Characteristic cell wall ultrastructure of a macrolide-resistant Staphylococcus capitis strain isolated from a patient with chronic sinusitis.

Fourteen-membered-ring macrolides have an antiinflammatory effect, in addition to their antibacterial effect, and are widely used at low dosages for long-term therapy for chronic inflammatory disease such as diffuse pan-bronchiolitis and chronic sinusitis. A macrolide-resistant coagulase-negative staphylococcal strain was obtained from the maxillary sinus of a patient with chronic sinusitis, who failed long-term macrolide therapy. The isolated strain was characterized as Staphylococcus capitis and had an MIC for erythromycin greater than 128 microg/ml. Morphological observation demonstrated that this macrolide-resistant S. capitis strain had a thicker cell wall than macrolide-sensitive S. capitis strains. Moreover, the strain was not carrying any other than the four genes that are known mainly to encode for macrolide resistance in S. aureus. Therefore, the strain had an unknown macrolide-resistance mechanism that might be related to cell wall thickening.