| Staphylococcus aureus (S. aureus) are common organism causing wide variety of infection, ranging from minor skin infection, food poisoning, staphylococcal scalded skin syndrome, toxic shock syndrome, artificial device-related infection, urinary tract infections, arthritis to fatal infections such as sepsis, endocarditis, pericarditis, pneumonia, etc. From the last centry, infections caused by staphylococcus aureus, especially methicilin-resistant staphylococcus aureus (MRSA) endangered human health seriously. A thorough understanding of the molecular epidemiology and evolution of MRSA is important for designing proper intervention strategies and infection control measures to prevent the spread and continued emergence of MRSA strains.PART ONE Antimicrobial resistance of MRSAObject:To understand the resistance character of MRSA strains. Method:1. A totle of 154 staphylococcus aureus were sampled from blood, sputum, excreta, drainage fluid, pus, etc. from three level of first-class hospital in Tianjin. There were 75 methicilin-sensitive S. aureus (MSSA) strains and 79 MRSA strains; Identification of S. aureus was by VITEK automatic system and a latex agglutination test. mecA gene was detected by polymerase chain reaction (PCR).2. Antimicrobial susceptibility of penicillin, oxacillin, ampicillin, ciprofloxacin, moxifloxacin, cefazolin, chloramphenicol, lincomycin, gentamycin, ceftriaxone, erythromycin, Rifampicin, tetracycline, vancomycin, teicoplanin, sulfamethoxazole complex, linezolid, tigecycline was determined by microdilution broth method or Kirby-Bauer method.3. Inducible clindamycin resistance was identified as a D-shaped inhibition zone by the clindamycin-erythromycin double-disk test. Result:79 MRSA strains had high resistant rate to vary kind of antibiotics, but the resistant rate to chloramphenicol and sulfamethoxazole-trimethoprim were relatively lower (3.80%,10.13%) respectively. All of the testing strains were susceptible to glycopeptide antibiotics, linezolid, tigecycline.7 strains were D-zone test positive. Conclusions: MRSA isolated from clinic source were multi-drug resistant strains. Inducible clindamycin resistance was found in erythromycin-resistant and clindamycin- sensitive strains.PART TWO Genotyping of SCCmec in 79 MRSA isolatesObject:To understand the SCCmec genotypes of MRSA isolated from a teaching hospital of Tianjin. Method:SCCmec typing:9 pairs of primers designed according to the sequence which were selected from the region specific to SCCmec typeâ… -â…¤respectively. Multiplex PCR was used for amplificating SCCmec element. Result:All of the 79 MRSA harboured SCCmec typeâ…¢. Besides the PCR amplified bands specified for SCCmec typeâ…¢, all of the strains added 495bp,449bp bands and 83.54%(66/79)added 342bp band as well. Conclusion:All of the MRSA isolated from a hospital in Tianjin contained SCCmec typeâ…¢.PART THREE Strain-relatedness of Staphylococcus aureus recoverd from patients with multiplex sites infectionObject:To understand the strain-relatedness of MRSA recoverd from multiplex sites infection with the same patient. Method:11 strains isolated from 5 patients with S. aureus infection:blood/sputum/secretion, blood/troat swab, blood/sputum, blood/ sputum, blood/sputum.2. Pulsed Field Gel Electrophoresis(PFGE) analysis:The S. aureus were genotyped by PFGE with Smaâ… -digested chromosomal DNA. Result: PFGE pattern revealed that 4 pairs of S. aureus from 4 patients respectively had the same number of bands and the corresponding bands are the same apparent size. The S. aureus recovered from secretion had more than 7 bands differences with from blood and sputum within one patient. Conclusion:Multiplex sites infection almost caused by the same strain within one patient.
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