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Multicenter Evaluation of a Modified Cefoxitin Disk Diffusion Method and PBP2a Testing To Predict mecA-Mediated Oxacillin Resistance in Atypical Staphylococcus aureus.
J Clin Microbiol. 2017 02; 55(2):485-494.JC

Abstract

Phenotypic variants of Staphylococcus aureus that display small colonies, reduced pigmentation, and decreased hemolysis and/or coagulase activity are periodically isolated by the clinical laboratory. Antimicrobial susceptibility testing (AST) of these isolates is complicated, because many do not grow on routine AST media, including Mueller-Hinton agar (MHA) and cation-adjusted Mueller-Hinton broth. This multicenter study evaluated cefoxitin disk diffusion for 37 atypical S. aureus isolates (156 readings) with MHA supplemented with 5% sheep's blood (BMHA), using mecA PCR as the reference standard. The correlation of two commercial PBP2a assays with mecA PCR was also assessed. Ten isolates were negative and 27 positive for mecA No major errors for cefoxitin were observed, but 19.5% very major errors (VMEs) were observed at 24 h of incubation, and 17.2% VMEs were observed at 48 h. The proportions of VMEs ranged from 14.7 to 23.0% at 24 h, and from 13.3 to 17.6% at 48 h, across three testing laboratories. PBP2a tests were performed from growth on BMHA and blood agar plates (BAP), with and without cefoxitin disk induction. The Alere PBP2a SA culture colony test sensitivities for mecA were 90.0% with uninduced growth and 97.4% with induced growth from BMHA. On BAP, sensitivity was 96.0% with induced growth. The sensitivities of the Oxoid PBP2' latex agglutination test were 85.7% with uninduced growth and 93.9% with induced growth from BMHA and 95.9% with induced growth on BAP. On the basis of these data, we recommend that laboratories perform only mecA PCR and/or PBP2a tests when requested to perform AST on atypical isolates of S. aureus.

Authors+Show Affiliations

Department of Pathology and Laboratory Medicine, University of California-Los Angeles, Los Angeles, California, USA.Department of Laboratory Medicine, Cleveland Clinic, Cleveland, Ohio, USA.Division of Clinical Microbiology, Mayo Clinic, Rochester, Minnesota, USA.Division of Clinical Microbiology, Mayo Clinic, Rochester, Minnesota, USA.Department of Pathology and Laboratory Medicine, University of California-Los Angeles, Los Angeles, California, USA.Division of Clinical Microbiology, Mayo Clinic, Rochester, Minnesota, USA. Division of Infectious Diseases, Mayo Clinic, Rochester, Minnesota, USA.Department of Laboratory Medicine, Cleveland Clinic, Cleveland, Ohio, USA.Department of Pathology and Laboratory Medicine, University of California-Los Angeles, Los Angeles, California, USA rhumphries@mednet.ucla.edu.

Pub Type(s)

Evaluation Study
Journal Article
Multicenter Study

Language

eng

PubMed ID

27903603

Citation

Miller, Shelley A., et al. "Multicenter Evaluation of a Modified Cefoxitin Disk Diffusion Method and PBP2a Testing to Predict mecA-Mediated Oxacillin Resistance in Atypical Staphylococcus Aureus." Journal of Clinical Microbiology, vol. 55, no. 2, 2017, pp. 485-494.
Miller SA, Karichu J, Kohner P, et al. Multicenter Evaluation of a Modified Cefoxitin Disk Diffusion Method and PBP2a Testing To Predict mecA-Mediated Oxacillin Resistance in Atypical Staphylococcus aureus. J Clin Microbiol. 2017;55(2):485-494.
Miller, S. A., Karichu, J., Kohner, P., Cole, N., Hindler, J. A., Patel, R., Richter, S., & Humphries, R. M. (2017). Multicenter Evaluation of a Modified Cefoxitin Disk Diffusion Method and PBP2a Testing To Predict mecA-Mediated Oxacillin Resistance in Atypical Staphylococcus aureus. Journal of Clinical Microbiology, 55(2), 485-494. https://doi.org/10.1128/JCM.02211-16
Miller SA, et al. Multicenter Evaluation of a Modified Cefoxitin Disk Diffusion Method and PBP2a Testing to Predict mecA-Mediated Oxacillin Resistance in Atypical Staphylococcus Aureus. J Clin Microbiol. 2017;55(2):485-494. PubMed PMID: 27903603.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Multicenter Evaluation of a Modified Cefoxitin Disk Diffusion Method and PBP2a Testing To Predict mecA-Mediated Oxacillin Resistance in Atypical Staphylococcus aureus. AU - Miller,Shelley A, AU - Karichu,James, AU - Kohner,Peggy, AU - Cole,Nicolynn, AU - Hindler,Janet A, AU - Patel,Robin, AU - Richter,Sandra, AU - Humphries,Romney M, Y1 - 2016/11/30/ PY - 2016/11/02/received PY - 2016/11/22/accepted PY - 2016/12/3/pubmed PY - 2017/7/22/medline PY - 2016/12/2/entrez KW - Staphylococcus aureus KW - cefoxitin KW - mecA KW - small-colony variants KW - susceptibility testing SP - 485 EP - 494 JF - Journal of clinical microbiology JO - J. Clin. Microbiol. VL - 55 IS - 2 N2 - Phenotypic variants of Staphylococcus aureus that display small colonies, reduced pigmentation, and decreased hemolysis and/or coagulase activity are periodically isolated by the clinical laboratory. Antimicrobial susceptibility testing (AST) of these isolates is complicated, because many do not grow on routine AST media, including Mueller-Hinton agar (MHA) and cation-adjusted Mueller-Hinton broth. This multicenter study evaluated cefoxitin disk diffusion for 37 atypical S. aureus isolates (156 readings) with MHA supplemented with 5% sheep's blood (BMHA), using mecA PCR as the reference standard. The correlation of two commercial PBP2a assays with mecA PCR was also assessed. Ten isolates were negative and 27 positive for mecA No major errors for cefoxitin were observed, but 19.5% very major errors (VMEs) were observed at 24 h of incubation, and 17.2% VMEs were observed at 48 h. The proportions of VMEs ranged from 14.7 to 23.0% at 24 h, and from 13.3 to 17.6% at 48 h, across three testing laboratories. PBP2a tests were performed from growth on BMHA and blood agar plates (BAP), with and without cefoxitin disk induction. The Alere PBP2a SA culture colony test sensitivities for mecA were 90.0% with uninduced growth and 97.4% with induced growth from BMHA. On BAP, sensitivity was 96.0% with induced growth. The sensitivities of the Oxoid PBP2' latex agglutination test were 85.7% with uninduced growth and 93.9% with induced growth from BMHA and 95.9% with induced growth on BAP. On the basis of these data, we recommend that laboratories perform only mecA PCR and/or PBP2a tests when requested to perform AST on atypical isolates of S. aureus. SN - 1098-660X UR - https://www.unboundmedicine.com/medline/citation/27903603/Multicenter_Evaluation_of_a_Modified_Cefoxitin_Disk_Diffusion_Method_and_PBP2a_Testing_To_Predict_mecA_Mediated_Oxacillin_Resistance_in_Atypical_Staphylococcus_aureus_ L2 - http://jcm.asm.org/cgi/pmidlookup?view=long&pmid=27903603 DB - PRIME DP - Unbound Medicine ER -