The effect of peritoneal dialysis solutions on rifampin action against Staphylococcus epidermidis in the fluid and biofilm phases of growth

Abstract

Continuous ambulatory peritoneal dialysis (CAPD) catheter-associated infections can be resistant to conservative therapeutic measures despite the apparent susceptibility of the infecting bacterial strains to antibiotics. This chronicity of infection has been ascribed to the development of bacteria on the surfaces of catheter material within a protective polysaccharide shield or matrix. CAPD catheters are unique in being exposed to nonphysiological environments of dialysis fluids of varying physical properties and constitution. We determined that the rate of growth of S. epidermidis in the fluid phase In laboratory media or fresh dialysis solution was significantly influenced by pH. An acid milieu (pH 5) impaired growth compared to a neutral milieu (pH 7). Spent dialysis fluid, however, which had an approximately neutral pH, also impaired bacterial growth, the assumption being that this results from properties of spent fluid unrelated to pH. Using rifampin as the test antibiotic, we noted that its action on S. epidermidis was unaffected by pH or by the differing milieu of fresh and spent fluid. Bacterial growth was arrested regardless of the milieu. We further examined the potential of dialysis fluids to modify the interaction between rifampin and the matrix-enclosed bacteria of standardized S. epidermidis biofilms. We determined that the pH of the dialysis solution was a critical factor influencing the outcome of exposure of the biofilm to rifampin. An acid pH enhanced antibiotic activity, whereas a neutral pH was associated with antibiotic antagonism. These findings have implications in the management of S. epidermidis catheter-associated infections using rifampin. Administration of the antibiotic in fresh peritoneal dialysis solution (pH 5.6) is judged more likely to be associated with a successful outcome.