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VITEK® 2 AST-Gram Positive Lefamulin is designed for antimicrobial susceptibility testing of Gram positive microorganisms 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 AST-Gram Positive Lefamulin is a quantitative test. Lefamulin has been shown to be active against most strains of the microorganisms listed below, according to the FDA label for this antimicrobial.

Active both in vitro and in clinical infections: Staphylococcus aureus (methicillin-susceptible isolates)

The VITEK® 2 Gram-positive Susceptibility Card is intended for use with the VITEK® 2 Systems in clinical laboratories as an in vitro test to determine the susceptibility of Staphylococcus spp., and S. agalactive 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 (0).

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-GP Lefamulin (≤ 0.03 –>4 µg/mL) has the following concentrations in the card: 0.125, 0.5, 1, and 2 (equivalent standard method concentration by efficacy in ug/mL).

The VITEK® 2 AST-Gram Positive Lefamulin (≤ 0.03 - ≥4 µg/mL) device is an antimicrobial susceptibility testing system designed for Gram-positive microorganisms. The acceptance criteria and performance of the device are detailed below.

1. Table of Acceptance Criteria and Reported Device Performance

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

The test set included:

• 404 isolates for Essential Agreement reporting and 404 isolates for Category Agreement reporting (derived from the numerators/denominators in Table 2).
• 3 resistant isolates were tested for VME (Very Major Error)
• 401 susceptible isolates were tested for ME (Major Error)

The data provenance is described as an "external evaluation" conducted with "fresh and stock clinical isolates, as well as a set of challenge strains." The document does not specify the country of origin of the data or explicitly state whether the study was retrospective or prospective.

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 given text.

4. Adjudication method for the test set

This information is not provided in the given text.

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

A multi-reader multi-case (MRMC) comparative effectiveness study with human readers assisted by AI is not applicable to this device. This device is an automated antimicrobial susceptibility test system, not an AI-assisted diagnostic tool interpreted by human readers.

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

Yes, a standalone performance evaluation was done. The VITEK® 2 AST-GP Lefamulin system's performance was compared directly to the CLSI broth microdilution reference method (the ground truth), without human intervention in the interpretation of the VITEK® 2 results. The system automatically generates MIC values and interpretive categories.

7. The type of ground truth used

The ground truth used was the CLSI broth microdilution reference method, incubated at 16-20 hours.

8. The sample size for the training set

The document does not explicitly mention a separate "training set" or its sample size. The description focuses on the external evaluation data used for performance assessment. As an AST system, the device's "training" for MIC determination is inherent in its design based on established microdilution principles and may not involve a distinct, large-scale machine learning training set in the way an AI algorithm might.

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

Since a distinct training set is not explicitly mentioned as per the prompt's context (e.g., for an AI algorithm), details on how its ground truth was established are not provided. The device's operation is based on established microbiological principles, and its performance is validated against the CLSI broth microdilution reference method.

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