Retraction for Flynt et al., “Comparison of Etest to Broth Microdilution for Testing of Susceptibility of Pseudomonas aeruginosa to Ceftolozane-Tazobactam”

Flynt, Lauren K.; Veve, Michael P; Samuel, Linoj; Tibbetts, Robert J.

doi:10.1128/jcm.00541-18

J Clin Microbiol

2018

DOI: 10.1128/jcm.00541-18

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Retraction for Flynt et al., “Comparison of Etest to Broth Microdilution for Testing of Susceptibility of Pseudomonas aeruginosa to Ceftolozane-Tazobactam”

Lauren K. Flynt

Michael P Veve

Linoj Samuel

et al.

Abstract: We hereby retract this article. In our paper we described discrepant results between ceftolozane-tazobactam Etests and broth microdilution. However, when repeat testing on the same isolates was done for a second, larger study recently published by R. M.

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“…Another example is a retracted paper on the performance of the ceftolozane-tazobactam Etest. In this case, the authors compared the Etest to reference broth microdilution, which was performed using drug obtained from the pharmacy and serially diluted, leading to an inappropriate concentration of tazobactam in the test and false resistance by the reference method (7,8). Again, QC testing was within acceptable limits.…”

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Verification Is an Integral Part of Antimicrobial Susceptibility Test Quality Assurance

Humphries

Simner

2020

J Clin Microbiol

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W ith interest we read the commentary of Kirby and colleagues, which advocated implementing antimicrobial susceptibility testing (AST) for new drugs without verification (1). We agree with the authors that new drugs should not be used clinically without an accompanying AST. Implementing AST for new drugs as soon as possible is a critical function of the clinical laboratory. However, we disagree that verification studies beyond quality control (QC) testing are superfluous. We posit that some form of verification is warranted when these tests are implemented to ensure that the laboratory is in compliance with national regulations, i.e., the Clinical and Laboratory Improvement Amendments (CLIA), which require verification of new test systems prior to their use for patients; far more importantly, the laboratory must have confidence that accurate results are obtained with the device. The CLIA view the addition of additional analytes to a test system (e.g., for AST or new drugs) as a unique test system that requires verification (2). Many laboratories are paralyzed by the prospect of performing a verification study for AST, for the reasons outlined by Kirby: time and financial resources are restricted, organisms can be difficult to obtain, and guidance is lacking. Nonetheless, the answer to these hurdles is not to bypass the verification process as a whole. Rather, a risk-based approach to inform the extent of verification activities should be done, taking the organisms to be tested, the laboratory's experience in performing the test for other drugs, and the availability of published information on the new drug AST into consideration. While the CLSI suggests the use of 30 isolates, this is a guideline, and the extent of testing is at the director's discretion. Testing isolates that harbor resistance profiles targeted by the new drug and MICs near the clinical breakpoint may be helpful. An ongoing quality assurance program implemented alongside AST adds additional confidence, ensuring routine investigation of unexpected resistance or susceptibility. Several factors other than those identified by Kirby et al. might impact an AST's performance, new disks, and gradient strip performance: (i) the use of Mueller-Hinton agar of a brand different from that used in the studies conducted by the manufacturer for U.S. Food and Drug Administration (FDA) clearance, (ii) nuanced alteration of the AST method defined in the package insert (e.g., an extension of the incubation period for isolates with poor growth), (iii) testing organisms in a manner other than within the drug's indications for use and for which the AST was not evaluated by the manufacturer (e.g., testing a member of the Enterobacterales that is not claimed in the drug label), (iv) application of clinical breakpoints to interpret the results that are different from those applied at the time of FDA clearance for the device (e.g., the use of CLSI breakpoints), (v) the prevalence of an antimicrobial resistance mechanism not well represented in the AST clearance studies, an...

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confidence: 99%

Verification Is an Integral Part of Antimicrobial Susceptibility Test Quality Assurance

Humphries

Simner

2020

J Clin Microbiol

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Retraction for Flynt et al., “Comparison of Etest to Broth Microdilution for Testing of Susceptibility of Pseudomonas aeruginosa to Ceftolozane-Tazobactam”

Abstract: We hereby retract this article. In our paper we described discrepant results between ceftolozane-tazobactam Etests and broth microdilution. However, when repeat testing on the same isolates was done for a second, larger study recently published by R. M.

Cited by 1 publication

References 0 publications

Verification Is an Integral Part of Antimicrobial Susceptibility Test Quality Assurance

Verification Is an Integral Part of Antimicrobial Susceptibility Test Quality Assurance

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