Verification and validation of procedures in the clinical microbiology laboratory

Elder, B. Laurel

doi:10.1016/s0196-4399(97)83919-0

Cited by 54 publications

(48 citation statements)

References 4 publications

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“…Standard antimicrobial susceptibility testing definitions were used (7,18). For MICs measured with a continuous concentration scale (i.e., Etest) that yielded results falling in between conventional serial twofold dilutions, the next higher dilution was assigned.…”

Section: Methodsmentioning

confidence: 99%

Comparative Evaluation of Etest and Sensititre YeastOne Panels against the Clinical and Laboratory Standards Institute M27-A2 Reference Broth Microdilution Method for Testing Candida Susceptibility to Seven Antifungal Agents

Byrne²,

et al. 2007

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To assess their utility for antifungal susceptibility testing in our clinical laboratory, the Etest and Sensititre methods were compared with the Clinical and Laboratory Standards Institute (CLSI) M27-A2 reference broth microdilution method. Fluconazole (FL), itraconazole (I), voriconazole (V), posaconazole (P), flucytosine (FC), caspofungin (C), and amphotericin B (A) were tested with 212 Candida isolates. Reference MICs were determined after 48 h of incubation, and Etest and Sensititre MICs were determined after 24 h and 48 h of incubation. Overall, excellent essential agreement (EA) between the reference and test methods was observed for Etest (95%) and Sensititre (91%). Etest showed an >92% EA for MICs for all drugs tested; Sensititre showed a >92% EA for MICs for I, FC, A, and C but 82% for FL and 85% for V. The overall categorical agreement (CA) was 90% for Etest and 88% for Sensititre; minor errors accounted for the majority of all categorical errors for both systems. Categorical agreement was lowest for Candida glabrata and Candida tropicalis with both test systems. Etest and Sensititre provided better CA at 24 h compared to 48 h for C. glabrata; however, CA for C. glabrata was <80% for FL with both test systems despite MIC determination at 24 h. Agreement between technologists for both methods was >98% for each agent against all organisms tested. Overall, Etest and Sensititre methods compared favorably with the CLSI reference method for determining the susceptibility of Candida. However, further evaluation of their performance for determining the MICs of azoles, particularly for C. glabrata, is warranted.

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Section: Methodsmentioning

confidence: 99%

Comparative Evaluation of Etest and Sensititre YeastOne Panels against the Clinical and Laboratory Standards Institute M27-A2 Reference Broth Microdilution Method for Testing Candida Susceptibility to Seven Antifungal Agents

Byrne²,

et al. 2007

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“…Interpretative discrepancies were classified as very major, major, or minor errors. Very major errors occurred when the results obtained by the participant were in the susceptible category, whereas they were in the resistant category with the reference method; the number of susceptibility testing determinations with the reference resistant interpretation result was used as the denominator (8). Conversely, major errors occurred when the results obtained by the participant were in the resistant category, whereas they were in the susceptible category with the reference method; the number of susceptibility testing determinations with the reference susceptible interpretation result was used as the denominator (8) …”

Section: Methodsmentioning

confidence: 99%

Quality Control for β-Lactam Susceptibility Testing with a Well-Defined Collection of Enterobacteriaceae and Pseudomonas aeruginosa Strains in Spain

et al. 2003

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Eighteen Enterobacteriaceae and Pseudomonas aeruginosa strains, 16 of them with well-defined ␤-lactam re sistance mechanisms, were sent to 52 Spanish microbiology laboratories. Interpretative categories for 8 extended-spectrum ␤-lactams were collected. Participating laboratories used their own routine susceptibility testing procedures (88% automatic systems, 10% disk diffusion, and 2% agar dilution). Control results were established by two independent reference laboratories by applying the NCCLS microdilution method and interpretative criteria. Interpretative discrepancies were observed in 16% of the results (4.4% for cefepime, 3.0% for aztreonam, 2.8% for piperacillin-tazobactam, 1.7% for cefotaxime [CTX] and ceftazidime, 1.1% for ceftriaxone, 0.9% for meropenem, and 0.3% for imipenem). High consistency with reference values (<5% of major plus very major errors) was observed with (i) American Type Culture Collection quality control strains; (ii) strains with low-efficiency mechanisms inactivating extended-spectrum ␤-lactams, such as OXA-1-producing Escherichiacoli or SHV-1-hyperproducing Klebsiella pneumoniae; (iii) strains with highly efficient mechanisms, such as SHV-5 porin-deficient K. pneumoniae, CTX-M-10 in Enterobacter cloacae hyperproducing AmpC, and P. aeruginosa with the MexAB OprM efflux phenotype or hyperproducing AmpC. Low consistency (>30% major plus very major errors) was detected in K1-producing Klebsiella oxytoca, CTX-M-9-producing E. coli, and in OprD ؊ P. aeruginosa strains. Extended-spectrum ␤-lactamase (ESBL)-producing strains accounted for 86% of very major errors. Recognition of the ESBL phenotype was particularly low in Enterobacter cloacae strains (<35%), due to the lack of NCCLS-specific rules in this genus. A K1-producing K. oxytoca was misidentified by 10% of laboratories as an ESBL producer. The use of well-defined resistant strains is useful for improving proficiency in susceptibility testing in clinical laboratories.Antimicrobial susceptibility testing is one of the most important tasks of clinical microbiology laboratories (11). It is performed daily in clinical laboratories by standardized methods. The disk diffusion technique has been extensively used for this objective; however, semiautomated or automated systems based on microdilution techniques are replacing this method, at least for nonfastidious organisms (9).Quality assurance of antimicrobial susceptibility testing is commonly performed by using internal quality control protocols, which monitor the precision and accuracy of the method, the performance of the reagents, and the performance of the microbiologist or technicians carrying out these procedures (14). These protocols often use organisms susceptible to the majority of antimicrobial agents (24) and, to a lesser extent, resistant strains (36). Additional external quality control assessments (proficiency testing) are necessary in the quality assurance of antimicrobial susceptibility testing methods (2). In this case, organisms with susceptibility defined by reference ...

