Accessory Gene Regulator Polymorphism and Vancomycin Minimum Inhibitory Concentration in Methicillin-Resistant Staphylococcus aureus

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia with a vancomycin minimum inhibitory concentration (MIC) of 2 microg/mL presents a high rate of therapeutic failure in response to vancomycin. In addition, polymorphism in accessory gene regulator (agr) is associated with vancomycin therapeutic effects. The association between agr polymorphism and vancomycin MICs was investigated in MRSA isolates. METHODS: Agr group-specific PCR was conducted on 118 MRSA bloodstream isolates. Vancomycin susceptibility tests were conducted, while E-test GRD (bioMerieux SA, France) was used to detect heterogeneous vancomycin-intermediate S. aureus (hVISA). RESULTS: Of the 118 MRSA isolates, 59 (50.0%), 43 (36.4%), and 10 (8.5%) isolates belonged to agr group I, II, and III, respectively. Six isolates could not be classified. Twenty-six, 73, and 19 isolates presented a vancomycin MIC of 2, 1, and 0.5 microg/mL, respectively. Nine (34.6%), 14 (53.8%), and 2 (7.7%) isolates with MICs of 2 microg/mL belonged to agr group I, II, and III, respectively. Thirty-seven (50.6%), 26 (35.6%), and 6 (8.2%) isolates with MICs of 1 microg/mL belonged to agr group I, II, and III, respectively. Thirteen (68.4%), 3 (15.8%), and 2 (10.5%) isolates with MICs of 0.5 microg/mL belonged to agr group I, II, and III, respectively. The agr group II presented more isolates with MIC of 2 microg/mL (32.6%) than the agr non-group II (16%). Four isolates tested positive for hVISA. Three of them belonged to agr group II. CONCLUSIONS: MRSA isolates with vancomycin MIC of 2 microg/mL were more common in agr group II than in agr non-group II.

Accessory Gene Regulator Group Polymorphisms in Methicillin-Resistant Staphylococcus aureus: An Association with Clinical Significance

PURPOSE: Virulent gene expression in Staphylococcus aureus is controlled by regulators such as the accessory gene regulator (agr). Strains can be divided into four major agr groups (agr I-IV) on the basis of agrD and agrC polymorphisms. The purpose of this study was to define the proportion of agr I, II, and III polymorphisms and to compare the clinical characteristics between group I and non-group I polymorphisms of methicillin-resistant Staphylococcus aureus (MRSA) strains in a Korean tertiary care teaching hospital. MATERIALS AND METHODS: A total of 158 clinical isolates were evaluated by RFLPs (restriction fragment length polymorphisms). RESULTS: The mean age of the patients was 50.2 +/- 21.9 years old. There were 74 (49.3%), 66 (44.0%), 10 (6.7%), 7 (4.4%), and 1 (0.6%) strains in agr group I, II, III, I + II, and I + III polymorphisms, respectively. Only ear infections were a statistically significant clinical parameter according to univariate (p=0.001) and multivariate analysis (OR, 4.721 (1.273-17.508), p=0.020). CONCLUSION: This study suggests that agr group I is the most prevalent in Korea, and ear infections are correlated with the group I polymorphism, which is a different clinical trend from western countries. It can also be inferred that community-acquired MRSA correlates with agr group I.