Journal of Antimicrobial Chemotherapy (2002) 49, 793-801
© 2002 The British Society for Antimicrobial Chemotherapy
Detection and expression of methicillin/oxacillin resistance in multidrug-resistant and non-multidrug-resistant Staphylococcus aureus in Central Sydney, Australia
1Department of Infectious Diseases, Faculty of Medicine, University of Sydney, 2006 New South Wales; 2Department of Microbiology and Infectious Diseases, Concord Repatriation General Hospital, Concord, Central Sydney Area Health Services, Hospital Road, 2139 New South Wales, Australia
Received 21 August 2001; returned 20 December 2001; revised 22 January 2002; accepted 4 February 2002.
Ninety clinical Staphylococcus aureus isolates from separate patients were examined phenotypically and genotypically for susceptibility to methicillin/oxacillin. Thirty were methicillin/oxacillin susceptible and 60 were methicillin and oxacillin resistant (MRSA). The 60 MRSA isolates examined were subdivided into two groups according to their antibiotic profiles and comprised 30 non-multidrug-resistant (NMDR) isolates, resistant to less than two non-ß-lactam antibiotics, and 30 multidrug-resistant (MDR) isolates, resistant to three or more non-ß-lactam antibiotics. Phenotypic and genotypic analysis of methicillin/oxacillin showed that despite use of the guidelines published by the NCCLS for the testing of S. aureus susceptibility to methicillin/oxacillin, MIC values of some NMDR MRSA isolates fell below the NCCLS-recommended breakpoints. Etest strips failed to detect two NMDR MRSA isolates tested with oxacillin and four tested with methicillin. Lowering the NCCLS-recommended oxacillin screen agar concentration from 6 to 2 mg/L and temperature of incubation to 30°C, improved the specificity and sensitivity of NMDR MRSA detection from 87% to 100%. On PFGE analysis these NMDR MRSA strains were genotypically different. Genotypic tests, such as multiplex PCR for the mecA/nuc genes and DNA hybridization for the mecA gene, or phenotypic monoclonal antibody-based tests to detect penicillin-binding protein 2a (PBP2a) offer advantages for problematic isolates in detecting or confirming low-level phenotypic heterogeneous mecA expression of oxacillin and methicillin resistance in NMDR MRSA.
* Correspondence address. Department of Infectious Diseases, Faculty of Medicine, DO6, Blackburn Building, University of Sydney, NSW 2006, Sydney, Australia. Tel: +61-2-9351-2412; Fax: +61-2-9351-4731; E-mail: JMerlino{at}med.usyd.edu.au or merlinoj{at}email.cs.nsw.gov.au
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  S. Bocher, R. Smyth, G. Kahlmeter, J. Kerremans, M. C. Vos, and R. Skov Evaluation of Four Selective Agars and Two Enrichment Broths in Screening for Methicillin-Resistant Staphylococcus aureus J. Clin. Microbiol., September 1, 2008; 46(9): 3136 - 3138. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. F. J. Brown, D. I. Edwards, P. M. Hawkey, D. Morrison, G. L. Ridgway, K. J. Towner, M. W. D. Wren, and on behalf of the Joint Working Party of the Britis Guidelines for the laboratory diagnosis and susceptibility testing of methicillin-resistant Staphylococcus aureus (MRSA) J. Antimicrob. Chemother., December 1, 2005; 56(6): 1000 - 1018. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. B. Gosbell, S. A. Neville, J. L. Mercer, L. A. Fernandes, and C. J. Fernandes Detection of intrinsic oxacillin resistance in non-multiresistant, oxacillin-resistant Staphylococcus aureus (NORSA) J. Antimicrob. Chemother., February 1, 2003; 51(2): 468 - 470. [Full Text] [PDF]
|
|