The postantibiotic effect-like effect of photothermal agents: evidence from IR780 nanoparticles and indocyanine green

Introduction Postantibiotic effect (PAE) refers to the temporary suppression of bacterial growth after transient antimicrobial treatment. In recent years, due to the spread of antibiotic resistance, photothermal agents (PTAs) have been broadly studied for infection treatments. However, the PAE-like effect of PTAs has not been investigated. Methods This study focuses on the PAE-like effect of representative PTAs, namely IR780 nanoparticles (NPs) and indocyanine green (ICG), against MRSA and a CRE isolate. The effects of PTA type, bacterial species, PTA concentration, and near-infrared irradiation duration on the PAE-like effect were systematically evaluated. Results Results showed that the PAE-like effect of these PTAs against MRSA and a CRE isolate was evident. Further experiments showed that the PAE-like effect was affected by PTA type, bacterial species, PTA concentration, and near-infrared irradiation duration. Furthermore, the PAE-like effect of IR780 NPs was enhanced by 34.6% when a targeting group was conjugated to its nanostructure. Discussion The mechanism of the PAE-like effect of PTAs against MRSA is suggested to be related to thermally induced damage. Overall, this work provides the first evidence of a PAE-like effect in PTAs against MRSA, which may provide a preliminary basis for future optimization of photothermal therapy regimens against resistant infections.