Staphylococcus epidermidis biofilms: unexpected outcome of double and triple antibiotic combinations with rifampin.

Staphylococcus epidermidis, in contact with artificial surfaces, may produce a protective glue-like matrix or biofilm. The authors demonstrated that rifampin alone among 35 antibiotics penetrated the biofilm within a 24 hr exposure producing a major but incomplete killing. Antibiotics of the cell-wall active class (including vancomycin) were synergistic with rifampin, completing the bactericidal action. The addition of these antibiotics to a rifampin-vancomycin combination did not alter the synergy. Other antibiotics (including aminoglycosides) antagonized rifampin activity. This antagonism of rifampin was maintained when the antibiotics were added to the rifampin-vancomycin synergistic combination. These results may have implications for the choice of optimal therapeutic regimens in the management of implant-associated infection.