Effects of low-intensity and low-frequency ultrasound combined with tobramycin on biofilms of Extended-Spectrum Beta-Lactamases (ESBLs) Escherichia coli.

Low-intensity and low-frequency ultrasound (LILFU) can enhance bactericidal action of antibiotics against various sensitive bacterial species. The present study investigated to clarify the effects of low-intensity and low-frequency ultrasound (LILFU) combined with tobramycin on ESBLs E.coli biofilm (a multi-drug resistant bacteria). The biofilms of ESBLs E. coli were established and treated with ultrasound (42 kHz and ISATA of 0.66 W/cm2) continuously for 0.5 h with and without tobramycin. The bacterial viability, the morphology and the antibiotic penetration of ESBLs E. Coli biofilms would be detected. The results demonstrated that the bacterial viability of biofilms was significantly declined and the diameter of the inhibition zone was significantly increased after treatment with ultrasound combined with tobramycin compared to the controls (P < 0.05). Confocal laser scanning microscope (CLSM) showed the bacterial viability was affected the most in the outer layer of ESBLs E. coli biofilms after the joint treatment. The morphological structure of the biofilms was altered remarkably after joint treatment based on scanning electron microscopy (SEM), especially in regard to reduced thickness and loosened structure. These results suggest that the combination of ultrasound and tobramycin can exert synergistic bactericidal effects against biofilms formed by ESBLs E. Coli.