In vitro and in vivo studies indicate that the dual combination of amoxicillin/cefdinir demonstrates a synergistic bactericidal efficacy against MRSA strains of various STs. Further research is needed to explore its potential as a treatment option for MRSA infections.

Fourteen representative prevalent MRSA strains with diverse sequence types (STs) were tested with a combination of amoxicillin and cefdinir, using chequerboard and time-kill assays. The Galleria mellonella larvae infection model was used to evaluate the in vivo efficacy of this dual combination against the community-acquired MRSA (CA-MRSA) strain USA300 and the hospital-acquired MRSA (HA-MRSA) strain COL.

The chequerboard assay revealed a synergistic activity of the dual amoxicillin/cefdinir combination against all tested MRSA strains, with fractional inhibitory concentration index (FICI) values below 0.5 and at least a 4-fold reduction in the MICs of both antibiotics. Time-kill assays demonstrated synergistic bactericidal activity of this dual combination against the MRSA strain USA300 and strain COL. Moreover, in vivo studies showed that the administration of amoxicillin/cefdinir combination to G. mellonella larvae infected with MRSA strains significantly improved the survival rate up to 82%, which was comparable to the efficacy of vancomycin. Conclusions: In vitro and in vivo studies indicate that the dual combination of amoxicillin/cefdinir demonstrates a synergistic bactericidal efficacy against MRSA strains of various STs. Further research is needed to explore its potential as a treatment option for MRSA infections.