| Objective: Methicillin-resistant Staphylococcus aureus (MRSA), a versatile human pathogen causing serious infections, is multi-resistant to a wide variety of antibiotics. In particular, MRSA is resistant to virtually all of the ?-lactams, and it thereby threatens the most potent antibiotics we have. This situation limits treatment options to a very few agents, such as vancomycin. However, in 1997 an MRSA clinical isolate that responded poorly to vancomycin therapy was reported in Japan. Five years later, in 2002, Isolation of vancomycin-resistant S. aureus with vancomycin mimimum inhibitory concentration (MIC>128 μg/ml) was documented in the United States. It is evident that the need to reconstruct our strategy of defenses against such pathogens is now urgent. The methicillin-resistance in Staphylococcus aureus is primarily due to the presence of the methicillin resistance determinant (mec) which intergrates into chromosomal segment number 10. In addition several other chromosomal factors unlinked to the mec determinant are essential for expression of methicillin resistance. such as the chromosomal femA,femB gene. In strains of these gene deletion,inactivation and mutant, We can watch decrease of methicillin-resistance expression. At present, No researches and reports about impact of femA femB to phenotypic resistance lead by gene mec in our country. The purpose of this study is to assess the necessary of MRSA auxiliary genes femA,femB and its correlations with resistance gene mecA through the study of correlation of the strains of gene femA,femB to gene resistance gene mecA and value of 13 antibiotics MIC,As a rule for choose antibiotics clinically. Method: From july in 2001 to October in 2003,81 SA strains were obtained. All clinical isolates from the second affiliated hospital , Dalian medical university. All strains were identified by the Bacto coagulase plasma test and API system estimated. MRSA are screened by Agar dilution method recommended by national committee for clinical lab standard (NCCLS) in 2003. A total of 81 strains staphylococcus aureus are analyzed for carriage of femA ,femB and mecA gene by duplex PCR amplification. The mecA gene positive MRSA are compared with those of the phenotypic susceptibility methods and oxacillin MIC. The antibacterial activity in vitro of 81 strains staphylococcus aureua to 13 antimicrobial agents is determined by agar dilution method, and the mecA gene positive SA, and mecA gene negative SA were contrasted. The effectiveness of femA ,femB to mecA was also assessed by 7 antibiotics MIC. Results: 81 strains staphylococcus aureus coagulase-negative test is positive. According to the Agar dilution method results ,The checked rate of MRSA is 56.8% . The mecA gene positive SA are 42 strains by duplex PCR. the checked rate of the mecA gene is 51.8%. The conformity of phenotypic methods genotypic analysis is 84.8%. In MRSA and MSSA strains, The checked of femA were 75 strains, femA-negative strains were 6 strains. The checked of femB were 74 strains, femB-negative strains were 7. Gene of femA femB distribute extensively from sensitivity,mediate-resistance to high-resistance strains. In mecA-positive strains, femA-positive strains are 38, femB-positive are 37,Gene femA,femB nagetive rate is 9.5%, 11.1% respectively. In mecA-negative strains, femA-positive strains is 37. femB-positive strains is 37, Gene femA , femB-negative checked rate is 5.1%, 5.1% respectively. No band gene of femA,femB was found in control Escherichia coli and Epidermis staphylococcus by duplex PCR amplification. Determinting MIC value of staphylococcus aureus of seven antibiotics by Agar dilution method. In mecA-negative strains, Value of MIC to seven antibiotics is the highest in femA,femB-positive strains. However value of MIC is higher than femA,femB-negative strains yet. In mecA –negative strains,value of MIC is to approach. In femA,femB-positive strains,mecA-positive strains value of MIC is higher than mecA-negative strains. It ha...
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