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VITEK® 2 Streptococcus Penicillin is designed for antimicrobial susceptibility testing of Streptococcus species 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 Streptococcus Penicillin is a quantitative test. Penicillin 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: Beta hemolytic Streptococci groups C and G Streptococcus pyogenes Streptococcus agalactiae Streptococcus viridans group Streptococcus pneumoniae

The VITEK® 2 Streptococcus Susceptibility Card is intended for use with the VITEK® 2 Systems in clinical laboratories as an in vitro test to determine the susceptibility of Sireptococcus pneumoniae, beta-hemolytic Streptococcus, and Viridans Streptococcus 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 Streptococcus Penicillin has the following concentrations in the card: 0.06, 0.12, 0.5, and 2ug/mL (equivalent standard method concentration by efficacy in ug/mL).

Here's a summary of the acceptance criteria and study details for the VITEK® 2 Streptococcus Penicillin device:

1. Acceptance Criteria and Reported Device Performance

The device performance is compared to the broth microdilution reference method. The key metrics are Essential Agreement (EA) and Category Agreement (CA), along with Very Major Errors (VME), Major Errors (ME), and Minor Errors (mE).

The document states that the device "demonstrated substantially equivalent performance when compared with the broth microdilution reference method, as defined in the FDA Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA (Issued August 28, 2009)." This guidance document typically outlines specific numerical acceptance criteria for EA, CA, VME, ME, and mE, which are implicitly met by the reported percentages being considered "acceptable."

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

The sample sizes for the test set are embedded within the "Reported Device Performance" column (e.g., 350 for Streptococcus pneumoniae (non-meningitis), 391 for Streptococcus Viridans group, 833 for Beta-hemolytic Streptococcus).

The data provenance is from "external evaluation... conducted with fresh and stock clinical isolates, as well as a set of challenge strains." This implies a combination of retrospective (stock clinical isolates) and prospective (fresh clinical isolates) data. The country of origin of the data is not specified in the provided text.

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

This information is not provided in the document. The ground truth is established by the CLSI broth microdilution reference method, but details on expert involvement in this process (e.g., reading/interpreting the reference method results) are not mentioned.

4. Adjudication Method for the Test Set

This information is not explicitly provided in the document. The study compares the VITEK® 2 results to the CLSI broth microdilution reference method. Adjudication might be part of the standard CLSI method, but it is not detailed here for discrepancies.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done

No, a multi-reader multi-case (MRMC) comparative effectiveness study was not done. This study focuses on the performance of an automated diagnostic device against a reference method, not on human reader performance with or without AI assistance.

6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) Was Done

Yes, a standalone performance study was done. The VITEK® 2 system is a "Fully Automated Short-Term Incubation Cycle Antimicrobial Susceptibility System," and its performance was evaluated against the CLSI broth microdilution reference method. This is an evaluation of the algorithm's output (MIC values and interpretive categories) without direct human intervention in the interpretation of the VITEK® 2 results.

7. The Type of Ground Truth Used

The type of ground truth used is the broth microdilution reference method, specifically the CLSI method incubated at 16-20 hours. This is typically considered the gold standard for antimicrobial susceptibility testing.

8. The Sample Size for the Training Set

The document does not explicitly state the sample size for the training set. The study describes "external evaluation" for performance, but it doesn't separate out a specific training set size for the VITEK® 2 algorithm itself.

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

The document does not explicitly state how the ground truth for any training set was established, as it primarily focuses on the performance evaluation of the final device against a reference method. However, given that the device is an "Automated quantitative antimicrobial susceptibility test," it's highly probable that any internal training/development would have used an established reference method (like broth microdilution) to establish ground truth for algorithm development.

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