High prevalence of inducible clindamycin resistance among Staphylococcus aureus isolates from patients with cystic fibrosis

BackgroundStaphylococcus aureus (SA) is an important pathogen among patients with cystic fibrosis (CF). Inducible clindamycin resistance (ICR) has been described as a cause of treatment failure in non-CF related infections. The prevalence of ICR among SA from patients with CF is unknown.MethodsWe compared clindamycin susceptibilities of SA isolated from patients with and without cystic fibrosis (CF) using hospital microbiology data. Patients with CF were primarily identified using CF registry data. We evaluated all patients who had SA isolated at the Children's Healthcare of Atlanta microbiology laboratory during May 2004–May 2005. We performed antimicrobial susceptibility testing using broth microdilution and performed D-zone testing for ICR in accordance with the Clinical Laboratory Standards Institute (CLSI) document M100-S16. Proportions were compared using a 2-sided Pearson's Chi-square test or Fisher's exact test to assess for significance.ResultsOf 703 patients with methicillin-resistant SA (MRSA), 48% of CF patients (68/143) had at least one isolate demonstrating ICR, compared to 8% of non-CF patients (43/560) (P < 0.01). Of 762 patients with methicillin-susceptible SA (MSSA), 29% of CF patients (73/254) had at least one isolate demonstrating ICR compared to 17% of non-CF patients (88/508) (P < 0.01).ConclusionsSA demonstrating ICR are significantly more prevalent among patients with CF than among those without CF.