Abstract
Aim
Irrigation is a major step during debridement surgery in the context of Prosthetic Joint Infections (PJI), but its effects on biofilms are poorly described.
The present study aims at evaluating the effect of PW alone or followed by antibiotics on MSSA and MRSA biofilms grown on Ti6Al4V coupons in-vitro.
Method
Strains: 1 reference (MSSA: ATCC25923; MRSA: ATCC33591) and 2 clinical MSSA and MRSA isolated from PJI.
Biofilm culture: Coupons were incubated for 24h at 37°C with bacteria (starting inoculum ∼6.6Log10CFU/mL in TGN [TSB + 1% glucose + 2% NaCl]), under shaking at 50rpm.
Treatment: Half of the coupons were irrigated with 50mL physiological serum from 5cm using a Stryker Interpulse; the coupons were then either analysed (ControlT0 and PWT0) or reincubated for 24h in TGN or TGN containing flucloxacillin (MSSA) or vancomycin (MRSA) at MIC or 20mg/L.
Analysis: Coupons were rinsed twice with PBS. Biomass was measured by crystal violet (CV) assay. CFUs were counted after recovering bacteria from coupons using sonication and TSA plating.
Results
Antibiotics alone: Flucloxacillin reduced CFU and biomass for ATCC25923 and 611 but not 578 (Fig b and d). Vancomycin had no statistically significant effects on CFUs for all MRSA and only a weak effect on biomass for 676.
Irrigation alone markedly reduced CFUs and biomass for all strains but had no persistent effect after 24h reincubation in TGN.
PW + antibiotics: Antibiotics prevented bacterial regrowth after PW when used at their MIC and further decreased CFUs when used at 20 mg/L.
Conclusions
PW alone has a transient effect on coupon colonisation by S. aureus biofilms.
Vancomycin at therapeutic concentrations is ineffective and flucloxacillin has a strain-dependent effect.
In combination, these treatments show synergistic effects, indicating the importance of irrigation followed by high antibiotic doses for ODRI.
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