1586. In Vitro Activity of Rifampin, Rifabutin, Rifapentine, and Rifaximin Against Biofilms Formed by Staphylococci Isolated from Prosthetic Joint Infection

BACKGROUND: Prosthetic joint infections (PJIs) are serious complications after total joint arthroplasty. Staphylococcus aureus and Staphylococcus epidermidis, which are proficient biofilm-formers, account for ~60% of PJI cases. Therapy often includes rifampin because of its anti-biofilm activity; the activity of other rifamycins against staphylococcal biofilms is poorly defined. This study evaluated the in vitro activity of rifampin, rifabutin, rifapentine, and rifaximin against S. aureus and S. epidermidis biofilms formed by isolates from patients with PJI. METHODS: 200 staphylococcal isolates were tested (111 S. aureus and 89 S. epidermidis). All S. aureus isolates, and all except 7 S. epidermidis isolates, were rifampin susceptible. Rifampin, rifabutin, rifapentine, and rifaximin minimum biofilm inhibitory concentrations (MBICs) and minimum biofilm bactericidal concentration (MBBCs) were determined using a pegged lid microtiter plate assay. RESULTS: Rifampin-resistant isolates had MBICs and MBBCs ≥16 µg/mL. Results for the rifampin-susceptible isolates are shown. All 193 rifampin-susceptible isolates had rifampin MBICs ≤1 µg/mL (rifampin-susceptible breakpoint for planktonic susceptibility testing), with 1, 2, and 2 isolates having MBICs > 1 µg/mL for rifabutin, rifapentine and rifaximin, respectively. S. aureus MBBC(50) values were 8, 1, 2 and 4 µg/mL for rifampin, rifabutin, rifapentine and rifaximin, respectively. S. epidermidis MBBC(50) values were 2, 0.06, 0.25, and 0.5 µg/mL for rifampin, rifabutin, rifapentine and rifaximin, respectively, for rifampin-susceptible isolates. CONCLUSION: Rifabutin and rifapentine, and to a lesser extent, rifaximin, show promising in vitro activity against rifampin-susceptible staphylococcal biofilms formed by isolates associated with PJI; studies evaluating in vivo activity are warranted. [Image: see text] DISCLOSURES: All authors: No reported disclosures.