Bacteriophage Sb-1 enhances antibiotic activity against biofilm, degrades exopolysaccharide matrix and targets persisters of Staphylococcus aureus

Most antibiotics have limited or no activity against bacterial biofilms, whereas bacteriophages can eradicate biofilms. We evaluated whether Staphylococcus aureus - specific bacteriophage Sb-1 could eradicate biofilm, both alone and in combination with different classes of antibiotics, degrade the extracellular matrix and target persister cells. Biofilm of methicillin-resistant S. aureus (MRSA) ATCC 43300 was treated with Sb-1 alone or in (simultaneous or staggered) combination with fosfomycin, rifampin, vancomycin, daptomycin or ciprofloxacin. The matrix was visualized by confocal fluorescent microscopy. Persister cells were treated with 10 4 and 10(7) plaque-forming units (PFU)/mL Sb-1 for 3 h in phosphate-buffered saline (PBS), followed by colony-forming units (CFU) counting. Alternatively, bacteria were washed and incubated in fresh brain heart infusion (BHI) medium and bacterial growth assessed after a further 24 h. Pretreatment with Sb-1 followed by the administration of subinhibitory concentrations of antibiotic caused a synergistic effect in eradicating MRSA biofilm. Sb-1 determined a dose-dependent reduction of matrix exopolysaccharide. Sb-1 at 10(7) PFU/mL showed direct killing activity on approximate to 5x10(5) CFU/mL persisters. However, even a lower titer had lytic activity when phage-treated persister cells were inoculated in fresh medium, reverting to a normal-growing phenotype. This study provides valuable data on the enhancing effect of Sb-1 on antibiotic efficacy, exhibiting specific antibiofilm features. Sb-1 can degrade the MRSA polysaccharide matrix and target persister cells and is therefore suitable for treatment of biofilm-associated infections. (c) 2018 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.