P1645 Comparative evaluation of the VITEK 2, disk diffusion, E-test, and agar dilution susceptibility testing methods for colistin in clinical isolates (including heteroresistant E. cloacae and A. baumannii strains)

2007 ◽  
Vol 29 ◽  
pp. S464
Author(s):  
J. Lo-Ten-Foe ◽  
A. de Smet ◽  
B. Diederen ◽  
J. Kluytmans ◽  
P. van Keulen
Keyword(s):  
Comparative Evaluation ◽  
Susceptibility Testing ◽  
Clinical Isolates ◽  
Disk Diffusion ◽  
Testing Methods ◽  
Agar Dilution ◽  
Vitek 2

scholarly journals Comparative Evaluation of the VITEK 2, Disk Diffusion, Etest, Broth Microdilution, and Agar Dilution Susceptibility Testing Methods for Colistin in Clinical Isolates, Including Heteroresistant Enterobacter cloacae and Acinetobacter baumannii Strains

2007 ◽  
Vol 51 (10) ◽  
pp. 3726-3730 ◽  
Author(s):  
Jerome R. Lo-Ten-Foe ◽  
Anne Marie G. A. de Smet ◽  
Bram M. W. Diederen ◽  
Jan A. J. W. Kluytmans ◽  
Peter H. J. van Keulen
Keyword(s):  
Acinetobacter Baumannii ◽  
Susceptibility Testing ◽  
Enterobacter Cloacae ◽  
Clinical Isolates ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Diffusion Test ◽  
Disk Diffusion Test ◽  
Agar Dilution ◽  
Vitek 2

ABSTRACT Increasing antibiotic resistance in gram-negative bacteria has recently renewed interest in colistin as a therapeutic option. The increasing use of colistin necessitates the availability of rapid and reliable methods for colistin susceptibility testing. We compared seven methods of colistin susceptibility testing (disk diffusion, agar dilution on Mueller-Hinton [MH] and Isosensitest agar, Etest on MH and Isosensitest agar, broth microdilution, and VITEK 2) on 102 clinical isolates collected from patient materials during a selective digestive decontamination or selective oral decontamination trial in an intensive-care unit. Disk diffusion is an unreliable method to measure susceptibility to colistin. High error rates and low levels of reproducibility were observed in the disk diffusion test. The colistin Etest, agar dilution, and the VITEK 2 showed a high level of agreement with the broth microdilution reference method. Heteroresistance for colistin was observed in six Enterobacter cloacae isolates and in one Acinetobacter baumannii isolate. This is the first report of heteroresistance to colistin in E. cloacae isolates. Resistance to colistin in these isolates seemed to be induced upon exposure to colistin rather than being caused by stable mutations. Heteroresistant isolates could be detected in the broth microdilution, agar dilution, Etest, or disk diffusion test. The VITEK 2 displayed low sensitivity in the detection of heteroresistant subpopulations of E. cloacae. The VITEK 2 colistin susceptibility test can therefore be considered to be a reliable tool to determine susceptibility to colistin in isolates of genera that are known not to exhibit resistant subpopulations. In isolates of genera known to (occasionally) exhibit heteroresistance, an alternative susceptibility testing method capable of detecting heteroresistance should be used.

scholarly journals Susceptibility of Clinical Isolates of Escherichia coli to Fosfomycin as Measured by Four In Vitro Testing Methods

2020 ◽  
Vol 58 (10) ◽  
Author(s):  
James A. Karlowsky ◽  
Philippe R. S. Lagacé-Wiens ◽  
Nancy M. Laing ◽  
Melanie R. Baxter ◽  
Heather J. Adam ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Reference Method ◽  
Clinical Isolates ◽  
Disk Diffusion ◽  
Content Type ◽  
E Coli ◽  
Agar Dilution ◽  
Vitek 2 ◽  
Urinary Isolates

