Abstract
BackgroundStrains of Staphylococcus aureus with an intermediate level of resistance to vancomycin (vancomycin-intermediate S. aureus, or VISA) or which contain subpopulations of mixed susceptibility (heterogeneous VISA, or hVISA) have been reported worldwide. However, the prevalence of VISA and hVISA infections in Northeast China is unknown. From 2007 through 2010, we surveyed the vancomycin susceptibility of methicillin-resistant and methicillin-sensitive S. aureus (MRSA and MSSA, respectively) clinical isolates in Northeast China.Methods S. aureus clinical isolates (369 MRSA and 388 MSSA) were screened for hVISA and VISA on brain heart infusion agar containing 3 μg/mL vancomycin, and their identity confirmed using a modified population analysis profile-area under the curve method and broth microdilution. All hVISA and VISA isolates were characterized genotypically and phenotypically.ResultsTen percent and 0.5 percent of the isolates were hVISA and VISA, respectively. The proportion of hVISA among MSSA isolates for the entire study period was 4.1%, but increased significantly year-by-year, from 1.2% in 2007 to 7.2% in 2010. The predominant sources of hVISA and VISA isolates were sputum (56.3%), pus (18.8%), and blood (8.8%). Molecular typing of hVISA and VISA strains revealed that, taken together, 80% contained the accessory gene regulator (agr) group II, and of these, 85.7% of the MR-hVISA and MR-VISA strains were staphylococcal cassette chromosome mec (SCCmec) type II. The adherence ability of all hVISA and VISA strains was reduced compared with that of vancomycin-susceptible strains, shown by biofilm assay.ConclusionsThe percentage of hVISA strains was high and increased each year. The proportion of hVISA among MSSA specifically also increased significantly each year. In isolates collected from diverse infection sites, hVISA and VISA strains were found predominantly in sputum, pus, and blood, in descending order. Testing for vancomycin susceptibility should include both MRSA and MSSA isolates collected from different clinical sites.
Highlights
Staphylococcus aureus is a ubiquitous bacterium responsible for both community-associated and hospital-acquired infections, which range in severity from non-pathogenic to life threatening [1]
The number of isolates tested in each year were: 2007, n = 171 (88 methicillin-resistant S. aureus (MRSA) and 83 MSSA); 2008, n = 183 (89 MRSA and 94 MSSA); 2009, n = 197 (97 MRSA and 100 MSSA) and 2010, n = 206 (95 MRSA and 111 MSSA)
Seventy-six (60 MRSA and 16 MSSA) of the 209 isolates were confirmed as hVISA via the population analysis profile-area under the curve (PAP-AUC) approach, and four
Summary
Staphylococcus aureus is a ubiquitous bacterium responsible for both community-associated and hospital-acquired infections, which range in severity from non-pathogenic to life threatening [1]. These infections, especially those due to methicillin-resistant S. aureus (MRSA), have been treated for more than a half-century primarily with the glycopeptide antibiotic vancomycin. Strains of Staphylococcus aureus with an intermediate level of resistance to vancomycin (vancomycinintermediate S. aureus, or VISA) or which contain subpopulations of mixed susceptibility (heterogeneous VISA, or hVISA) have been reported worldwide. From 2007 through 2010, we surveyed the vancomycin susceptibility of methicillin-resistant and methicillin-sensitive S. aureus (MRSA and MSSA, respectively) clinical isolates in Northeast China
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