Biomaterial-associated infection of gentamicin-loaded PMMA beads in orthopaedic revision surgery

In two-stage orthopaedic revision surgery, high local levels of antibiotics are achieved after removal of an infected prosthesis through temporary imp lantation of gentamicin-loaded beads. However, despite their antibiotic rel ease, these beads act as a biomaterial surface to which bacteria preferenti ally adhere, grow and potentially develop antibiotic resistance. Gentamicin -loaded beads were retrieved from 20 patients with prosthesis-related infec tions. Excised tissue samples were taken for routine culture, while beads w ere analysed in an extensive laboratory procedure. Extensive culture proced ures indicated the presence of bacteria on gentamicin-loaded beads in 18 of the 20 patients involved, while 12 of these 18 patients were considered fr ee of infection by routine culture. Nineteen of 28 bacterial strains isolat ed were gentamicin resistant and cultures from three patients yielded highl y gentamicin-resistant sub-populations. It is concluded that routine cultur e of excised tissues in orthopaedic revision surgery is inadequate to ascer tain full eradication of infection, especially as infecting, antibiotic-res istant bacteria preferentially adhere to and grow on gentamicin-loaded bead s. Extensive examination of the bead surfaces is proposed as a more reliabl e indication that infection has been eradicated.