Performance of three chromogenic VRE screening agars, two Etest® vancomycin protocols, and different microdilution methods in detecting vanB genotype Enterococcus faecium with varying vancomycin MICs

Klare, Ingo; Fleige, Carola; Geringer, Uta; Witte, Wolfgang; Werner, Guido

doi:10.1016/j.diagmicrobio.2012.06.020

Cited by 26 publications

(19 citation statements)

References 39 publications

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“…In a recent study by Klare et al, the VME rates of the chromogenic VRE screening media were higher than those observed in our study (36). The higher VME rates observed by Klare and coworkers could be due to their selection of strains; 43/129 (33%) of their VanB-type E. faecium strains showed MICs of Յ4 mg/liter, thus pushing the detection limits more than our collection, in which only 1 of 27 VRE isolates showed a MIC of 4 mg/liter (Table 1).…”

Section: Discussioncontrasting

confidence: 56%

Performance of the EUCAST Disk Diffusion Method, the CLSI Agar Screen Method, and the Vitek 2 Automated Antimicrobial Susceptibility Testing System for Detection of Clinical Isolates of Enterococci with Low- and Medium-Level VanB-Type Vancomycin Resistance: a Multicenter Study

et al. 2014

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f Different antimicrobial susceptibility testing methods to detect low-level vancomycin resistance in enterococci were evaluated in a Scandinavian multicenter study (n ‫؍‬ 28). A phenotypically and genotypically well-characterized diverse collection of Enterococcus faecalis (n ‫؍‬ 12) and Enterococcus faecium (n ‫؍‬ 18) strains with and without nonsusceptibility to vancomycin was examined blindly in Danish (n ‫؍‬ 5), Norwegian (n ‫؍‬ 13), and Swedish (n ‫؍‬ 10) laboratories using the EUCAST disk diffusion method (n ‫؍‬ 28) and the CLSI agar screen (n ‫؍‬ 18) or the Vitek 2 system (bioMérieux) (n ‫؍‬ 5). The EUCAST disk diffusion method (very major error [VME] rate, 7.0%; sensitivity, 0.93; major error [ME] rate, 2.4%; specificity, 0.98) and CLSI agar screen (VME rate, 6.6%; sensitivity, 0.93; ME rate, 5.6%; specificity, 0.94) performed significantly better (P ‫؍‬ 0.02) than the Vitek 2 system (VME rate, 13%; sensitivity, 0.87; ME rate, 0%; specificity, 1). The performance of the EUCAST disk diffusion method was challenged by differences in vancomycin inhibition zone sizes as well as the experience of the personnel in interpreting fuzzy zone edges as an indication of vancomycin resistance. Laboratories using Oxoid agar (P < 0.0001) or Merck Mueller-Hinton (MH) agar (P ‫؍‬ 0.027) for the disk diffusion assay performed significantly better than did laboratories using BBL MH II medium. Laboratories using Difco brain heart infusion (BHI) agar for the CLSI agar screen performed significantly better (P ‫؍‬ 0.017) than did those using Oxoid BHI agar. In conclusion, both the EUCAST disk diffusion and CLSI agar screening methods performed acceptably (sensitivity, 0.93; specificity, 0.94 to 0.98) in the detection of VanB-type vancomycin-resistant enterococci with low-level resistance. Importantly, use of the CLSI agar screen requires careful monitoring of the vancomycin concentration in the plates. Moreover, disk diffusion methodology requires that personnel be trained in interpreting zone edges.

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Section: Discussioncontrasting

confidence: 56%

Performance of the EUCAST Disk Diffusion Method, the CLSI Agar Screen Method, and the Vitek 2 Automated Antimicrobial Susceptibility Testing System for Detection of Clinical Isolates of Enterococci with Low- and Medium-Level VanB-Type Vancomycin Resistance: a Multicenter Study

et al. 2014

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“…Low sensitivity for recovery of vanB VRE with low vancomycin MICs from commercial chromogenic agars has been demonstrated previously (3,25). In both of these studies, the sensitivity ranged from 94 to 98%; however, these studies are not necessarily comparable to our study for several reasons.…”

Section: Discussioncontrasting

confidence: 53%

“…Test performance depends upon a number of variables that may relate to the patient, the specimen, the assay, or the isolate. Previous studies have suggested that the vancomycin MIC of VRE is a determinant of test sensitivity and that the optimal screening method is hence likely to be dependent upon local VRE epidemiology (3,4). Historically, Australian VRE epidemiology has differed from that in either North America or Europe (5-9), as it is dominated by vanB Enterococcus faecium, of which certain clones have low vancomycin MICs, creating unique challenges for detection during active surveillance (4,10,11 (3,14,15).…”

mentioning

confidence: 99%

“…Previous studies have suggested that the vancomycin MIC of VRE is a determinant of test sensitivity and that the optimal screening method is hence likely to be dependent upon local VRE epidemiology (3,4). Historically, Australian VRE epidemiology has differed from that in either North America or Europe (5-9), as it is dominated by vanB Enterococcus faecium, of which certain clones have low vancomycin MICs, creating unique challenges for detection during active surveillance (4,10,11 (3,14,15). vanB VRE are now more prevalent than vanA VRE in several European centers, including Sweden (16), Spain (17), and Germany (18), while recent Canadian national surveillance demonstrates that vanB strains constitute 10% of all their VRE (19).…”

