The effect of interlaboratory variability on antimicrobial susceptibility determination

Annis, David H.; Craig, Bruce A.

doi:10.1016/j.diagmicrobio.2005.03.012

Cited by 16 publications

(14 citation statements)

References 3 publications

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“…AST results are assigned to one of three categories (susceptible, intermediate, or resistant) based on two critical lower and upper MIC breakpoints. The susceptible and resistant classes are commonly separated by an intermediate class corresponding to just one twofold dilution (Annis and Craig, 2005). Given the narrowness of this intermediate range, such a factor of variability can seriously impact the correct classification of a pathogen if its MIC is near the breakpoints (Craig, 2000).…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, a MIC value is not a simple concentration, unlike the value measured by HPLC, and actually represents the overall effect obtained over the entire incubation time. Repeated measurements of MIC using the same pathogen/drug combination commonly show a 3-fold dilution range, meaning that the standard microdilution method has an accuracy of not less than one dilution interval and that a one dilution difference can be considered as acceptable (Wexler et al, 1990; Annis and Craig, 2005). …”

Section: Discussionmentioning

confidence: 99%

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In vitro Degradation of Antimicrobials during Use of Broth Microdilution Method Can Increase the Measured Minimal Inhibitory and Minimal Bactericidal Concentrations

et al. 2016

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The antibacterial activity of some antimicrobials may be under-estimated during in vitro microbiological susceptibility tests, due to their instability under such conditions. The in vitro degradation of seven widely used antimicrobials (amoxicillin, cephalexin monohydrate, cefotaxime sodium salt, ciprofloxacin, erythromycin hydrate, clarithromycin, and doxycycline hyclate) and its effect on MIC and MBC determinations was studied using the broth microdilution method, considered as the gold standard for MIC determinations. In vitro concentrations of antimicrobials, over a 24 h incubation period in the medium tested without bacteria, decreased from 33% for ciprofloxacin to 69% for clarithromycin. For cephalexin, cefotaxime, clarithromycin, and doxycycline which were the most degraded drugs, MIC and MBC values for one strain of E. coli and one strain of S. aureus were compared using the standard method or after ad-hoc drug complementation aiming at maintaining constant drug concentration. Abiotic degradation during the standard method was associated with a significant increase of the MIC (2 antibiotics) and MBC (3 antibiotics). However, the observed discrepancy (less than one twofold dilution), even for the most degraded drug for which the concentration at 24 h was reduced by two thirds, suggests that this would only be clinically significant in special cases such as slow-growing bacteria.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

In vitro Degradation of Antimicrobials during Use of Broth Microdilution Method Can Increase the Measured Minimal Inhibitory and Minimal Bactericidal Concentrations

et al. 2016

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“…Past studies have shown that the measurement error distribution for the MIC and DIA is both Normal and we will assume this here. Thus, given m i , the probability we observe x i is

Φ (x_{i}; m_{i}, σ_{m}^{2}) - Φ (x_{i} - 1; m_{i}, σ_{m}^{2}),

where Φ is the standard Normal CDF.…”

Section: Methodsmentioning

confidence: 99%

“…For each scenario, the measurement error standard deviations used for the MIC and DIA assays were set at 0.707 and 2.121, respectively, on the basis of an abundance of quality control data. 1,6 We used 2 sets of MIC breakpoints per scenario to evaluate DIA breakpoint performance. The number of pathogens was set at 1000, and we consider 200 scatterplots.…”

Section: Simulation Detailsmentioning

confidence: 99%

Bayesian monotonic errors‐in‐variables models with applications to pathogen susceptibility testing

DePalma

Craig

2017

Statistics in Medicine

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Drug dilution (MIC) and disk diffusion (DIA) are the 2 most common antimicrobial susceptibility assays used by hospitals and clinics to determine an unknown pathogen's susceptibility to various antibiotics. Since only one assay is commonly used, it is important that the 2 assays give similar results. Calibration of the DIA assay to the MIC assay is typically done using the error-rate bounded method, which selects DIA breakpoints that minimize the observed discrepancies between the 2 assays. In 2000, Craig proposed a model-based approach that specifically models the measurement error and rounding processes of each assay, the underlying pathogen distribution, and the true monotonic relationship between the 2 assays. The 2 assays are then calibrated by focusing on matching the probabilities of correct classification (susceptible, indeterminant, and resistant). This approach results in greater precision and accuracy for estimating DIA breakpoints. In this paper, we expand the flexibility of the model-based method by introducing a Bayesian 4-parameter logistic model (extending Craig's original 3-parameter model) as well as a Bayesian nonparametric spline model to describe the relationship between the 2 assays. We propose 2 ways to handle spline knot selection, considering many equally spaced knots but restricting overfitting via a random walk prior and treating the number and location of knots as additional unknown parameters. We demonstrate the 2 approaches via a series of simulation studies and apply the methods to 2 real data sets.

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“…This result is within the range determined by broth microdilution, the gold standard method (8-16 µg/mL). Despite difficulties in variability of measuring MICs, [22,23] these values are used by clinicians when making decisions about patient care (antibiotic selection and dosing), and hence are an important result for any new diagnostic tool to accurately measure.…”

Section: Mainmentioning

confidence: 99%

Cantilever Sensors for Rapid Optical Antimicrobial Sensitivity Testing

Bennett

Pyne

McKendry

2019

Preprint

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Growing antimicrobial resistance (AMR) is a serious global threat to human health. Current methods to detect resistance include phenotypic antibiotic sensitivity testing (AST) which measures bacterial growth and is therefore hampered by slow time to result (~12-24 hours).Therefore new rapid phenotypic methods for AST are urgently needed. Nanomechanical cantilever sensors have recently shown promise for rapid AST but challenges of bacterial immobilization can lead to variable results. Herein a novel cantilever-based method is described for detecting phenotypic antibiotic resistance within ~45 minutes, capable of detecting single bacteria. This method does not require complex, variable bacterial immobilization, and instead uses the laser and detector system to detect single bacterial cells in media as they pass through the laser focus. This provides a simple read out of bacterial antibiotic resistance by detecting growth (resistant) or death (sensitive), much faster than

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The effect of interlaboratory variability on antimicrobial susceptibility determination

Cited by 16 publications

References 3 publications

In vitro Degradation of Antimicrobials during Use of Broth Microdilution Method Can Increase the Measured Minimal Inhibitory and Minimal Bactericidal Concentrations

In vitro Degradation of Antimicrobials during Use of Broth Microdilution Method Can Increase the Measured Minimal Inhibitory and Minimal Bactericidal Concentrations

Bayesian monotonic errors‐in‐variables models with applications to pathogen susceptibility testing

Cantilever Sensors for Rapid Optical Antimicrobial Sensitivity Testing

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