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VITEK® 2 Gram Negative Ceftolozane Tazobactam is designed for antimicrobial susceptibility testing of Gram negative bacilli and is intended for use with the VITEK® 2 and VITEK® 2 Compact Systems as a laboratory aid in the determination of in vitro susceptibility to antimicrobial agents. VITEK® 2 Gram Negative Ceftolozane/Tazobactam is a quantitative test. Ceftolozane Tazobactam has been shown to be active against most strains of the microorganisms listed below, according to the FDA label for this antimicrobial.

Active in vitro and in clinical infections Enterobacter cloacae Escherichia coli Klebsiella oxytoca Klebsiella pneumoniae Proteus mirabilis Pseudomonas aeruginosa

In vitro data available but clinical significance is unknown Citrobacter freundii Citrobacter koseri Enterobacter aerogenes Enterobacter cloacae Proteus vulgaris Providencia stuartii Serratia liquefacians

The VITEK® 2 Antimicrobial Susceptibility Test (AST) is intended to be used with the VITEK® 2 Systems for the automated quantitative or qualitative susceptibility testing of isolated colonies for the most clinically significant aerobic gram-negative bacilli, Staphylococus spp., Enterococcus spp. and clinically significant yeast

The VITEK® 2 AST Cards are essentially miniaturized versions of the doubling dilution technique for determining the minimum inhibitory concentration (MIC) microdilution methodology.

The isolate to be tested is diluted to a standardized concentration in 0.45 - 0.50% saline before being used to rehydrate the antimicrobial medium within the card. The VITEK® 2 automatically fills, seals and places the card into the incubator/reader. The VITEK® 2 Compact has a manual filling and sealing operation. The VITEK® 2 monitors the growth of each well in the card over a defined period of time (up to 18 hours). At the completion of the incubation cycle, a report is generated that contains the MIC value along with the interpretive category result for each antimicrobial contained on the card.

Here's an analysis of the provided text regarding the acceptance criteria and study for the VITEK® 2 AST-GN Ceftolozane/Tazobactam device.

It's important to note that this document is a 510(k) summary, which provides an overview. More detailed information about the study design, particularly regarding the training set and specific expert qualifications, might be found in the full 510(k) submission, which is not provided here.

Acceptance Criteria and Device Performance

1. Table of Acceptance Criteria and Reported Device Performance

Explanation of Agreement Measures:

• Essential Agreement (EA): Compares the MIC (Minimum Inhibitory Concentration) results from the device to the reference method within one doubling dilution.
• Category Agreement (CA): Compares the interpretive category (Susceptible, Intermediate, Resistant) from the device to the reference method.

Note: The specific numerical acceptance criteria (e.g., "EA > 90%") for AST systems are often detailed in the "FDA Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems," which is referenced in the document but not fully quoted here. However, the reported performance values of 94.8% EA and 98.4% CA are generally considered excellent for AST systems.

Study Details

2. Sample size used for the test set and the data provenance

• Sample Size for Test Set: The document states an "external evaluation was conducted with fresh and stock clinical isolates, as well as a set of challenge strains." It does not provide an exact number of isolates for the test set.
• Data Provenance:
  • Country of Origin: Not specified in the provided text.
  • Retrospective or Prospective: Both "fresh" clinical isolates (suggesting prospective collection or recent isolates) and "stock" clinical isolates (suggesting retrospective/archived) were used. Additionally, "challenge strains" were included, which are typically well-characterized strains used for validation.

3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts

• This information is not provided in the text. Establishing ground truth for AST systems doesn't typically involve multiple human "experts" in the same way an imaging study would. Instead, the ground truth is established by a reference method, performed in a laboratory setting.

4. Adjudication method for the test set

• The concept of "adjudication" in the sense of multiple human readers resolving discrepancies is not applicable here. The test set's ground truth is determined by the CLSI broth microdilution reference method. Discrepancies between the device and the reference method would be analyzed in terms of "major errors," "minor errors," and "very major errors" as defined in AST guidance documents, rather than human adjudication.

5. If a multi-reader multi-case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance

• No, an MRMC comparative effectiveness study was not done. This device (VITEK® 2 AST-GN) is an automated system for determining antimicrobial susceptibility, not an AI-assisted diagnostic tool that human readers would interpret. Its function is to provide a result (MIC and interpretive category) from a sample, not to assist humans in interpreting complex images or clinical data.

6. If a standalone (i.e. algorithm only without human-in-the loop performance) was done

• Yes, this was a standalone performance study. The VITEK® 2 system is an automated instrument that processes samples and provides results without human intervention for interpretation once the test is initiated. The "performance" described (Essential Agreement, Category Agreement) directly refers to the algorithm/system's output compared to the reference method.

7. The type of ground truth used

• The ground truth used was the CLSI broth microdilution reference method, incubated at 16-20 hours. This is the gold standard method for determining antimicrobial susceptibility in microbiology laboratories.

8. The sample size for the training set

• This information is not provided in the text. For a microbiology AST system like VITEK® 2, the "training set" would likely refer to the isolates used during the development and calibration of the instrument's algorithms (e.g., growth curve analysis, MIC determination). The summary focuses on the external evaluation data, which serves as the independent test set.

9. How the ground truth for the training set was established

• This information is not provided in the text. By inference, it would have been established by the same means as the test set: the CLSI broth microdilution reference method.

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