Performance of Eight Methods, Including Two New Rapid Methods, for Detection of Oxacillin Resistance in a Challenge Set ofStaphylococcus aureus Organisms

ABSTRACT Using a set of 55 Staphylococcus aureus challenge organisms, we evaluated six routine methods (broth microdilution, disk diffusion, oxacillin agar screen, MicroScan conventional panels, MicroScan rapid panels, and Vitek cards) currently used in many clinical laboratories and two new rapid methods, Velogene and the MRSA-Screen, that require less than a day to determine the susceptibility of S. aureus to oxacillin. The methods were evaluated by using the presence of the mecAgene, as detected by PCR, as the “gold standard.” The strains included 19 mecA-positive heterogeneously resistant strains of expression class 1 or 2 (demonstrating oxacillin MICs of 4 to >16 μg/ml) and 36 mecA-negative strains. The oxacillin MICs of the latter strains were 0.25 to 4 μg/ml when tested by broth microdilution with 2% NaCl-supplemented cation-adjusted Mueller-Hinton broth as specified by the NCCLS. However, when tested by agar dilution with 4% salt (the conditions used in the oxacillin agar screen method), the oxacillin MICs of 16 of themecA-negative strains increased to 4 to 8 μg/ml. On initial testing, the percentages of correct results (% sensitivity/% specificity) were as follows: broth microdilution, 100/100; Velogene, 100/100; Vitek, 95/97; oxacillin agar screen, 90/92; disk diffusion, 100/89; MicroScan rapid panels, 90/86; MRSA-Screen, 90/100; and MicroScan conventional, 74/97. The MRSA-Screen sensitivity improved to 100% if agglutination reactions were read at 15 min. Repeat testing improved the performance of some but not all of the systems.

[1]  M. Ferraro,et al.  Optimal Inoculation Methods and Quality Control for the NCCLS Oxacillin Agar Screen Test for Detection of Oxacillin Resistance in Staphylococcus aureus , 2001, Journal of Clinical Microbiology.

[2]  Ronald N. Jones,et al.  Comparison of the Vitek Gram-Positive Susceptibility 106 Card and the MRSA-Screen Latex Agglutination Test for Determining Oxacillin Resistance in Clinical Bloodstream Isolates of Staphylococcus aureus , 2001, Journal of Clinical Microbiology.

[3]  M. Louie,et al.  Evaluation of Three Rapid Methods for Detection of Methicillin Resistance in Staphylococcus aureus , 2000, Journal of Clinical Microbiology.

[4]  S. C. Sanyal,et al.  Rapid detection of methicillin resistance in staphylococci using a slide latex agglutination kit. , 2000, International journal of antimicrobial agents.

[5]  C. Bantar,et al.  Comparison of several methods to determine methicillin-resistance in Staphylococcus aureus with focus on borderline strains. , 2000, Diagnostic microbiology and infectious disease.

[6]  G. Woods,et al.  Evaluation of a latex agglutination assay for rapid detection of oxacillin resistant Staphylococcus aureus. , 2000, Diagnostic microbiology and infectious disease.

[7]  Mary Jane Ferraro,et al.  Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically : approved standard , 2000 .

[8]  Ronald N. Jones,et al.  Methods for Improved Detection of Oxacillin Resistance in Coagulase-Negative Staphylococci: Results of a Multicenter Study , 1999, Journal of Clinical Microbiology.

[9]  D. Persing,et al.  Comparison of Susceptibility Testing Methods withmecA Gene Analysis for Determining Oxacillin (Methicillin) Resistance in Clinical Isolates of Staphylococcus aureus and Coagulase-Negative Staphylococcus spp , 1999, Journal of Clinical Microbiology.

[10]  H. Verbrugh,et al.  Rapid Detection of Methicillin Resistance in Staphylococcus aureus Isolates by the MRSA-Screen Latex Agglutination Test , 1999, Journal of Clinical Microbiology.

[11]  A. Buiting,et al.  Rapid Slide Latex Agglutination Test for Detection of Methicillin Resistance in Staphylococcus aureus , 1999, Journal of Clinical Microbiology.

[12]  M. Cavassini,et al.  Evaluation of MRSA-Screen, a Simple Anti-PBP 2a Slide Latex Agglutination Kit, for Rapid Detection of Methicillin Resistance in Staphylococcus aureus , 1999, Journal of Clinical Microbiology.

[13]  J. Boyce,et al.  Misclassification of Susceptible Strains ofStaphylococcus aureus as Methicillin-Resistant S. aureus by a Rapid Automated Susceptibility Testing System , 1999, Journal of Clinical Microbiology.

[14]  R. Skov,et al.  Evaluation of a new 3-h hybridization method for detecting the mecA gene in Staphylococcus aureus and comparison with existing genotypic and phenotypic susceptibility testing methods. , 1999, The Journal of antimicrobial chemotherapy.

[15]  N. Frebourg,et al.  Comparison of ATB Staph, Rapid ATB Staph, Vitek, and E-Test Methods for Detection of Oxacillin Heteroresistance in Staphylococci Possessing mecA , 1998, Journal of Clinical Microbiology.

[16]  C. Resende,et al.  Discrimination of methicillin-resistant Staphylococcus aureus from borderline-resistant and susceptible isolates by different methods. , 1997, Journal of medical microbiology.

[17]  D. Farrell The reliability of Microscan™ conventional and rapid panels to identify Staphylococcus aureus and detect methicillin resistance: An evaluation using the tube coagulase test and mecA PCR , 1997, Pathology.

[18]  J A Washington,et al.  Evaluation of Vitek GPS-SA card for testing of oxacillin against borderline-susceptible staphylococci that lack mec , 1996, Journal of clinical microbiology.

[19]  J A Washington,et al.  Evaluation of differential inoculum disk diffusion method and Vitek GPS-SA card for detection of oxacillin-resistant staphylococci , 1994, Journal of clinical microbiology.

[20]  G. Eliopoulos,et al.  Comparison of tests for detection of methicillin-resistant Staphylococcus aureus in a clinical microbiology laboratory , 1994, Antimicrobial Agents and Chemotherapy.

[21]  F. Tenover,et al.  Two percent sodium chloride is required for susceptibility testing of staphylococci with oxacillin when using agar-based dilution methods , 1993, Journal of clinical microbiology.

[22]  O. Brakstad,et al.  Multiplex polymerase chain reaction for detection of genes for Staphylococcus aureus thermonuclease and methicillin resistance and correlation with oxacillin resistance , 1993, APMIS : acta pathologica, microbiologica, et immunologica Scandinavica.

[23]  H. Uchida,et al.  Assessment of oxacillin salt agar for detection of MRSA identified by presence of the mecA gene. , 1993, The Journal of hospital infection.

[24]  D E Low,et al.  Evaluation of commercial and standard methodology for determination of oxacillin susceptibility in Staphylococcus aureus , 1992, Journal of clinical microbiology.

[25]  J. Gerberding,et al.  Comparison of conventional susceptibility tests with direct detection of penicillin-binding protein 2a in borderline oxacillin-resistant strains of Staphylococcus aureus , 1991, Antimicrobial Agents and Chemotherapy.

[26]  J. Waitz Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically , 1990 .

[27]  A. Tomasz,et al.  New mechanism for methicillin resistance in Staphylococcus aureus: clinical isolates that lack the PBP 2a gene and contain normal penicillin-binding proteins with modified penicillin-binding capacity , 1989, Antimicrobial Agents and Chemotherapy.