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“…Positive and negative controls were used in all tests. Tests were read at 2 and 4 h. Sensitivities, specificities, positive predictive values (PPV), and negative predictive values (NPV) were calculated according to the method of Elder (2). Of 81 positive blood culture bottles from unique patients with initial Gram stains showing gram-positive cocci in clusters, the DTC test demonstrated a sensitivity of 56.7% at 2 h and 93.3% at 4 h while the thermostable DNase test had a sensitivity of 96.7% at 2 h and 100% at 4 h ( Table 1).…”

mentioning

confidence: 99%

Thermostable DNase Is Superior to Tube Coagulase for Direct Detection of Staphylococcus aureus in Positive Blood Cultures

Lagacé-Wiens¹,

Alfa

Manickam

et al. 2007

J Clin Microbiol

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ᰔIn a recent edition of the Journal of Clinical Microbiology, Qian et al. described the sensitivity and specificity of the direct tube coagulase (DTC) test for the presumptive identification of Staphylococcus aureus directly from positive blood culture bottles from which Gram stains were consistent with staphylococci (7). The reported sensitivities of 34% at 2 h of incubation and 65% at 4 h of incubation (7) are considerably lower than those previously described and suggest an unacceptably high rate of false negatives (1,4,5,6,8,9,11). The authors draw the conclusion that despite its low sensitivity the DTC test is clinically valuable, particularly in experienced hands, because of its low cost and simplicity (7).However, Qian et al. neither evaluated nor commented on the use of the thermostable DNase test for the presumptive identification of S. aureus directly from positive blood culture bottles, as described by Madison and Baselski (4) and others (1,6,8,9,10). In these studies, the thermostable DNase test has been reported to be sensitive (85% to 100%) and specific (93 to 100%), to have a high degree of correlation with the DTC test (92.7 to 100%), to be relatively simple to perform, and to have low material cost (1,4,6,8,9,10). In our laboratory, the material cost per test is 79¢, compared to 22 ¢ for the DTC test. Furthermore, the thermostable DNase test has the advantage of having a more rapid turn-around time than the DTC test, often being positive at 1 h (4, 8).We recently compared the thermostable DNase test with the DTC test for the presumptive identification of S. aureus from BacT/Alert (bioMérieux, Marcy l'É toile, France) blood culture bottles in two tertiary-care teaching hospitals over a period of 50 days. The DTC test was performed by mixing 50 l of positive blood culture broth with 450 l of rabbit plasma (Becton Dickinson, Oakville, Ontario, Canada) in a glass test tube and incubating at 37°C. The thermostable DNase test was performed using the agar diffusion method. A 2-ml aliquot of blood culture broth was boiled for 15 min and then cooled to room temperature. Six-millimeter holes were cut in toluidine blue DNase agar plates produced in-house according to the method described by Lachica et al. (3), and 100 l of the boiled blood culture broth was placed into the well and then incubated at 37°C. Positive and negative controls were used in all tests. Tests were read at 2 and 4 h. Sensitivities, specificities, positive predictive values (PPV), and negative predictive values (NPV) were calculated according to the method of Elder (2). Of 81 positive blood culture bottles from unique patients with initial Gram stains showing gram-positive cocci in clusters, the DTC test demonstrated a sensitivity of 56.7% at 2 h and 93.3% at 4 h while the thermostable DNase test had a sensitivity of 96.7% at 2 h and 100% at 4 h ( Table 1). The specificity for both methods was 100% at both 2 and 4 h.Based on our findings, we propose that although the DTC test used with BacT/Alert blood culture bottles has an acceptabl...

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Verification and validation of procedures in the clinical microbiology laboratory

Cited by 54 publications

References 4 publications

Comparative Evaluation of Etest and Sensititre YeastOne Panels against the Clinical and Laboratory Standards Institute M27-A2 Reference Broth Microdilution Method for Testing Candida Susceptibility to Seven Antifungal Agents

Comparative Evaluation of Etest and Sensititre YeastOne Panels against the Clinical and Laboratory Standards Institute M27-A2 Reference Broth Microdilution Method for Testing Candida Susceptibility to Seven Antifungal Agents

Quality Control for β-Lactam Susceptibility Testing with a Well-Defined Collection of Enterobacteriaceae and Pseudomonas aeruginosa Strains in Spain

Thermostable DNase Is Superior to Tube Coagulase for Direct Detection of Staphylococcus aureus in Positive Blood Cultures

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