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Small-Colony Variants in Persistent and Recurrent Staphylococcus aureus Bacteremia
Nak-Hyun Kim1, Yu Min Kang1, Woong Dae Han2
11 Department of Internal Medicine, Seoul National University College of Medicine , Seoul, Republic of Korea.
Microbial Drug Resistance (Larchmont, N.Y.)
|March 17, 2016
Summary
Small-colony variants (SCVs) of Staphylococcus aureus can cause persistent infections and treatment failure. Identifying these slow-growing SCVs is challenging but crucial for effective patient management.
Area of Science:
- Microbiology
- Infectious Diseases
- Medical Diagnostics
Background:
- The small-colony variant (SCV) phenotype in Staphylococcus aureus is linked to persistent intracellular infections, decreased antibiotic susceptibility, and treatment challenges.
- Identifying SCV infections is difficult due to their slow growth and atypical morphology.
Observation:
- SCVs were identified in two patients with persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia following cardiothoracic surgery.
- Nine blood isolates exhibited pinpoint, nonpigmented, nonhemolytic colonies, reverting to normal morphology on Schaedler agar and showing hemin dependence.
Findings:
- All isolates were confirmed as MRSA and belonged to a single clone (ST5, SCCmec type II, agr type II, spa type t2460).
- Vancomycin susceptibility was maintained (MIC 1.0 μg/mL).
- No relA mutations or hypervirulent SCV (hVISA) phenotype were detected.
Implications:
- Persistent S. aureus bacteremia warrants a high index of suspicion for the SCV phenotype.
- Consideration of SCVs is vital for diagnosing and managing difficult-to-treat S. aureus infections.
- This study highlights the importance of recognizing SCV characteristics in clinical settings.
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