Abstract:

Objective To identify a clinical isolate of Staphylococcus aureus small colony variant and investigate its antibiotic resistance and auxotroph type, so as to provide a basis for the prevention and control of small colony variant infection. Methods One possible Staphylococcus aureus small colony variant strain was isolated from pus of brain tumor resection site of a patient. The bacterial colony morphology, biochemical characteristics and susceptibility test of this small colony variant strain were identified. Staphylococcus aureus specific gene nuc and methicillin resistance-associated gene mecA were detected and sequenced. Complementation test was used to identify the type of auxotroph. Results The strain was identified as Staphylococcus aureus by Vitek-2 Compact system, which contained Staphylococcus aureus specific gene nuc and methicillin resistance-associated gene mecA. Its major phenotypes included small colony, slow growth, indistinct zone of hemolysis (24 h), decreased coagulase and positive catalase reaction. This clinical isolate of Gram positive cocci in grape like clusters was resistant to β-lactam antibiotics, and complementation test showed that the growth of this clone was CO₂dependent. Conclusion One CO₂-dependent methicillin resistant Staphylococcus aureus small colony variant strain was isolated and identified, which laid the groundwork for the control and prevention of Staphylococcus aureus small colony variant strain-associated disease and research of its pathogenic mechanism.

Key words: Staphylococcus aureus, small colony variants, isolation and identification, CO₂-dependent