococcus aureus Renal Infection

Methicillin-resistant Staphylococcus aureus (MRSA) infections represent a significant clinical challenge, with high rates of β-lactam resistance and reinfection. Here, we report a combination therapy combining methicillin with a Toll-like receptor 9 (TLR9) agonist (CpG-ODN M362) delivered via a subcutaneously injectable hyaluronic acid - methylcellulose (HAMC) hydrogel for the treatment of MRSA kidney infections. In a murine renal infection model, combination therapy achieved logarithmic reductions in renal bacterial burden compared to either monotherapy, while also preserving protective immune memory that methicillin alone failed to generate. Formulation within a thermosensitive, shear-thinning HAMC hydrogel enabled sustained codelivery of both agents from a single subcutaneous injection, enhancing bacterial clearance and humoral immune responses compared to daily bolus administration. This work demonstrates that hydrogel-mediated immunostimulatory combination therapy represents a promising single-dose strategy for treating MRSA infection with otherwise ineffective antibiotics while simultaneously guarding against reinfection.