Enhanced antimicrobial effect of gentamicin against Escherichia coli through microbubble-mediated ultrasonic techniques

Abstract

Objective To investigate effect of microbubble-mediated ultrasonic techniques on activity of gentamicin against E.coli,as well as the possible mechanism.Methods The planktonic E.coli were divided into control group,ultrasound group,microbubble group and microbubble-ultrasound group.There were 3 different concentrations of gentamicin (0,1,2 μg/ml) in each group.The concentration of the microbubbles was 10％ (v/v).The parameters of ultrasound included irradiation intensity (300 mW/cm2),frequency (46.5 kHz),duty ratio (33％) and expose time (12 hours).Bacteria were cultured and detected by a semiquantitative plate assay.The numbers of CFU were calculated and statistically analyzed (log10 CFU/ml).Finally,the bacterial liquid was obtained and scanned by transmission electron microscope to observe the micromorphology structure of bacteria.Results In 0 μg/ml of gentamicin group,there was no statistical difference in amount of residual bacteria between 4 groups.In 1 μg/ml of gentamicin group,the number of residual bacteria in microbubble-ultrasound group (5.44±0.49 log10 CFU/ml) was significantly smaller than those in microbubble group (7.19±0.38 log10 CFU/ml),control group (7.44±0.64 log10 CFU/ml) and ultrasound group (6.86±0.29 log10 CFU/ml).In 2 μg/ml of gentamicin group,the number of residual bacteria in microbubble-ultrasound group (2.87±0.28 log10 CFU/ml) was still smaller than those in microbubble group (4.33±0.40 log10 CFU/rnl),control group (4.45±0.43 log10 CFU/ml) and ultrasound group (3.89±0.37 log10CFU/ml).The electron micrographs showed the bacterial cytoplasmic membrane was more folded and discontinuous in microbubble-ultrasound group.Conclusion Compared with the single ultrasound,the microbubble-mediated ultrasonic techniques can further enhance the antibacterial effect of gentamicin against E.coli,and its mechanism is likely to be associated with Sonoporation. Key words: Microbubbles; Ultrasonic therapy; Escherichia coli; Gentamicins; Infection