A Case of Methicillin-Resistant Staphylococcus aureus Small Colony Variants(SCVs) Isolated from Urine of a Patient with Persistent and Relapsing Bladder Stone / 대한임상미생물학회지

ABSTRACT

Methicillin-resistant Staphylococcus aureus colony variants (SCVs) are frequently auxotrophic for hemin, menadione, thiamine, and CO2 involved in biosynthesis of the electron transport chain element. This phenotype grows slowly, and forms very small, nonhemolytic colonies in routine culture, so it may be led to the misidentification of this organism. We isolated an organism with catalase-positive, gram-positive cocci in cluster from the urine of a 55-years-old woman with persistent and relapsing bladder stone, who had undergone the antibiotic treatment with cefotaxime, ceftizoxime, amikacin, and/or micronomicin, intermittently for three years. The possibility of SCVs should have been ruled out because this organism didn't grow on Mueller-Hinton agar (MHA) for the susceptibility test. It formed small colonies on blood agar plate overnight, and grew only on MHA with supplement of hemin, or with 5% CO2. This organism was coagulase-positive, DNase-positive, manitol-salt positive, and identified as S. aureus with VITEK GPI card. The susceptibility test could be performed after adding hemin(1mg/mL) into bacterial suspension and showed susceptibility against vancomycin, teicoplanin, and rifampin. Because these phenotypes can be misidentifide as other non-pathogenic organisms due to their atypical characteristics, we should consider SCVs in case of small, nonhemolytic colonies with catalase-positive, gram-positive cocci in cluster, showing no growth on MHA. In addition, infections caused by SCVs are recently recognized in relation to persistent and relapsing infection, so they could be isolated from the patients with long-term antibiotic therapy.