Abstract
INTRODUCTION
Prosthetic joint related-infections (PJRI) are severe complications in orthopaedic surgery. Staphylococcus aureus and Staphylococcus epidermidis are the most commonly isolated pathogens from implants (1). The variable antimicrobial susceptibility found in these microorganisms, makes it necessary to perform individual susceptibility studies in order to select the best antibiotic combination for clinical management (2).
MATERIAL AND METHODS
35 staphylococcal strains (17 S. aureus, 18 S. epidermidis) were isolated from PJRI using a previously described sonication protocol (3). Biofilm-producing collection strains S. aureus 15981 (4) and S. epidermidis ATCC 35984 were also included in the study. In vitro susceptibility was evaluated against 7 antimicrobial agents: rifampin, vancomycin, ciprofloxacin, cotrimoxazole, cloxacillin, clindamycin, and daptomycin. Minimal Inhibitory Concentration (MIC) assays were determined according to EUCAST recommendations and breakpoints (5). Minimal Bactericidal Concentration (MBC) was also calculated by colony counting after plating the well contents.
RESULTS
Antibiotic susceptibility assay results are shown in tables 1 and 2. It is especially remarkable the high number of meticillin-resistant S. aureus (MRSA) strains. Cotrimoxazole and clindamycin showed better results for S. aureus. Rifampin, vancomycin, and daptomycin showed a very good activity, although some resistant strains were detected for the first two. MBC values showed a strain-dependant activity of rifampin and vancomycin. Only daptomycin showed bactericidal activity against all the tested strains.
DISCUSSION & CONCLUSIONS
The treatment of PJRI is still a challenge due to the variable antibiotic susceptibility and the growing number of multidrug-resistant strains. The high number of MRSA detected in our study, makes it necessary to search other antibiotics as an alternative to vancomycin, the traditional elective treatment. The high in vitro activity of daptomycin against the tested strains suggests that it could be an important alternative according to other promising results (6). Rifampin associated with other antimicrobials and cotrimoxazole, with a good in vitro activity against most MRSA strains, could be other potential strategies (7, 8).
