Abstract
Aims
Prosthetic joint infection (PJI) remains the most severe complication of arthroplasty. Failure of intensive, long-term antibiotic treatment for PJI often requires removal of the implant. Antibiotic failure is thought to be caused by biofilm and persister formation. Novel anti-biofilm and anti-persister strategies are urgently needed. Here, we investigated the effects of several antimicrobial peptides on the bacteria within antibiotic-treated biofilms in an in vitro mature biofilm model on abiotic surfaces.
Methods
On polystyrene, a mature (7 day-old) methicillin-resistant Staphylococcus aureus (MRSA) biofilm was developed. Thereafter, bacteria in the biofilm were exposed to rifampicin and ciprofloxacin (both 10× >MIC) for three days. Surviving bacteria in the antibiotic-treated biofilm, presumed to include persisters, were exposed to increasing doses of the antimicrobial peptides SAAP-148, acyldepsipeptide 4 (ADEP4), LL-37 and pexiganan. SAAP-148 was further tested on antibiotic-treated mature biofilms on titanium/aluminium/niobium (TAN) discs and prosthetic joint liners.
Results
Daily exposure of the mature biofilm for seven days with antibiotics resulted in a 4-log reduction of MRSA without elimination of the bacteria. The surviving bacteria within the biofilm were eliminated upon subsequent exposure to SAAP-148 and pexiganan but not with LL-37 ad ADEP4. Antibiotic treatment of mature biofilms on TAN discs followed by SAAP-148 also resulted in eradication of bacteria within the biofilm. SAAP-148 also fully eliminated bacteria within antibiotic-treated mature MRSA biofilms on an ex vivo liner of a prosthetic joint.
Conclusions
A novel mature biofilm model has been developed in which the efficacy of antimicrobial peptides against bacteria, including persisters, residing within a biofilm was investigated. SAAP-148 and pexiganan were highly effective against the bacteria residing in antibiotic-exposed mature MRSA biofilms. This in vitro model system will be used to analyze the effects of novel antibiotic strategies and other anti-PJI agents.
