MRSA, Risistance, And Study Of Molecular Epidemiology In Staphylococcus Aureus

Objective To investigate the detection rate, drug-resistant rate and clinical distribution of methicillin resistente Staphylococcus aureus (MRSA) collected from certain hospital in three years (2007-2009) in order to enhance the clinical recognition of MRS A nosocomial infection and to provide laboratory evidence for reasonable selection of antibiotics in clinic. To analyse the homology of MRSA isolates in order to offer laboratory evidence for controlling infection and epidemic spread of drug-resistant strains.Methods (1) Nonrepetitive Staphylococcus aureus (SA) isolates were collected from Clinical Microbiology laboratory in a third class A hospital between January 2007 and December 2009. The clinical data of patients infected by SA were retrospectively analyzed. Antimicrobial susceptibility test was performed by disk diffusion method with penicillin(P);clindamycin(DA);erythromycin(E); Chloramphenicol(C); Azithromycin(AZM); gentamicin(CN); ciprofloxacin(CIP); Levofloxacin (LEV); teicoplanin(TEC); compound sulfamethoxazole (SXT); furadantin(F); Ampicillin/sulbactam(SAM); piperacillin/tazobactam (TZP); imipenem (IMP) and cefepime(FEP) disks. The antimicrobial susceptibility results were assessed according to the standands recommended by CLSI (2010).MRSA strains were screened by cefoxitin disk diffusion test and vancomycin MIC value of MRSA strains was detected by E-test strips.(2) MecA gene was amplified in strains selected by screening test in order to confirmed MRSA strains. (3) The SCCmec and spa genotyping of MRSA strains was perfonned as well as ERIC-PCR in order to analyse their homology. Results (1) Retrospective analysis result:The number of Staphylococcus aureus isolates was 34,97 and 103 from 2007 to 2009,respectively. Among the SA strains, there were 2,41 and 30 MRSA strains, respectively. And the detection rate of MRSA was 5.88%, 42.27% and 29.13%, respectively. The detection rate of MRSA in sputum samples was the highest,87.6%, followed by 2.7% in pleural fluid and secretion samples. Only two MRSA strains were detected in nephrology department and neurosurgery department in 2007.MRSA strains were detected successively in other wards in 2008 and 2009, with the highest detection rate in neurosurgery department,31.5%, followed by 17.8% in respiratory department. The drug-resistant rate of MRSA to P, E, DA, CA, CIP, LEV, IMP, SAM, TZP and FEP was higher than 90.0% in three years, and the drug-resistant rate to F and SXT was increasing. Vancomycin-resistant MRSA was not detected in our study. The vancomycin MIC value of MRSA strains was 0.5-2ug/ml. (2) Mec A gene detection result:Mec A gene was carried by 73 MRSA strains screened with cefoxitin disk diffusion test. The accordance rate of screening result and confirmation result was 100%.(3)SCCmec gene amplification result by multiple-PCR:All the 73 strains of MRSA harboured mec A gene with the amplification fragment of 147 base pairs, among them,71 strains also show an electrophoresis band with the amplification fragment of 280 base pairs, which belonged to SCCmec III genotype of MRSA. The other 2 MRSA isolates did not show other bands except mecA gene band, which belong to unknown types. (4) Spa typing result:72 strains of MRSA belonged to t030 spa type, which accounted for 98.6%, and 1 strain belonged to t304, which accounted for 1.4%. (5) ERIC-PCR typing result:Gel imaging of ERIC-PCR product showed 6 DNA fingerprint bands, including A type(66 strains), A'type(1 strain), B type(2 strains),C type(2 strain), D type(1 strain),and E type(1 type).The Similarity value of A and A'type was 88.9%(higher than 80%) analyzed by GENETOOLS map analysis software, which belonged to the same type. So, all the MRS A strains were divided into A,B,C,D,E 5 genotypes. (6) All the 23 strains of MRSA from neurosurgery were SCCmecⅢ-t030,A type. a small-scale outbreak infection of MRSA occurred in neurosurgery department in August of 2008.Conclusions (1) MRSA strains are mainly distributed in surgical department, and a small-scale outbreak infection of MRSA occurre in neurosurgery department, which belong to SCCmecⅢtype, spa t030 type, and ERIC-PCR A type, respectively, by homology analysis. MRSA strains have a high drug-resistant rate, but Vancomycin-resistant MRSA is not detected with MIC value between 0.5 and 2μg/ml.(2) MRSA strains in our study mainly belonged to SCCmecⅢtype, spa t030 type, and ERIC-PCR A type, and only 1 strain isolated in 2009 belonged to SCCmecⅢtype, spa t304 type, and ERIC-PCR E type.