3.5 Drug resistance evaluation
Long-term overuse of antibiotics could easily induce drug resistance of bacteria. Thus, we further explored whether OHH NPs with laser assistance could reduce the occurrence of ofloxacin resistance. To evaluate the development of bacterial resistance with different treatments, K.pneumoniae was continuously cultured with a sublethal dose of ofloxacin (one-tenth of the concentration in Fig. 3A) or OHH NPs+NIR. As shown in Fig. 5E, the MIC value ofK.pneumoniae incubated with ofloxacin was 7 times that of initial MIC after 5 circles’ incubation, suggesting serious drug resistance. On the contrary, the MIC value ofK.pneumoniae after 5 circles’ treatment with OHH NPs+NIR was nearly same as the initial MIC. Due to the effective synergy of OHH NPs and PTT, OHH NPs showed excellent antibacterial ability with laser assistance. Therefore, OHH NPs combined with laser irradiation could effectively reduce the dosage of ofloxacin without compromising the bactericidal capability and delay the development of drug resistance, which could be considered as a long-term antibacterial strategy.