Influence of ultrasound-targeted microbubble destruction on biofilm

Abstract

Objective To investigate whether ultrasound (US)-targeted microbubble (MB) destruction (UTMD) can influence the biofilm and bacteria in morphology.Methods Twenty-hour biofilms of Staphylococcus epidermidis RP62A were treated with US or UTMD.The acoustic intensity was 0.5-1.5W/cm2,the duty cycle was 50％ and the duration was 10 minutes.After treatment,the absorbance values (A570) of biofilms stained with the crystal violet were measured to assess the biofilm density.The biofilms were observed with macroscopy and light microscopy.The biofilms were examined by confocal laserscanning microscopy (CLSM) and scanning electron microscopy (SEM).Results A thick and compact biofilm was observed in the untreated control group,and there were no obvious micropores in biofilms under macrology and light micrology.Although there were no significant changes under macroscopy in both biofilms treated with US only and UTMD with 0.5 W/cm2 acoustic intensity,interestingly,many micropores could be found under microscopy.The diameters of micropores increased with increasing acoustic intensity,and the micropores in biofilms treated with UTMD were bigger than those treated with US-only in the same condition of acoustic intensity (P ＜0.05).The largest diameters of micropores were up to 1 mm in biofilms treated with UTMD using 1.5 W/cm2 (P ＜0.05).The biofilm density (A570 value) decreased with increasing of the acoustic intensity,and the values in UTMD group of 1.5 W/cm2 were the lowest (P ＜ 0.05).Micropores also could be observed under CLSM.There were no obvious dead bacteria in biofilms treated with US and UTMD compared with untreated control group (P ＞0.05).Under SEM,the shape of bacteria in biofilms treated with US and UTMD became irregular,and many rounded projection could be observed in the surface of the bacteria treated with UTMD.Conclusions US and UTMD can produce micropores in biofilms,which might help to promote antibiotic activity against biofilms Key words: Ultrasonography; Microbubbles; Biofilms; Targeted therapy