ABSTRACT Clinical isolates of Escherichia coli (n = 554) were tested against fosfomycin using agar dilution, disk diffusion, and Etest. Agar dilution (reference method) identified few isolates with fosfomycin MICs of 64 (n = 3), 128 (n = 4), and ≥256 μg/ml (n = 2). Applying CLSI (M100, 2020) and EUCAST (v. 10.0, 2020) breakpoints, 98.9% and 98.4% (agar dilution), 99.3% and 99.1% (disk diffusion), and 99.1% and 98.9% (Etest) of isolates were fosfomycin susceptible, respectively. Essential agreement (agar dilution versus Etest) was low (40.8%); 59.3% (131/221) of isolates with agar dilution MICs of 2 to 128 μg/ml tested 2 to 4 doubling dilutions lower by Etest. Applying CLSI breakpoints, categorical agreement was >99% for both disk diffusion and Etest; no major errors (MEs) or very major errors (VMEs) were identified, and rates of minor errors (mEs) were <1%. EUCAST breakpoints yielded categorical agreements of >99% and no MEs for both disk diffusion and Etest; however, VMEs occurred at unacceptable rates of 44.4% (disk diffusion) and 33.3% (Etest). All isolates with agar dilution MICs of ≥32 μg/ml (n = 12) and a subset of isolates with MICs of ≤16 μg/ml (n = 49) were also tested using the Vitek 2 AST-N391 card and generated fosfomycin MICs 1 to ≥3 doubling dilutions lower than agar dilution for 11/12 isolates with agar dilution MICs of ≥32 μg/ml. We conclude that performing fosfomycin disk diffusion or Etest on urinary isolates of E. coli and interpreting results using CLSI breakpoints reliably identified fosfomycin-susceptible isolates regardless of differences in endpoint reading criteria. EUCAST breakpoints generated excessive rates of VMEs for our isolate collection of high fosfomycin susceptibility.

scholarly journals 710. In Vitro Activity and Performance of Available Susceptibility Testing Methods for Eravacycline Against Carbapenem-Resistant Enterobacteriaceae (CRE)

2019 ◽  
Vol 6 (Supplement_2) ◽  
pp. S319-S320
Author(s):  
Chelsea E Jones ◽  
Ellen G Kline ◽  
Minh-Hong Nguyen ◽  
Cornelius J Clancy ◽  
Ryan K Shields
Keyword(s):  
Susceptibility Testing ◽  
Multidrug Resistant ◽  
Vitro Activity ◽  
Clinical Isolates ◽  
Disk Diffusion ◽  
In Vitro Activity ◽  
Testing Methods ◽  
And Performance ◽  
Susceptibility Breakpoint

Abstract Background Eravacycline (ERV) is a recently-approved, fully synthetic fluorocycline agent that demonstrates broad in vitro activity against multidrug-resistant pathogens. We sought to compare the activity of ERV with minocycline (MIN) and tigecycline (TGC) against diverse CRE clinical isolates, and to evaluate the performance of commercially-available susceptibility testing methods. Methods ERV, MIN, and TGC minimum inhibitory concentrations (MICs) were determined in triplicate by broth microdilution against previously characterized CRE isolates. ERV susceptibility was also measured by disk diffusion (20 µg disk; Mast Group) and MIC test strips (MTS; Liofilchem) according to manufacturer instructions. Results 148 CRE were tested, including 92 K. pneumoniae, 32 Enterobacter spp, 11 E. coli, 5 C. freundii, 4 K. oxytoca, and 4 S. marcescens. 72% of isolates harbored blaKPC, which encoded KPC-2 (n = 33), KPC-3 (n = 48), and other KPC variants (n = 22). 77% and 19% of isolates were resistant to meropenem and ceftazidime–avibactam, respectively. By BMD, the ERV, MIN, and TGC MIC range, MIC50 and MIC90 for shown in the Table. ERV MICs were ≥2-fold lower than MIN and TGC against 99% and 43% of isolates, respectively. ERV MICs did not vary by species or KPC-subtype. ERV MICs determined by BMD and MTS were well-correlated showing 89% essential agreement (MIC within one 2-fold dilution; Figure). The rate of categorical agreement (CA) was 73%. By comparison, the CA rate between BMD and disk diffusion was 78%. By both MTS and disk diffusion methods, susceptibility results clustered on either side of the susceptibility breakpoint. 50% of disk diffusion zones clustered between 14 and 16 millimeters (mm), which is 1 mm on either side of the susceptibility breakpoint (≥15 mm). Conclusion This study confirms the in vitro activity of ERV against CRE clinical isolates, which is comparable to TGC. ERV MTS demonstrated high rates of EA, but lower rates of CA. Clinicians should be aware of the nuances of ERV susceptibility testing and recognize that the modal distribution of ERV MICs against CRE lies on either side of the susceptibility breakpoint. Disclosures All authors: No reported disclosures.

scholarly journals Comparative evaluation of broth microdilution with E-test, Vitek 2, and disk diffusion for susceptibility testing of colistin on Gram-negative bacteria

2021 ◽  
Vol 73 ◽  
pp. 93-98
Author(s):  
Parul Gupta ◽  
Rajni Sharma ◽  
Aruna Vyas ◽  
Amit Tak
Keyword(s):  
Gold Standard ◽  
Susceptibility Testing ◽  
Multidrug Resistant ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Testing Methods ◽  
Geometric Means ◽  
Gram Negative ◽  
Vitek 2 ◽  
Good Concordance

