Resistance of Staphylococcus aureus to fusidic acid

We read with great interest the report by Nishijim et al . entitled, “Antimicrobial resistance of Staphylococcus aureus ( S. aureus ) isolated from impetigo patients between 1994 and 2000. ” The authors describe the antimicrobial susceptibility in vitro of S. aureus isolated from impetigo patients from the Department of Dermatology, Kansai Medical University Center, Japan, between 1994 and 2000. In Japan, topical gentamicin is often prescribed for impetigo. The minimum inhibitory concentration (MIC) of gentamicin is high, but has not increased in this period. Despite the increasing use of fusidic acid in an ointment with gentamicin, no S. aureus isolates were found to be resistant to fusidic acid between 1994 and 2000. This ointment is apparently very effective for impetigo and the authors strongly recommend its prescription. Our observations do not confirm their data. We reviewed the resistance pattern of S. aureus to fusidic acid in patients with atopic dermatitis at our dermatology in-patient department. 1 Our department is a tertiary referral center for patients with atopic dermatitis. We routinely monitor patients for their S. aureus carrier state on the first day of hospitalization. Between 1995 and 2001, the rate of resistance to fusidic acid increased from 9.7% to 23.4% (Table 1). The rate of resistance to methicillin remained stable at around 0.5% during this period. The majority of patients with atopic dermatitis have used topical fusidic acid prior to hospitalization for prolonged periods of time to treat infected eczema or to control their S. aureus carrier state. Between 1989 and 1995, drug resistance amongst S. aureus isolates was monitored in The Netherlands. 2 The resistance of S. aureus isolates to fusidic acid was only 0.2% of the 6526 samples tested. Arkwright et al . 3 studied the antimicrobial resistance of Staphylococcus and Streptococcus taken from patients attending the Regional Paediatric Atopic Dermatitis Clinic, Manchester, UK, in whom there was a clinical suspicion of secondary impetigo; 51% of children older than 5 years had fusidic acid-resistant S. aureus , compared with 38% of children aged 1–5 years and 14% of infants younger than 12 months. In contrast, in about 140 children with impetigo seen in primary care centers in The Netherlands, none of the S. aureus isolates showed resistance to fusidic acid. 4 These authors also recommend topical fusidic acid as first-choice treatment in patients with impetigo at the primary care level. Ravenscroft et al . 5 investigated the possible reasons for the increase in fusidic acid-resistant S. aureus from below 4% to 8–10% in Harrogate, UK. Resistant strains were frequently found in patients with chronic cutaneous infections (68%), and 44% had been given topical fusidic acid within the preceding 6 months. It seems plausible that prolonged topical use of fusidic acid is the main cause of the increase in fusidic acid-resistant S. aureus , especially in patients with chronic dermatitis, such as atopic dermatitis. We believe that the topical preparation of fusidic acid is being prescribed too generously and for too long a time in this patient group in our setting. Therefore, we advise that fusidic acid should be used for infected dermatitis only and for short periods of time of about 2 weeks. We hope that the prudent use of this topical antimicrobial will reverse the trend of increasing resistance observed in our patients. It may be hypothesized that the low rate of resistance to fusidic acid in the Japanese study is related to the addition of gentamicin to fusidic acid in the same ointment. More research is needed to confirm this.