The potential of phage K against Staphylococcus aureus biofilms was assessed. Biofilms were formed on stainless steel surfaces at 25 ºC for 24 h by two strong-biofilm producing strains isolated from food industry surfaces (IIM 222 and IIM 240) and the host strain DPC 5246. Biofilms were challenged with a multiplicity of infection (MOI) ranging from 0.03 to 30 during the subsequent 24 h at 25 ºC. Planktonic stationary-phase cells were also challenged with a MOI between 0.003-30 under identical conditions. Phage K was approximately 10-fold concentrated from original lysates by using polyethylene glycol 8000 in order to apply high MOIs. Planktonic cells of all strains were very susceptible to all MOIs tested, but complete removal was only detected for the host strain (at a MOI of 30). On the contrary, phage K had hardly effect at MOIs < 3 and was only highly effective to remove biofilms formed by two out of the three strains (DPC 5246 and IIM222) at MOIs ≥ 30. No cells were detected only in DPC 5246 biofilms by applying a MOI of 1000. Differences in dose-response patterns were not only accounted for by the susceptibility of strains to phage K or the number of cells forming biofilms, but also by biofilm architecture
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