How do fluorescence spectroscopy and multimodal fluorescence imaging help to dissect the enhanced efficiency of the vancomycin-rifampin combination against Staphylococcus aureus infections?

Aptamer-Targeted Drug Delivery for Staphylococcus aureus Biofilm

Treatment of Staphylococcus aureus biofilm infections using conventional antibiotic therapy is challenging as only doses that are sublethal to the biofilm can be administered safely to patients. A potential solution to this challenge is targeted drug delivery. In this study, we tailored an aptamer-targeted liposomal drug delivery system for accumulation and delivery of antibiotics locally in S. aureus biofilm. In our search for a suitable targeting ligand, we identified six DNA aptamers that bound to S. aureus cells in biofilms, and we demonstrated that one of these aptamers could facilitate accumulation of liposomes around S. aureus cells inside the biofilm. Aptamer-targeted liposomes encapsulating a combination of vancomycin and rifampicin were able to eradicate S. aureus biofilm upon 24 h of treatment in vitro. Our results point to that aptamer-targeted drug delivery of antibiotics is a potential new strategy for treatment of S. aureus biofilm infections.

Synergistic Potential of Antimicrobial Combinations Against Methicillin-Resistant Staphylococcus aureus

The chemotherapeutic options for methicillin-resistant Staphylococcus aureus (MRSA) infections are limited. Due to the multiple resistant MRSA, therapeutic failure has occurred frequently, even using antibiotics belonging to different categories in clinical scenarios, very recently. This study aimed to investigate the interactions between 11 antibiotics representing different mechanisms of action against MRSA strains and provide therapeutic strategies for clinical infections. Susceptibilities for MRSA strains were determined by broth microdilution or agar dilution according to CLSI guideline. By grouping with each other, a total of 55 combinations were evaluated. The potential synergism was detected through drug interaction assays and further investigated for time-killing curves and an in vivo neutropenic mouse infection model. A total of six combinations (vancomycin with rifampicin, vancomycin with oxacillin, levofloxacin with oxacillin, gentamycin with oxacillin, clindamycin with oxacillin, and clindamycin with levofloxacin) showed synergistic activity against the MRSA ATCC 43300 strain. However, antibacterial activity against clinical isolate #161402 was only observed when vancomycin combined with oxacillin or rifampicin in time-killing assays. Next, therapeutic effectiveness of vancomycin/oxacillin and vancomycin/rifampicin was verified by an in vivo mouse infection model inoculated with #161402. Further investigations on antimicrobial synergism of vancomycin plus oxacillin and vancomycin plus rifampicin against 113 wild-type MRSA strains were evidenced by combined antibiotic MICs and bacterial growth inhibition and in vitro dynamic killing profiles. In summary, vancomycin/rifampicin and vancomycin/oxacillin are the most potential combinations for clinical MRSA infection upon both in vitro and in vivo tests. Other synergetic combinations of levofloxacin/oxacillin, gentamycin/oxacillin, clindamycin/oxacillin, and clindamycin/fosfomycin are also selected but may need more assessment for further application.