No abstract

In the natural environment, bacteria most often live in communities bound to one another by secreted adhesives. These communities, or biofilms, play a central role in biogeochemical cycling, microbiome functioning, wastewater treatment, and disease. Wherever there are bacteria, there are also viruses that attack them, called phages. Interactions between bacteria and phages are likely to occur ubiquitously in biofilms. We show here, using simulations and experiments, that biofilms will in most conditions allow phage-susceptible bacteria to be protected from phage exposure, if they are growing alongside other cells that are phage resistant. This result has implications for the fundamental ecology of phage-bacteria interactions, as well as the development of phage-based antimicrobial therapeutics.

Bacteriophages can be trapped in the matrix of bacterial biofilms, such that the cells inside them are protected. It is not known whether these phages are still infectious and whether they pose a threat to newly arriving bacteria. Here we address these questions using Escherichia coli and its lytic phage T7. Prior work has demonstrated that T7 phages are bound in the outermost curli polymer layers of the E. coli biofilm matrix. We show that these phages do remain viable and can kill colonizing cells that are T7-susceptible. If cells colonize a resident biofilm before phages do, we find that they can still be killed by phage exposure if it occurs soon thereafter. However, if colonizing cells are present on the biofilm long enough before phage exposure, they gain phage protection via envelopment within curli-producing clusters of the resident biofilm cells.

No abstract

In orthopaedic trauma surgery, biofilms account for up to 65% of all infections, typically showing increased resistance to antibiotics, and thus novel anti-biofilm approaches need to be developed. Antimicrobial photodynamic therapy (PDT) had been recently proposed to combat clinically relevant biofilms using photosensitizers to kill bacteria with light-induced reactive oxygen species. In the first stage of the study reported here, we assessed the efficacy of this treatment type in eradication of biofilms typically present on surfaces of orthopaedic devices (e.g., intramedullary nails and osseointegrated prosthetic implants) by growing them in vitro inside soft lithography-fabricated microfluidic chips, treating them with 5- Aminolevulinic acid-based PDT and evaluating treatment efficacy with optical coherence tomography. PDT outcomes were compared to biofilm response to clinical antibiotic treatment (Vancomycin/Tobramycin 1:1 mixture). The antibacterial efficiency of 5-Aminolevulinic acid (5-ALA)-based PDT was found to be nonlinear dependent on the photosensitizer concentration and the light power density, with lowest parameters still being 17 times more effective than antibiotic-treated groups, reaching 99.98% bacteria kill at 250 mW/cm2 light power density, 100 mg/mL 5-ALA concentration setting. Performed experiments enable the translation of the developed portable treatment/imaging platform to the second phase of the study: PDT treatment response assessment of biofilms naturally grown on orthopaedic devices of clinical patients.