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Optimizing the detection of methicillin-resistant Staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range

BACKGROUND: Determination of vancomycin minimum inhibitory concentration (MIC) can influence the agent used to treat methicillin-resistant Staphylococcus aureus (MRSA) infection. We studied diagnostic accuracy using E-test and VITEK(®) 2 against a gold standard broth microdilution (BMD) methodology,...

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Autores principales: Phillips, Cameron J, Wells, Nicholas A, Martinello, Marianne, Smith, Simon, Woodman, Richard J, Gordon, David L
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Dove Medical Press 2016
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4898034/
https://www.ncbi.nlm.nih.gov/pubmed/27330319
http://dx.doi.org/10.2147/IDR.S107961
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author Phillips, Cameron J
Wells, Nicholas A
Martinello, Marianne
Smith, Simon
Woodman, Richard J
Gordon, David L
author_facet Phillips, Cameron J
Wells, Nicholas A
Martinello, Marianne
Smith, Simon
Woodman, Richard J
Gordon, David L
author_sort Phillips, Cameron J
collection PubMed
description BACKGROUND: Determination of vancomycin minimum inhibitory concentration (MIC) can influence the agent used to treat methicillin-resistant Staphylococcus aureus (MRSA) infection. We studied diagnostic accuracy using E-test and VITEK(®) 2 against a gold standard broth microdilution (BMD) methodology, the correlation between methods, and associations between vancomycin MIC and MRSA phenotype from clinical isolates. METHODS: MRSA isolates were obtained from April 2012 to December 2013. Vancomycin MIC values were determined prospectively on all isolates by gradient diffusion E-test and automated VITEK(®) 2. The Clinical and Laboratory Standards Institute reference BMD method was performed retrospectively on thawed frozen isolates. Diagnostic accuracy for detecting less susceptible strains was calculated at each MIC cutoff point for E-Test and VITEK(®) 2 using BMD ≥1 µg/mL as a standard. The correlation between methods was assessed using Spearman’s rho (ρ). The association between MRSA phenotype and MIC for the three methods was assessed using Fisher’s exact test. RESULTS: Of 148 MRSA isolates, all except one (E-test =3 µg/mL) were susceptible to vancomycin (MIC of ≤2 µg/mL) irrespective of methodology. MICs were ≥1.0 µg/mL for 9.5% of BMD, 50.0% for VITEK(®) 2, and 27.7% for E-test. Spearman’s ρ showed weak correlations between methods: 0.29 E-test vs VITEK(®) 2 (P=0.003), 0.27 E-test vs BMD (P=0.001), and 0.31 VITEK(®) 2 vs BMD (P=0.002). The optimal cutoff points for detecting BMD-defined less susceptible strains were ≥1.0 µg/mL for E-test and VITEK(®) 2. E-test sensitivity at this cutoff point was 0.85 and specificity 0.29, while VITEK(®) 2 sensitivity and specificity were 0.62 and 0.51, respectively. Multiresistant MRSA strains tended to have higher MIC values compared to nonmultiresistant MRSA or epidemic MRSA 15 phenotypes by E-test (Fisher’s exact P<0.001) and VITEK(®) 2 (Fisher’s exact P<0.001). CONCLUSION: Overall diagnostic accuracy and correlations between MIC methods used in routine diagnostic laboratories and the gold standard BMD showed limited overall agreement. This study helps optimize guidance on the effective use of vancomycin.
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spelling pubmed-48980342016-06-21 Optimizing the detection of methicillin-resistant Staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range Phillips, Cameron J Wells, Nicholas A Martinello, Marianne Smith, Simon Woodman, Richard J Gordon, David L Infect Drug Resist Original Research BACKGROUND: Determination of vancomycin minimum inhibitory concentration (MIC) can influence the agent used to treat methicillin-resistant Staphylococcus aureus (MRSA) infection. We studied diagnostic accuracy using E-test and VITEK(®) 2 against a gold standard broth microdilution (BMD) methodology, the correlation between methods, and associations between vancomycin MIC and MRSA phenotype from clinical isolates. METHODS: MRSA isolates were obtained from April 2012 to December 2013. Vancomycin MIC values were determined prospectively on all isolates by gradient diffusion E-test and automated VITEK(®) 2. The Clinical and Laboratory Standards Institute reference BMD method was performed retrospectively on thawed frozen isolates. Diagnostic accuracy for detecting less susceptible strains was calculated at each MIC cutoff point for E-Test and VITEK(®) 2 using BMD ≥1 µg/mL as a standard. The correlation between methods was assessed using Spearman’s rho (ρ). The association between MRSA phenotype and MIC for the three methods was assessed using Fisher’s exact test. RESULTS: Of 148 MRSA isolates, all except one (E-test =3 µg/mL) were susceptible to vancomycin (MIC of ≤2 µg/mL) irrespective of methodology. MICs were ≥1.0 µg/mL for 9.5% of BMD, 50.0% for VITEK(®) 2, and 27.7% for E-test. Spearman’s ρ showed weak correlations between methods: 0.29 E-test vs VITEK(®) 2 (P=0.003), 0.27 E-test vs BMD (P=0.001), and 0.31 VITEK(®) 2 vs BMD (P=0.002). The optimal cutoff points for detecting BMD-defined less susceptible strains were ≥1.0 µg/mL for E-test and VITEK(®) 2. E-test sensitivity at this cutoff point was 0.85 and specificity 0.29, while VITEK(®) 2 sensitivity and specificity were 0.62 and 0.51, respectively. Multiresistant MRSA strains tended to have higher MIC values compared to nonmultiresistant MRSA or epidemic MRSA 15 phenotypes by E-test (Fisher’s exact P<0.001) and VITEK(®) 2 (Fisher’s exact P<0.001). CONCLUSION: Overall diagnostic accuracy and correlations between MIC methods used in routine diagnostic laboratories and the gold standard BMD showed limited overall agreement. This study helps optimize guidance on the effective use of vancomycin. Dove Medical Press 2016-05-31 /pmc/articles/PMC4898034/ /pubmed/27330319 http://dx.doi.org/10.2147/IDR.S107961 Text en © 2016 Phillips et al. This work is published and licensed by Dove Medical Press Limited The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License (http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.
spellingShingle Original Research
Phillips, Cameron J
Wells, Nicholas A
Martinello, Marianne
Smith, Simon
Woodman, Richard J
Gordon, David L
Optimizing the detection of methicillin-resistant Staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range
title Optimizing the detection of methicillin-resistant Staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range
title_full Optimizing the detection of methicillin-resistant Staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range
title_fullStr Optimizing the detection of methicillin-resistant Staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range
title_full_unstemmed Optimizing the detection of methicillin-resistant Staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range
title_short Optimizing the detection of methicillin-resistant Staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range
title_sort optimizing the detection of methicillin-resistant staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range
topic Original Research
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4898034/
https://www.ncbi.nlm.nih.gov/pubmed/27330319
http://dx.doi.org/10.2147/IDR.S107961
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