Effect of vancomycin-loaded microbubbles combined with ultrasound targeted microbubble destruction technology on methicillin-resistant Staphylococcus aureus biofilms / 中华创伤杂志

ABSTRACT

Objective:To investigate the effect of vancomycin (Vm)-loaded microbubbles (MBs) combined with ultrasound targeted microbubble destruction (UTMD) technique on the morphological structure, thickness and bacterial viability of methicillin-resistant Staphylococcus aureus (MRSA) biofilms.Methods:Vm-MBs were prepared by thin film hydration. Sterile coverslips in a diameter of 13 mm were placed in 24-well plates to construct in vitro biofilm models using MRSA as the test strain, and the biofilm morphology was observed by naked eye and light microscopy after crystal violet staining. LIVE/DEAD, SYTO59 and DIL were used to stain biofilms and MBs, respectively. After staining, the biofilm morphology and position of the biofilm in relation to MBs were observed using laser confocal scanning microscopy. The biofilms were divided into control group, Vm group, Vm-MBs group, UTMD group and Vm-MBs+UTMD group according to the random number table method, with 9 samples in each group. After biofilms of each group were treated accordingly for 24 hours, the morphological and structural changes of biofilms in each group were observed using laser confocal scanning microscopy and scanning electron microscopy following LIVE/DEAD staining; the difference in biofilm density in each group was measured with the aid of an enzyme marker following crystal violet staining; the difference in biofilm thickness and bacterial viability in each group were observed by laser confocal scanning microscopy. Results:The prepared Vm-MBs met the experimental requirements. The constructed biofilm model observed by naked eye, light microscopy and laser confocal scanning microscopy showed that the biofilm structure was dense with a relatively uniform thickness of (13.8±0.2)nm, a small amount of dead bacteria inside the membrane and the percentage of live bacteria of (94.9±0.3)%. Laser confocal scanning microscopy showed that MBs could penetrate into deeper layers of biofilms. After the respective treatment was given to each group for 24 hours, Laser confocal scanning microscopy and scanning electron microscopy following LIVE/DEAD staining showed that the biofilm morphological structure was most significantly disrupted in Vm-MBs+UTMD group compared to control, Vm, Vm-MBs and UTMD groups. In Vm-MBs+UTMD group, a large number of dead bacteria was observed, with only a few scattered planktonic bacteria and irregular changes in cell membrane morphology. Crystal violet staining showed that the biofilm density was significantly lower in Vm-MBs+UTMD group compared to control group ( P<0.05), while the differences between Vm, Vm-MBs and UTMD groups were not statistically significant (all P>0.05). Laser confocal microscopy showed that the biofilm thickness was thinner in Vm-MBs, UTMD and Vm-MBs+UTMD groups compared to control group (all P<0.05), with no significant difference between Vm group and control group ( P>0.05) and that the biofilm thickness was thinner in Vm-MBs+UTMD group compared to Vm, Vm-MBs and UTMD groups (all P<0.01), with no significant differences between the other groups (all P>0.05). Bacterial activity in Vm, Vm-MBs, UTMD and Vm-MBs+UTMD groups was significantly lower than that in control group (all P<0.01), with lower in Vm-MBs+UTMD group compared to Vm, Vm-MBs and UTMD groups (all P<0.01), but without significant difference between the other groups (all P>0.05). Conclusion:Vm-MBs combined with UTMD technology can effectively destroy the biofilm morphological structure to reduce biofilm thickness. Meanwhile, Vm-MBs combined with UTMD technology can release antibiotics and significantly decrease bacterial viability to improve antibiotic bactericidal efficacy.