Abstract
Biofilms are associated with chronic infection and frequently require surgical intervention even after prolonged antibiotic therapy. Bactericidal antibiotics are often ineffective at eradicating genetically susceptible cells within a biofilm because: 1) most conventional antibiotics target ATP-dependent processes and so work poorly on metabolically indolent persister cells within a biofilm; and 2) the biofilm matrix can act as a physical barrier to drug diffusion of certain classes of antibiotics. Antibiotic therapy that fails to completely eradicate the pathogen leads to chronic and relapsing infections, major financial healthcare burdens and significant mortality. Numerous approaches have been taken to improve biofilm killing but these often fail to achieve eradication. We address this problem with a novel two-pronged strategy with the aim of eradicating biofilm infection using 1) antibiotics which target persister cells as well as 2) improving drug penetration using ultrasound-stimulated phase-change contrast agents (US-PCCA).
We previously demonstrated that rhamnolipids, biosurfactant molecules produced by Pseudomonas aeruginosa, significantly potentiated aminoglycoside efficacy against S. aureus biofilm. We have also shown that US-PCCA can transiently disrupt biological barriers to therapeutic macromolecules. We hypothesized that combining antibiotics which target persister cells with US-PCCA to improve drug penetration could eradicate methicillin resistant S. aureus (MRSA) biofilms. To investigate this, we treated MRSA biofilms with a range of conventional and anti-persister antibiotics and/or US-PCCA. We found that vancomycin was significantly potentiated by US-PCCA, but a fraction of cells remained viable after the combination treatment. Aminoglycosides alone or in combination with US-PCCA displayed limited efficacy against MRSA biofilms. In contrast, the anti-persister combination of rhamnolipids and aminoglycosides combined with US-PCCA dramatically reduced biofilm viability, frequently culminating in complete eradication of the biofilm. These data demonstrate that biofilm eradication can be achieved using a combined approach improving drug penetration and therapeutics that target persister cells.
Competing Interest Statement
P.A.D declares that he is a co-inventor on a patent describing the formulation of low boiling-point perfluorocarbon agents and a cofounder of Triangle Biotechnology, a company that has licensed this patent. Additionally, P.G.D, P.A.D., B.P.C., V.P. and S.E.R. are all co-inventors on a provisional patent describing the use of low boiling-point phase change contrast agents for enhancing the delivery of therapeutics agents to biofilms. Additionally, B.P.C and S.E.R are co-inventors on a provisional patent describing the use of rhamnolipids for potentiating antibiotic efficacy. A.E.S declares that she has no competing interests.
