Characteristics of Adherence to Plastic Tissue Culture Plates of Coagulase-negative Staphylococci Exposed to Subinhibitory Concentrations of Antimicrobial Agents

Adherence and hydrophobic properties characteristic of 6-h cultures of coagulase-negative staphylococci on plastic tissue culture plates were determined after the organisms had been treated for up to an additional 6 h with subinhibitory concentrations of antimicrobial agents. Clindamycin, erythromycin, norfloxacin, tunicamycin, and vancomycin had no effect. Cephalothin, chloramphenicol, gentamicin, imipenem, methicillin, novobiocin, polymyxin B, rifampin, and tobramycin had varied effects. Most changes induced by these agents resulted in differing degrees of inhibition of adherence. However, an increase in adherence of 65% was observed for one strain, RP14 (ATCC 35981), with rifampin treatment. Hydrophobicity of coagulase-negative staphylococci treated with antimicrobial agents measured by using a biphasic system with hexadecane showed excellent correlation with adherence (r = .958, P less than .0005), a result suggesting that adherence of these bacteria in this system depends heavily on hydrophobic surface moieties. Transmission electron microscopy of drug-treated coagulase-negative staphylococci revealed only an increase in cell-wall thickness, regardless of whether adherence was increased or decreased.