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confidence: 99%

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Low Vancomycin MICs and Fecal Densities Reduce the Sensitivity of Screening Methods for Vancomycin Resistance in Enterococci

et al. 2014

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cActive surveillance is part of a multifaceted approach used to prevent the spread of vancomycin-resistant enterococci (VRE). The impact of fecal density, the vancomycin MIC of the isolate, and the vancomycin concentration in liquid medium on test performance are uncertain. Using fecal specimens spiked with a collection of 18 VRE (predominantly vanB) with a wide vancomycin MIC range, we compared the performances of commercial chromogenic agars (CHROMagar VRE, chromID VRE, Brilliance VRE, and VRE Select) and 1 liquid medium (Enterococcosel enrichment broth) for VRE detection. The specificity of solid media was excellent; however, the sensitivity at 48 h varied from 78 to 94%. Screening using liquid medium was less sensitive than screening with solid media, particularly as the vancomycin content increased. Sensitivity declined (i) as the fecal VRE density decreased, (ii) when the media were assessed at 24 h (versus 48 h), and (iii) for isolates with a low vancomycin MIC (sensitivity, 25 to 75% versus 100% for isolates with vancomycin MIC of <16 mg/liter versus >32 mg/liter on solid medium using 10 6 CFU/ml of feces). Depending on local epidemiology and in particular VRE vancomycin MICs, the sensitivity of culture-based methods for VRE screening of stool or rectal specimens may be suboptimal, potentially facilitating secondary transmission. Active surveillance is part of a multifaceted infection control approach used to prevent the spread of vancomycin-resistant enterococci (VRE) (1, 2). The ability to detect VRE-colonized patients allows prompt implementation of infection control measures to interrupt the transmission cycle, whereas exclusion of VRE colonization reduces the impact of such activity on patient care and hospital workflow.A variety of in-house and commercial chromogenic solid and liquid media are available for VRE screening in stool or rectal swab specimens. Test performance depends upon a number of variables that may relate to the patient, the specimen, the assay, or the isolate. Previous studies have suggested that the vancomycin MIC of VRE is a determinant of test sensitivity and that the optimal screening method is hence likely to be dependent upon local VRE epidemiology (3, 4). Historically, Australian VRE epidemiology has differed from that in either North America or Europe (5-9), as it is dominated by vanB Enterococcus faecium, of which certain clones have low vancomycin MICs, creating unique challenges for detection during active surveillance (4,10,11 MATERIALS AND METHODSA VRE was defined as an enterococcal isolate that possessed either the vanA or vanB gene regardless of the vancomycin MIC and its relationship to susceptibility breakpoints. This definition has practical validity, as from an infection control perspective, the ability for the resistance mechanism to disseminate is dependent upon the presence of the gene, not the resistance phenotype. Additionally, the vanA and vanB genes are inducible, and hence, MIC expression may be variable (4).Eighteen well-characterized enterococcal stra...

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“…Furthermore, the method allows for the detection of heterogeneous resistant isolates, which is impossible with automated methods [8,9].…”

Section: Introductionmentioning

confidence: 99%

Direct disk diffusion test using European Clinical Antimicrobial Susceptibility Testing breakpoints provides reliable results compared with the standard method

Stokkou

Geginat²,

Schlüter³

et al. 2015

European Journal of Microbiology and Immunology

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Sepsis represents a life-threatening infection requiring the immediate start of antibacterial treatment to reduce morbidity. Thus, laboratories use direct antimicrobial susceptibility testing (AST) to rapidly generate preliminary results from positive blood cultures. As the direct AST has not yet been published to be evaluated with EUCAST breakpoints, the purpose of the study was to investigate the reliability of the direct agar diffusion test to correctly produce AST results from positive monobacterial blood cultures compared with the VITEK2-based definitive AST, when current EUCAST breakpoints were used.A total of 428 isolates from unselected monobacterial routine blood cultures and 110 challenge strains were included. Direct agar diffusion-based and standard VITEK2-based AST of 2803 bacterium-drug combinations yielded a total clinical category agreement of 95.47% with 1.28% very major errors and 3.42% combined major and minor errors. On the species level, very major errors were observed in the species-drug combinations Enterococcus spp.-high-level gentamicin (10.87%) and Staphylococcus spp.-rifampicin (5%), only. No very major errors occurred with Enterobacteriaceae and Pseudomonas aeruginosa.In most species-drug combinations, the direct agar diffusion test using EUCAST breakpoints precisely predicted the result of the definitive antibiotic susceptibility test and, thus, it can be used to optimize empiric antibiotic therapy until definitive results are available.

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Performance of three chromogenic VRE screening agars, two Etest® vancomycin protocols, and different microdilution methods in detecting vanB genotype Enterococcus faecium with varying vancomycin MICs

Cited by 26 publications

References 39 publications

Performance of the EUCAST Disk Diffusion Method, the CLSI Agar Screen Method, and the Vitek 2 Automated Antimicrobial Susceptibility Testing System for Detection of Clinical Isolates of Enterococci with Low- and Medium-Level VanB-Type Vancomycin Resistance: a Multicenter Study

Performance of the EUCAST Disk Diffusion Method, the CLSI Agar Screen Method, and the Vitek 2 Automated Antimicrobial Susceptibility Testing System for Detection of Clinical Isolates of Enterococci with Low- and Medium-Level VanB-Type Vancomycin Resistance: a Multicenter Study

Low Vancomycin MICs and Fecal Densities Reduce the Sensitivity of Screening Methods for Vancomycin Resistance in Enterococci

Direct disk diffusion test using European Clinical Antimicrobial Susceptibility Testing breakpoints provides reliable results compared with the standard method

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