Influence of bacterial adherence to intravascular catheters on in-vitro antibiotic susceptibility

Slime-producing and non-slime-producing strains of coagulase-negative staphylococci (CNS) were evaluated for nafcillin susceptibility in the presence and absence of polyvinylchloride (PVC) catheters. Semiquantitative roll cultures of catheters with adherent organisms after exposure to predicted bactericidal concentrations of nafcillin were carried out to assess survival of these organisms. Slime-producing and non-slime-producing CNS had similar minimum inhibitory (MIC) and bactericidal (MBC) concentrations in the absence of catheters and similar MIC in the presence of catheters. However, the mean MBC of slime-producing CNS, and to a lesser extent of non-slime-producing strains was higher in the presence than in the absence of catheters. Slime-producing CNS were recovered from PVC catheters after overnight incubation in cidal concentrations (greater than 4.0 micrograms/ml) of nafcillin (average 350 colony-forming units per 1 cm). Thus nafcillin-sensitive CNS strains, particularly those producing slime, are able to survive exposure to cidal concentrations of the drug when adherent to PVC catheters.