Effect of subinhibitory concentrations of antimicrobial agents on adherence to silicone and hydrophobicity of coagulase-negative staphylococci

Objectives To study the effect of 0.25 MIC of antimicrobial agents on adherence to silicone and hydrophobicity of a slime-producing Staphylococcus epidermidis (ATCC 35984) and non-slime-producing Staphylococcus hominis (ATCC 35982). Methods Adherence was assessed in vitro, using silicone rubber immersed in a suspension of bacteria, pretreated with 0.25 MIC of oxacillin, ceftriaxone, vancomycin or pefloxacin. After a 24-h period, adherent bacteria, detached by trypsin and sonication, were counted. Hydrophobicity was assessed by measuring the affinity of pretreated bacteria to p-xylene. Results For slime-producing S. epidermidis, adherence was significantly decreased by 81%, 91% and 77% with oxacillin, vancomycin and pefloxacin respectively. For non-slime-producing S. hominis, adherence was significantly decreased by 75% and 94% with oxacillin and ceftriaxone respectively. Hydrophobicity of both strains was significantly decreased with oxacillin only. Conclusions Adherence of coagulase-negative staphylococci onto silicone can be modified by sub-MICs of some of the antimicrobial agents tested. This effect was different in the slime-producing and non-slime-producing strains, and was not correlated with the mechanism of the inhibitory effect of these antimicrobial agents, or the modification of hydrophobicity. This suggests that some surface components, not involved in hydrophobicity, could play a role in in vitro adherence to silicone.