title: [A study on the mechanism of drug resistance in Staphylococcus aureus].
abstract: OBJECTIVE
  To inquire into the mechanism of drug resistance in Staphylococcus aureus.
  
  
  METHODS
  A total of 198 strains of Staphylococcus aureus were isolated from the samples sent to the Clinical Laboratory of Microbiology,West China Hospital. The resistance of Staphylococcus aureus to Methicillin was assayed with agar dilution. Staphylococcus aureus mecA gene was measured by PCR assay and beta-lactamase was detected by Nitrocephin.
  
  
  RESULTS
  The rate of resistance to methicillin was 64.65% in 198 strains of Staphylococcus aureus; 118 strains of methicillin-resistant staphylococcus aureus(MRSA) were found to have high level resistance in 128 MRSA;10 strains of MRSA were found to have low level resistance; 41(58.57%) strains of methicillin-sensitive Staphylococcus aureus (MSSA) expressed beta-lactamase; 2 Staphylococcus aureus had mecA among them; 67 Staphylococcus aureus expressed beta-lactamase in high level resistance, 63(53.39%)Staphylococcus aureus expressed beta-lactamase in high level resistance, among them, 5 Staphylococcus aureus had mecA; 40.00% MRSA expressed beta-lactamase in low level resistance, 55 MRSA did not express beta-lactamase in high level resistance, which had all mecA; 9 Staphylococcus aureus did not express beta-lactamase in low level resistance, among them, 5 Staphylococcus aureus had mecA. The difference in expression of beta-lactamase was statistically significant between MSSA and MRSA; MRSA(53.39%) was lower than MSSA (58.57%); the other differences were not significant. The difference in having mecA was statistically significant between MRSA(having high resistant level and no expression of beta-lactamase) and the others; MRSA had higher mecA than did the others.
  
  
  CONCLUSIONS
  The resistance in Staphylococcus aureus mainly involved two mechanisms: the expression of beta-lactamase and the expression of mecA.
authors.affiliation: Department of Infectious Diseases, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu 610041, China.
authors.forename: Xiao-fang
authors.initials: XF
authors.lastname: Li
authors.forename: Xin-jian
authors.initials: XJ
authors.lastname: Fan
authors.forename: Xiao-Jing
authors.initials: XJ
authors.lastname: Guo
authors.forename: Peng
authors.initials: P
authors.lastname: Feng
authors.forename: Xiao-ju
authors.initials: XJ
authors.lastname: Lü
authors.forename: Yan-Yu
authors.initials: YY
authors.lastname: Gao
authors.forename: Ya-Li
authors.initials: YL
authors.lastname: Xiong
authors.forename: Ru-Jia
authors.initials: RJ
authors.lastname: Yu
authors.forename: Xia
authors.initials: X
authors.lastname: Ding
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D002681:China; D005798:Genes, Bacterial / Q000235:genetics; D006801:Humans; D016106:Methicillin Resistance / Q000235:genetics*; D046915:Penicillin-Binding Proteins; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus; D001618:beta-Lactamases