| Summary: | 博士 === 國防醫學院 === 醫學科學研究所 === 100 === Background: Staphylococcus aureus causes a variety of severe infections such as bacteremia, skin and soft tissue infection, pneumonia, osteoarticular infections, and sepsis. Methicillin-resistant S. aureus (MRSA) emerged since 1960s and accounted for 60-80% of S. aureus in Taiwan. Differences existed in molecular and phenotypic characters have been identified between community-associated MRSA (CA-MRSA) and hospital-associated MRSA (HA-MRSA). Limited MRSA clones were found to circulate worldwide and in certain geographic areas. The goals of this study were to delineate the molecular and phenotypic characteristics and the correlations between them in MRSA bloodstream isolates. Materials and Methods: CA-MRSA and HA-MRSA isolates from patients with septic arthritis and MRSA isolates from bacteremic patients were collected from 2003 database of Surveillance of Multicenter Antimicrobial Resistance in Taiwan (SMART) program. These isolates were assigned with PCR and nucleotide sequencing based on polymorphisms in agr, SCCmec, MLST, spa, and dru. Phenotypes were characterized with gene encoding Panton-Valentine leucocidin (pvl), inducible macrolide-lincosamide-streptogramin B resistance (MLSBi), antibiogram by disc diffusion, minimal inhibitory concentration (MIC) to vancomycin (VA) by agar dilution, MICs to VA and daptomycin (DAP) by E-test, and superantigenic toxin gene profiles by multiplex PCR. MRSA from septic arthritis patients were analyzed with population analysis and Triton-100 induced autolysis. Difference and correlations between genotypes and phenotypes of bacteremic MRSA isolates were determined by Fisher’s exact test and M-W-U test, respectively. Results: CA-MRSA (ST59-SCCmecIV-spa t437-dru9 without mutidrug resistance) harbored genotypes and phenotypes far from those of HA-MRSA (ST239-SCCmecIII-spa t037-dru14 with mutidrug resistance) in Taiwan. Totally 157 non-duplicate MRSA blood isolates with mecA were analyzed. Four major clones (ST239 or 241-SCCmecIII- spat037 or t421-agrI- dru12 or 14, ST59- SCCmecIV or VT-spat437-agrI- dru9 or 11, ST5-SCCmecII-spat002-agrII-dru4, and ST573- SCCmecIV-spat3406-agrII-dru9) were identified. pvl correlated with SCCmecVT, ST59, spat437, and dru11, while multidrug resistance (≥ 4 antimicrobials) with SCCmecIII, ST239, spat037, agrI, and dru14 (p < 0.001). Higher VA MIC was noted in SCCmecII and III; ST5, 239, and 241; spat002, t037, and t421; dru4, 10, 12, 13, and 14 (p < 0.05). No genotype correlated with MLSBi phenotype. Only 15 superantigenic toxin gene profiles were determined. Of these, 95 (60.5%) isolates possessed sea-selk-selq-SCCmecIII-agrI, 17 (7.6%) isolates with seb-selk-selq- SCCmecIV or VT-agrI or II, and 7 (4.5%) isolates only with sea. Conclusions: Genotypic and phenotypic differences existed between CA-MRSA and HA-MRSA. Limited clones with corresponding phenotypes were found in MRSA bloodstream isolates from Taiwan. Further attempts in typing consecutive strains are needed to delineate the epidemiology and the evolutionary changes of MRSA strains.
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