Effect of antibiotics on cell surface hydrophobicity of bacteria causing orthopedic wound infections

Despite antibiotic prophylaxis and treatment, the incidence of wound infections in orthopedic surgery is significant. Postoperative wound infection is a multifactorial process, which can be modified by several bacterial factors. Cell surface hydrophobicity of bacteria is a very important physicochemical feature, which has a great influence on the ability of bacteria to adhere to the surface of host cells or medical implants.

In this study, the hydrophobic properties of thirteen bacterial strains (coagulase-negative staphylococci, Staphylococcus aureus and Pseudomonas aeruginosa) isolated from patients with postoperative deep wound infections following orthopedic procedures were determined by the salt aggregation test. Results were compared to the hydrophobicity of three Hungarian standard bacterial strains. The modifying effect of four antibiotics (cefuroxime, cefotaxime, amoxicillin combined with clavulanic acid and amikacin)--applied most often in our Department for prophylaxis and treatment of patients--were analyzed.

The cell surface hydrophobicity of certain strains showed considerable changes after antibiotic treatment. These alterations indicated the decrease in hydrophobicity. Supra-inhibitory concentrations (2x minimum inhibitory concentrations, MIC) of the antibiotics were able to induce more frequent alterations in hydrophobicity than sub-inhibitory (0.5x MIC) levels.

Alterations in cell surface hydrophobicity caused by antibiotics can modify the adhesion process and thus the pathogenicity of bacterial strains. These changes should be taken into consideration in the management of proper antibiotic prophylaxis and in the treatment of orthopedic patients.