Clinical relevance of antibiotic resistance among propionibatteria carried by acne patients in Ferrara (Italy) is discussedAim. Antibiotics reducing the number of propionibacteria on the skin represent powerful agents in the treatment of inflammatory acne. The widespread use of both oral and topical antibiotics to treat acne has resulted in the dissemination of propionibacterial-resistant strains. Failure of therapy associated with the selection of antibiotic-resistant propionibacteria is a well recognized concern. The aim of the study is to determine the prevalence of skin colonization by antibiotic-resistant propionibacteria in a large number of acne patients attending our department and to monitor changes over a six-year period (April 2000-October 2005). Methods. From April 2000 we have tested the susceptibility to the most commonly used antiacne antibiotics of the propionibacterial strains carried by the patients with acne, proposed to be treated with antibiotic. Propionibacterial samples were obtained from the skin surface of the face of 1579 acne patients using a moistened swab. The swabs were used to inoculate agar plates containing selective concentrations of tetracycline, minocycline, erythromycin and clindamycin, as well as antibiotic-free control plates. After 7 days of anaerobic incubation at 37 °C, a semiquantitative method (a scale from 0 to 5+) was applied to estimate the amount of growth in the presence of each antibiotic. Results. Propionibacteria were isolated in 1508 of 1579 patients sampled. The prevalence of carriage of isolates resistant to at least one antibiotic was 55.9%. Resistance to erythromycin was the most common in all years ranging from 58.8% in 2000 to 38.5% in 2005 (mean prevalence 47.7%); resistance to clindamycin ranged from 44.1% in 2000 to 32.2% in 2005 (mean 39.2%). Thirty-five percent of the isolated strains were resistant to both erythromycin and clindamycin. Rates of resistance to tetracyclines were very low (1.9% to tetracycline and 0.6% to minocycline). Mild reduction in resistance to erythromycin and clindamycin was noticed over the period of samples collection. The highest rates of resistance were found in older patients and slightly higher rates in males than in females. Conclusion. The available data show a wide distribution of propionibacterial strains resistant to erythromycin and clindamycin in the large number of patients sampled. At present, resistance rates to oral tetracyclines are very low. These findings support the significance of the cultural definition of antibiotic sensitivity of propionibacteria isolated from acne patients. This is considered by us useful for both adequate management of acne and monitoring the phenomenon of bacterial resistanc
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