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VITEK 2 AST-Gram Negative Cefazolin is designed for antimicrobial susceptibility testing of Gram-negative bacilli and is intended for use with the VITEK 2 Systems as a laboratory aid in the determination of in vitro susceptibility to antimicrobial agents.

VITEK 2 AST-Gram Negative Cefazolin (≤1-≥32 µg/mL) is a quantitative test. Testing is indicated for Enterobacterales (from infections other than uncomplicated UTI) as recognized by the FDA Susceptibility Test Interpretive Criteria (STIC).

VITEK 2 AST-Gram Negative Cefazolin (≤1-≥32 µg/mL) has demonstrated acceptable performance with the following organisms:

Enterobacterales (Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Klebsiella oxytoca, Citrobacter koseri)

The VITEK 2 Gram Negative Susceptibility Card is intended for use with the VITEK 2 Systems in clinical laboratories as an in vitro test to determine the susceptibility of clinically significant aerobic Gram- negative bacilli to antimicrobial agents when used as instructed.

The principle of the VITEK® 2 AST cards is based on the microdilution minimum inhibitory concentration (MIC) technique reported by MacLowry and Marsh (1) and Gerlach (2). The VITEK® 2 AST card is essentially a miniaturized, abbreviated and automated version of the doubling dilution technique (3).

Each VITEK® 2 AST card contains 64 wells. A control well which only contains microbiological culture media is resident on all cards. The remaining wells contain premeasured portions of a specific antibiotic combined with culture media. The bacterial or yeast isolate to be tested is diluted to a standardized concentration with 0.45 – 0.5% saline before being used to rehydrate the antimicrobial medium within the card. The VITEK® 2 System automatically fills, seals and places the card into the incubator/reader. The VITEK® 2 Compact has a manual filling, sealing and loading operation. The VITEK® 2 Systems monitor the growth of each well in the card over a defined period of time. At the completion of the incubation cycle, a report is generated that contains the MIC value along with the interpretive category result for each antibiotic contained on the card.

VITEK® 2 AST-GN Cefazolin has the following concentrations in the card: 1, 2, and 8 (equivalent standard method concentration by efficacy in µg/mL).

The provided text describes the acceptance criteria and a study proving the device meets these criteria for the VITEK 2 AST-Gram Negative Cefazolin antimicrobial susceptibility testing system.

Here's a breakdown of the requested information:

1. Table of Acceptance Criteria and Reported Device Performance

Note on Acceptance Criteria: The document references the "FDA Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA (Issued August 28, 2009)" for defining acceptable performance. While specific numerical acceptance criteria (e.g., for EA, CA, VME, ME) are not explicitly listed in the provided text, they are implied by the reported performance metrics and the statement that the device "demonstrated substantially equivalent performance." For AST systems, the FDA typically looks for high Essential and Category Agreement, with very low rates of Major and Very Major Errors. The low Category Agreement (86.8%) is acknowledged and attributed mainly to minor errors.

2. Sample Size Used for the Test Set and Data Provenance

• Sample Size for Test Set:
  • Total isolates tested: 862 (derived from the denominator for EA and CA calculations).
  • The study included "fresh and stock clinical isolates" as well as "a set of challenge strains."
• Data Provenance:
  • The study was an "external evaluation." This typically implies data collected from multiple sites outside of the manufacturer's primary lab.
  • The document does not specify the country of origin for the data.
  • The study included both "fresh" and "stock" clinical isolates, suggesting a mix of prospective (fresh isolates) and retrospective (stock isolates) data collection.

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications

The document does not specify the number or qualifications of experts used to establish the ground truth.

4. Adjudication Method for the Test Set

The document does not describe an adjudication method for the test set. For AST devices, the "ground truth" is typically established by a reference method (broth microdilution in this case), not by expert consensus or adjudication in the way it might be for an imaging AI device.

5. If a Multi Reader Multi Case (MRMC) Comparative Effectiveness Study Was Done, and Effect Size of Improvement

No, a Multi Reader Multi Case (MRMC) comparative effectiveness study was not performed. This type of study (human readers assisting vs. not assisting) is typically relevant for interpretative diagnostic devices, especially in imaging, where human interpretation is a key part of the workflow. The VITEK 2 AST system is an automated device for determining antimicrobial susceptibility, not directly for human interpretation or image reading.

6. If a Standalone (i.e., Algorithm Only Without Human-in-the-Loop Performance) Was Done

Yes, the primary performance study presented is a standalone (algorithm only) performance study. The device's performance (VITEK 2 AST-GN Cefazolin) was compared directly against the CLSI broth microdilution reference method. There is no mention of human-in-the-loop performance evaluation, as the VITEK 2 system is automated.

7. The Type of Ground Truth Used

The type of ground truth used was: Reference Method Comparison.
Specifically, the performance of the VITEK 2 AST-GN Cefazolin was compared to the CLSI broth microdilution reference method, incubated for 16-20 hours. This is the gold standard for antimicrobial susceptibility testing.

8. The Sample Size for the Training Set

The document does not specify the sample size for the training set. This submission is for a 510(k) clearance, which typically focuses on the performance of the final device rather than the specifics of its development (like training data for AI/ML models). The VITEK 2 system relies on growth pattern analysis algorithms rather than deep learning models that require large, labeled training datasets in the conventional sense. Its "training" would likely involve optimizing these algorithms based on extensive internal validation.

9. How the Ground Truth for the Training Set Was Established

The document does not describe how the ground truth for the training set was established, as details on the development of the device's analysis algorithms (likely proprietary) are not typically included in a 510(k) summary. Given the nature of AST systems, any "ground truth" used during development would also likely stem from comparisons to established reference methods like broth microdilution, similar to the test set's ground truth.

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