Prevalence and genetic diversity of Staphylococcus aureus small-colony variants in cystic fibrosis patients

Abstract

Staphylococcus aureus small-colony variants (SCVs) are being isolated more frequently in cystic fibrosis (CF) patients. We aimed to determine the prevalence of S. aureus SCVs and their phenotypic and genotypic properties in CF patients admitted to a university hospital. Specimens of 248 patients were examined during a period of 11 months. Colonies supposed to be SCVs were evaluated on Columbia blood agar, mannitol salt agar, and brain–heart infusion agar with 5% NaCl (BHIA 5% NaCl). Strains were confirmed by S. aureus nucA PCR. Antibiotic susceptibilities of SCVs and simultaneously isolated S. aureus strains were determined for oxacillin, gentamicin, trimethoprim–sulphamethoxazole, vancomycin, ciprofloxacin, linezolid, and tigecycline. Genetic relatedness between SCVs and normal S. aureus strains was determined with a pulsed-field gel electrophoresis (PFGE) method. S. aureus SCVs were detected in 20 of 248 patients (8.1%). The highest SCV isolation rate was obtained with MSA, followed by BHIA 5% NaCl. Auxotrophism for thymidine was demonstrated in six SCVs. The tigecycline susceptibilities of 48 SCV strains isolated in this study showed higher MIC values than those of 33 simultaneously isolated normal S. aureus strains. Whereas SCVs and normal S. aureus strains showed identical genotypes in 14 of the patients, five patients showed different genotypes. This first study from Turkey evaluating S. aureus SCVs in CF patients has indicated the importance of considering and reporting SCVs in chronic infections such as CF. The presence of SCVs will probably indicate persistent infection, and this might impact on antibiotic treatment decisions, as they are more resistant to antibiotics.