Synergistic Effect of a Novel Focal Hyperthermia on the Efficacy of Rifampin in Staphylococcal Experimental Foreign-body Infection

This study was designed to evaluate the efficacy of focal hyperthermia and rifampin in vitro and in vivo using a rabbit model of foreign-body infection by methicillin-resistant Staphylococcus aureus (MRSA). In vitro studies demonstrated bacterial re-growth and development of rifampin resistance after 24 h with rifampin alone, which was prevented under hyperthermic conditions. For the in vivo studies, rifampin was administered intraperitoneally every 12 h for 7 days to rabbits with MRSA-containing cages implanted into their flanks. When combined with hyperthermia at 39 degrees C, 41 degrees C and 43 degrees C, rifampin significantly reduced in-cage bacterial counts by > 3.0 log(10) colony forming units/ml compared with rifampin alone. Eradication of cage-associated infection was achieved more effectively when rifampin was combined with hyperthermia, with cure rates of 70 - 95% on day 10. Focal hyperthermia combined with rifampin prevented the emergence of rifampin resistance and maintained rifampin efficacy. These findings might have implications for orthopaedic surgery.