Objectives: With the increasing threat of multidrug-resistant organisms, colistin has become popular in clinical practice. A better understanding of antimicrobial susceptibility testing methods for colistin is needed for optimal patient management. The aim of the study was to determine the accuracy of E-test, Vitek 2 system for the detection of colistin minimum inhibitory concentrations (MIC) against broth microdilution (BMD). Material and Methods: A total of 100 isolates of Gram-negative bacilli were subjected to susceptibility testing for colistin using the following methods: BMD, E-test, Vitek 2, and disk diffusion. Using BMD as the gold standard, comparative analysis between different methods was carried out. Results: Comparison of MIC values of E-test (GM = 0.488 mg/ml) against BMD (GM = 0.611 mg/ml using unpaired t-test (t = 2.015, P = 0.045) showed that geometric means of MIC values of E-strip were significantly lower than BMD. Similarly, comparison of MIC values of Vitek 2 system (GM = 0.615 mg/ml) against BMD (GM = 0.611 mg/ml) using unpaired t-test (t = −0.050, P = 0.960) showed no statistical significant differences in geometric means of MIC values. Taking reference as BMD method – the EA for E-strip is 57%, CA is 97%, VME is 2%, and no ME. Similarly, for the Vitek method EA is 64%, CA is 98%, VME is 1%, and ME is 1%. Conclusion: Different susceptibility testing methods for colistin show great variation in their results and BMD is the best candidate as gold standard. The Vitek 2 method showed good concordance with BMD.

scholarly journals Comparison of Agar Dilution, Disk Diffusion, MicroScan, and Vitek Antimicrobial Susceptibility Testing Methods to Broth Microdilution for Detection of Fluoroquinolone-Resistant Isolates of the FamilyEnterobacteriaceae

1999 ◽  
Vol 37 (3) ◽  
pp. 544-547 ◽  
Author(s):  
Christine D. Steward ◽  
Sheila A. Stocker ◽  
Jana M. Swenson ◽  
Caroline M. O’Hara ◽  
Jonathan R. Edwards ◽  
...  
Keyword(s):  
Antimicrobial Susceptibility ◽  
Susceptibility Testing ◽  
Error Rates ◽  
Disk Diffusion ◽  
Fluoroquinolone Resistance ◽  
Broth Microdilution ◽  
Major Error ◽  
Testing Methods ◽  
Minor Error ◽  
Agar Dilution

Fluoroquinolone resistance appears to be increasing in many species of bacteria, particularly in those causing nosocomial infections. However, the accuracy of some antimicrobial susceptibility testing methods for detecting fluoroquinolone resistance remains uncertain. Therefore, we compared the accuracy of the results of agar dilution, disk diffusion, MicroScan Walk Away Neg Combo 15 conventional panels, and Vitek GNS-F7 cards to the accuracy of the results of the broth microdilution reference method for detection of ciprofloxacin and ofloxacin resistance in 195 clinical isolates of the familyEnterobacteriaceae collected from six U.S. hospitals for a national surveillance project (Project ICARE [Intensive Care Antimicrobial Resistance Epidemiology]). For ciprofloxacin, very major error rates were 0% (disk diffusion and MicroScan), 0.9% (agar dilution), and 2.7% (Vitek), while major error rates ranged from 0% (agar dilution) to 3.7% (MicroScan and Vitek). Minor error rates ranged from 12.3% (agar dilution) to 20.5% (MicroScan). For ofloxacin, no very major errors were observed, and major errors were noted only with MicroScan (3.7% major error rate). Minor error rates ranged from 8.2% (agar dilution) to 18.5% (Vitek). Minor errors for all methods were substantially reduced when results with MICs within ±1 dilution of the broth microdilution reference MIC were excluded from analysis. However, the high number of minor errors by all test systems remains a concern.

scholarly journals Subpopulations of Helicobacter pyloriAre Responsible for Discrepancies in the Outcome of Nitroimidazole Susceptibility Testing

1999 ◽  
Vol 43 (6) ◽  
pp. 1484-1486 ◽  
Author(s):  
E. J. van der Wouden ◽  
A. de Jong ◽  
J. C. Thijs ◽  
J. H. Kleibeuker ◽  
A. A. van Zwet
Keyword(s):  
Helicobacter Pylori ◽  
Susceptibility Testing ◽  
Clinical Isolates ◽  
Disk Diffusion ◽  
Agar Dilution ◽  
H Pylori

ABSTRACT Metronidazole susceptibility testing by E test was compared to that by disk diffusion for 263 Helicobacter pylori isolates and to that by breakpoint agar dilution for 90 H. pyloriisolates. In 5% and 6% of the cases, respectively, results were discrepant. For each of 52 clinical isolates an E test was performed on 10 separate colonies. Subpopulations of resistant and susceptible bacteria were found in five cases. From three isolates, each colony was subcultured and tested up to 10 times. All but 1 of 292 tests showed the same result. We conclude that the E test is reliable and that subpopulations are responsible for discordant results.

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