ObjectivesTo investigate the biofilm-forming related factors against MRSA bloodstream isolates and evaluates their clinical features and treatment outcomes by biofilm production.MethodsWe collected 126 consecutive methicillin-resistant Staphylococcus aureus (MRSA) causing blood stream infections (BSIs) at 10 tertiary hospitals from 2007 to 2009. We investigated biofilm-forming ability using a microtiter plate assay, and molecular characteristics including multilocus sequence typing, staphylococcal cassette chromosome mec and accessory gene regulator types. We compared the clinical characteristics and outcomes of patients infected with biofilm-forming and non-biofilm-forming MRSA isolates.ResultsOf the 126 samples, 86 (68.3%), including 5 strong level (OD570 ≥ 1.0) and 81 weak level (0.2 ≤ OD570 < 1.0), had biofilm-forming capacity. Detection of fibronectinbinding protein in biofilm-forming strains was significantly higher than biofilm non-forming ones (p = 0.001) and three enterotoxin genes (sec-seg-sei) islands had a high frequency regardless of biofilm production. However, biofilm-forming strains were more likely to be multidrug resistant (three or more non-β-lactam antibiotics) than biofilm non-forming ones [79.2% vs. 59.2%, p = 0.015, odds ratio (OR) 2.629, 95% confidence interval (CI) 1.92–5.81]. Clinical features of patients with BSIs caused by biofilm-forming MRSA strains were more likely to be hospital onset [77.9% vs. 60.0%, p = 0.024, OR 2.434, 95% CI 1.11–5.33) and more frequently occurred in patients with use of invasive devices [85.7% vs. 61.2%, p = 0.002, OR 3.879, 95% CI 1.61–8.97]. The other clinical features were compared with the clinical outcomes of the two groups and were not significant (p > 0.05).ConclusionBiofilm-forming MRSA strains showed higher frequency of fnbB gene than biofilm non-forming ones and more incidence rates on particular genotypes. And, their patient's features were not significantly different between two groups in this study, except for several clinical factors.

We identified 25 high-level mupirocin-resistant (MuH) and 21 low-level mupirocin-resistant (MuL) Staphylococcus aureus isolates from eight long-term-care facilities (LTCFs). The pulsed-field gel electrophoresis patterns of 19 MuH and 19 MuL isolates from two facilities were identical for 18 and 15 isolates, respectively. The most predominant mupA restriction fragment length polymorphism type was found in 21 MuH isolates. We conclude that clonal transmission of MuH and MuL S. aureus strains occurred in these LTCFs. This is the first report of clonal transfer of mupirocin resistance in LTCFs.Colonization and infection with Staphylococcus aureus are common in older people in long-term-care facilities (LTCFs) (1, 2, 4). The prevalence of S. aureus colonization and infection, which result primarily from methicillin-resistant strains, has recently been reported by chronic care facilities worldwide (1,3,6,7). Mupirocin calcium ointment is a topical antibiotic indicated for the eradication of nasal carriage of staphylococci, including methicillin-resistant strains. Mupirocin alone or in combination with other antimicrobial agents decreases S. aureus colonization among residents of LTCFs (3,7,8,20). Several outbreaks of methicillin-resistant S. aureus colonization and infection in LTCFs have been reported, and until now, it was thought that the application of mupirocin ointment might help break the chain of transmission. However, the extensive use of this agent has led to the rapid emergence of mupirocinresistant strains in different parts of the world (9,16,11,13,18,19). To our knowledge, there are no reports on the prevalence and outbreak of mupirocin-resistant S. aureus in LTCFs. In South Korea, mupirocin ointment has been used since 1994 to eradicate staphylococcal infection in hospitals, and the prevalence and mechanisms of mupirocin-resistant staphylococci were first reported in 2003 (23).We investigated the clonal transmission of high-level mupirocin-resistant (MuH) and low-level mupirocin-resistant (MuL) S. aureus and the mupA gene polymorphisms of MuH S. aureus strains in LTCFs. Seven hundred forty-nine swab specimens were obtained from patients of eight LTCFs from July to August 2002. Nasal swab specimens were obtained from 632 patients (one isolate per patient), and 117 infection swab samples were obtained from infected sites (e.g., sore, wound, or trachea) present in these patients. Swab specimens were cultured on staphylococcal broth (Trypticase soy broth [TSB]) medium for 24 h at 35°C. Mannitol salt agar and mannitol salt oxacillin agar supplemented with 6 g/ml oxacillin were used to isolate S. aureus and methicillin-resistant S. aureus, respectively. Initial identification was based on colony morphology, Gram staining, the coagulase test using the Staphaureux latex agglutination kit (Murex Biotech Ltd., Dartford, United Kingdom), and thermonuclease production with DNase medium (Becton Dickinson, Franklin Lakes, NJ). When necessary, further confirmatory tests were performed using a Vitek system (bioMerieux,...

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) are important pathogens causing nosocomial infections in Korean hospitals. This study aimed to investigate the epidemiological and genetic diversity of clinical S. aureus isolates in healthcare settings from 2001 to 2008.MethodsSamples and data were obtained from 986 individuals as part of the National Antimicrobial Surveillance Project, involving 10 regions nationwide. Molecular typing studies, including multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) typing were performed, and a representative clone of Korean MRSA was classified by combinational grouping using a DiversiLab (DL; bioMérieux, France) repetitive element polymerase chain reaction (rep-PCR) system.ResultsNine Korean MRSA clones (KMRSA-1 to -9) were identified by analysis of genetic backgrounds and molecular characteristics. KMRSA-1 to -3, expressing clonal complex (CC) 5 (carrying SCCmec II), CC8 (carrying SCCmec III), and CC72 (carrying SCCmec IV) were spread nationwide. In contrast, KMRSA-6 was highly prevalent in Gyeongsangnam-do, and KMRSA-4 was highly prevalent in Jeollanam-do and Jeollabuk-do.ConclusionsEpidemic KMRSA clones were genetically similar to major clones identified from the USA, with the exception of KMRSA-2, which had the SCCmec III type. Our results provide important insights into the distribution and molecular genetics of MRSA strains in Korea and may aid in the monitoring of MRSA spread throughout the country.

In addition to vancomycin-intermediate Staphylococcus aureus (VISA), S. aureus with a vancomycin MIC of 4 microg/ml has been reported to be the cause of therapeutic failure. This study was designed to determine the prevalence of methicillin-resistant S. aureus (MRSA) with a vancomycin MIC of 4 microg/ml and to clarify the clinical characteristics of infections caused by these isolates. During the 8-week period from April to May, 2001, 27 hospitals participated in a nationwide surveillance program for VISA and vancomycin-resistant S. aureus (VRSA) in Korea. After screening on brain-heart infusion agar containing 4 microg/ml of vancomycin as previously described, 100 isolates with confluent growth were tested. The medical records of the patients involved were reviewed. Even though VISA or VRSA was not detected among 3,756 MRSA isolates, 18 (0.5%) had a vancomycin MIC of 4 microg/ml. The infections in 12 of these patients, excluding 5 that were colonized, were 8 chronic osteomyelitis, 1 surgical site infection, 1 pneumonia, 1 intra-abdominal infection, and 1 catheter-related infection. Although 11 cases were exposed to glycopeptides for a long time (median 56 days), the site of infection became culture-negative in only 1 case. Two patients died of their S. aureus infections. MRSA with a vancomycin MIC of 4 microg/ml was rare. Chronic osteomyelitis was the most common type of infection, and prolonged exposure to glycopeptides was associated with reduced susceptibility to vancomycin.

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