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VITEK® 2 Streptococcus Tetracycline 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 Tetracycline is a quantitative test. Tetracycline has been shown to be active against the microorganisms listed below, according to the FDA label for this antimicrobial.

Active in vitro and in clinical infections: Streptococcus pneumoniae Streptococcus pyogenes*

*The VITEK® 2 Streptococcus Susceptibility Card also reports the susceptibility of the following additional organisms as listed on the FDA Susceptibility Test Interpretative Criteria website (STIC): Streptococcus spp. B-Hemolytic Group (other than S. pyogenes).

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 Streptococcus 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 Tetracycline has the following concentrations in the card: 0.125, 0.5, 1, and 4 ug/mL (equivalent standard method concentration by efficacy in ug/mL).

Here's an analysis of the acceptance criteria and study proving the device meets those criteria, based on the provided text:

Device: VITEK® 2 Streptococcus Tetracycline (≤0.25 - ≥16 µg/mL)
Intended Use: Antimicrobial susceptibility testing of Streptococcus species, as a laboratory aid in determining in vitro susceptibility to antimicrobial agents. Specifically for Streptococcus pneumoniae and Streptococcus pyogenes, with additional reporting for Beta-hemolytic Streptococcus (other than S. pyogenes).

Acceptance Criteria and Reported Device Performance

The study compared the VITEK® 2 Streptococcus Tetracycline performance against the CLSI broth microdilution reference method. The acceptance criteria are implicitly defined by the guidance document cited: "FDA Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA (Issued August 28, 2009)."

Note on N/A for VME/ME: The table explicitly states "N/A" for VME and ME for S. pneumoniae and S. pyogenes. This often happens when there are no resistant isolates in the sample set or too few to reliably calculate these error rates, or if the "N/A" rather indicates that essential and categorical agreements are sufficient and the specific error rates are not the primary metrics for that specific organism set. However, for Beta-hemolytic Streptococcus, VME, ME, and mE percentages are provided, suggesting these metrics were relevant for that group.

Study Details

1. Sample sizes used for the test set and the data provenance:

   • Test Set Sample Sizes:
     • Streptococcus pneumoniae: 289 isolates
     • Streptococcus pyogenes: 308 isolates
     • Beta-hemolytic Streptococcus (other than S. pyogenes): 530 isolates
   • Total Isolates: 289 + 308 + 530 = 1127 isolates
   • Data Provenance: The study involved 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 whether the study was retrospective or prospective. Typically, clinical isolates imply prospective collection from various clinical labs in the country where the study was primarily conducted (likely the US, given FDA submission).

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

   • Not applicable in this context. The ground truth for antimicrobial susceptibility testing (AST) is established by a standardized, physical reference method, not by expert consensus on interpretations of images or signals. The reference method used was the CLSI broth microdilution reference method.

3. Adjudication method for the test set:

   • Not applicable. As the ground truth is established by a standardized laboratory method (broth microdilution), there's no need for human adjudication of results in the traditional sense. The comparison is between the device's output and the reference method's output.

4. 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:

   • Not applicable. This is not an AI/imaging device. It's an automated antimicrobial susceptibility testing system. The "readers" are the instruments (VITEK® 2 and VITEK® 2 Compact Systems) which produce quantitative results (MIC) and interpretive categories (Susceptible, Intermediate, Resistant).

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

   • Yes, the performance listed in Table 2 (Essential Agreement and Category Agreement) represents the standalone performance of the VITEK® 2 system compared to the reference method. The device is designed to provide automated results.

6. The type of ground truth used:

   • Reference Method: The ground truth was established using the CLSI broth microdilution reference method, incubated at 16-24 hrs. This is a well-established and standardized laboratory method for determining minimum inhibitory concentrations (MICs) of antimicrobials.

7. The sample size for the training set:

   • The document implies that the study described is a validation study used to support regulatory submission, not a study that involved a training phase for a machine learning model. Therefore, a "training set" in the context of AI is not relevant here. The device uses "Discriminant Analysis" algorithms, which would have been developed and validated internally during the device's original development, not as part of this specific 510(k) submission. No training set size is provided for the algorithms themselves.

8. How the ground truth for the training set was established:

   • Not applicable, as this is not an AI/ML development study presented in the document. The "ground truth" for developing the underlying discriminant analysis algorithms (mentioned as the "Analysis Algorithms") would have traditionally been established using similar reference methods during the initial R&D phase of the VITEK® 2 system itself.

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