Comparison of 30 μg and 120 μg gentamicin disks for the prediction of gentamicin resistance in <i>Enterococcus faecalis</i>

Kronvall, Göran; Ringertz, Signe; NystrÖM, Siv; Rylander, Margareta; Theodorsson, Elvar

doi:10.1111/j.1699-0463.1991.tb01275.x

Cited by 12 publications

(12 citation statements)

References 20 publications

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“…First, the exact figure from NRI calculations is rounded up, thereby including more isolates. Second, an analysis of the WT peak in an inhibition zone diameter histogram showed that the WT population was slightly peaked and skewed toward higher zone values (13). This would also apply to MIC distributions, although the precision is lower compared to disc diffusion tests.…”

Section: Discussionmentioning

confidence: 99%

Normalized Resistance Interpretation as a Tool for Establishing Epidemiological MIC Susceptibility Breakpoints

Kronvall

2010

J Clin Microbiol

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Normalized resistance interpretation (NRI) utilizes the fact that the wild-type population on the sensitive side is not affected by resistance development, and therefore a normalized reconstruction of the peak can be performed Traditional concepts for setting interpretive breakpoints in antimicrobial susceptibility testing were challenged by J. D. Williams in 1990 when he proposed the setting of so-called microbiological guidelines in relation to the distribution of inhibition zone diameter values (or MIC values) of the susceptible population, for instance two standard deviations (SD) below the mode inhibition zone size (24). This would require a species-related aspect which was not yet accepted, although some reports on this issue had been published (2,12,14). Earlier, O'Brien had shown that an adjustment of interpretive breakpoints in relation to the susceptible peak in zone diameter histograms made results from different laboratories comparable and thereby foresaw later developments (17). In recent years, the term epidemiological breakpoints or epidemiological cutoff (ECOFF), has been proposed by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) to describe the upper MIC limit of the susceptible peak in an MIC distribution, the wild-type (WT) population. MIC distributions of WT isolates species-wise for many antimicrobials have been published on the internet by EUCAST and are publicly available (http://www.eucast.org/mic_distributions/) (5, 6).Normalized resistance interpretation (NRI) is an objective method to define the WT population in inhibition zone diameter histograms (4,8,10). The method has been used for setting interpretive breakpoints in an 18-year resistance surveillance, and also in an investigation of meropenem susceptibility in Pseudomonas aeruginosa (3,22). It was recently used extensively in marine microbiology by P. . NRI was also used successfully to analyze Etest MIC data to set epidemiological breakpoints for tigecycline (11). However, a direct application of NRI to regular 2-fold dilution MIC results has not been possible because the mathematical calculations will be based on too few data points. The use of NRI has been extended in the present investigations to regular MIC values by the introduction of helper variables, and NRI has been evaluated as a method for the objective estimation of epidemiological breakpoints using the EUCAST MIC distributions as the material and as the reference (http://www.eucast .org/mic_distributions/). MATERIALS AND METHODSMIC distributions. The publicly available EUCAST MIC distributions include a large number of bacterial species and antimicrobials (http://www.eucast.org /mic_distributions/). For the purpose of testing the NRI method for MIC distributions in the present studies, results for Staphylococcus aureus and Escherichia coli were used. EUCAST claim on their website that the "Histograms display WT organisms." It is not clear, however, which method is used to ensure this selection in the published materials, which can include as ...

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Section: Discussionmentioning

confidence: 99%

Normalized Resistance Interpretation as a Tool for Establishing Epidemiological MIC Susceptibility Breakpoints

Kronvall

2010

J Clin Microbiol

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“…This corresponds rather well to the distribution of susceptible isolates, the WT population. Such a distribution was analysed regarding conformity with a normal distribution and was found to fit well, except being slightly peaked and with a kurtosis towards higher zone values [41]. In fact, a WT…”

Section: Estimation Of Wild-type Populations and Cut-off Valuesmentioning

confidence: 94%

“…SRA can be done in individual laboratories where interlaboratory variation otherwise would have resulted in erroneous interpretations. The SRA method has been applied to several combinations of antimicrobials and species [15,[37][38][39][40][41][42][43][44]. A simple explanation of SRA with a review was published in 1991 [45].…”

Section: Page 10 Of 38mentioning

confidence: 99%

“…Other applications of SRA for testing disk contents were tried in Sweden and in Estonia on fusidic acid testing of S. aureus and the setting of breakpoints for use in Estonia [49]. An analysis on Iso-Sensitest Agar of various disk contents on gentamicin susceptibility testing of E. faecalis showed that a 30 g disk could separate highly resistant strains from low-level resistant strains, thereby making an extra test using a 120 g disk unnecessary [41]. In Sweden and some other countries, the standard gentamicin disk content is 30 g, whereas the NCCLS/Clinical and Laboratory Standards Institute (CLSI) recommends a 10 g gentamicin disk for species other than enterococci.…”

Section: Page 10 Of 38mentioning

confidence: 99%

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Setting interpretive breakpoints for antimicrobial susceptibility testing using disk diffusion

Kronvall

Giske

Kahlmeter

2011

International Journal of Antimicrobial Agents

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Antimicrobial susceptibility testing plays a key role in clinical microbiology. The disk diffusion test dates back to the 1940s and became standardised from the 1950s, with the International Collaborative Study (ICS) and National Committee for Clinical Laboratory Standards (NCCLS) as the two major standards. Interlaboratory variation of disk test results was recognised early but has never been dealt with in a satisfactory manner. The error-rate bounded method was described in 1974 and its role is discussed. Species-specific susceptibility interpretation was coined in 1980 for Proteus mirabilis and chloramphenicol. In the late 1970s, more extensive use of species-specific breakpoints was introduced in Lund (Sweden). At the same time, P.Mouton constructed species-specific regression lines and pointed out the difficulties with narrow ranges of minimal inhibitory concentration (MIC) values. A more general use of species-specific regression lines was made possible with single-strain regression analysis, using one well-defined strain tested in disk diffusion with a range of disk contents. This method made it possible to calibrate the disk test in an individual laboratory. Other methods to achieve such calibration are also described.A recent method, ‗MIC-coloured zone diameter histogram-technique', has proven useful for the validation of species-specific interpretive breakpoints. The microbiological breakpoint proposed by Williams in 1990 has experienced a renaissance with the European Committee on Antimicrobial Susceptibility Testing (EUCAST) epidemiological cut-off value (ECOFF). MIC and zone diameter distributions with accompanying ECOFFs for species-antimicrobial combinations are published on the EUCAST website. A method for the reconstruction of wild-type zone diameter populations, namely normalised resistance interpretation, is described. This

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“…Parametric statistical measures, such as the mean and standard deviation (S.D. ), have been shown earlier to describe zone diameter histogram populations accurately [32]. The susceptible population is thereby defined and a lower limit for susceptibility can be set to any value of the S.D.…”

Section: Nrimentioning

confidence: 99%

Extended antimicrobial resistance screening of the dominant faecal Escherichia coli and of rare resistant clones

Kronvall¹,

Larsson²,

Borén³

et al. 2005

International Journal of Antimicrobial Agents

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Comparison of 30 μg and 120 μg gentamicin disks for the prediction of gentamicin resistance in Enterococcus faecalis

Cited by 12 publications

References 20 publications

Normalized Resistance Interpretation as a Tool for Establishing Epidemiological MIC Susceptibility Breakpoints

Normalized Resistance Interpretation as a Tool for Establishing Epidemiological MIC Susceptibility Breakpoints

Setting interpretive breakpoints for antimicrobial susceptibility testing using disk diffusion

Extended antimicrobial resistance screening of the dominant faecal Escherichia coli and of rare resistant clones

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