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VITEK® 2 Gram Negative Trimethoprim/sulfamethoxazole is designed for antimicrobial susceptibility testing of Gram-negative bacilli. VITEK 2 Gram Negative Trimethoprim/ sulfamethoxazole is a qualitative test 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. Trimethoprim/sulfamethoxazole 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

Escherichia coli (including susceptible enterotoxigenic strains implicated in traveler's diarrhea) Klebsiella species Proteus mirabilis Enterobacter species Shigella flexneri Morganella morganii Shigella sonnei Proteus vulgaris

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

The antimicrobial presented in VITEK 2 AST Cards is in concentrations equivalent by efficacy to standard method concentrations in mcg/ml. The VITEK 2 AST Cards are essentially miniaturized versions of the doubling dilution technique for determining the minimum inhibitory concentration (MIC) microdilution methodology.

The bacterial 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 System 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 cycle, a report is generated that contains the MIC value along with the interpretive category result for each antibiotic contained on the card.

Here's a breakdown of the acceptance criteria and study information for the VITEK® 2 Gram Negative Trimethoprim/sulfamethoxazole (SXT) device, based on the provided text:

1. Table of Acceptance Criteria and Reported Device Performance

Note: The document states that the device demonstrated "substantially equivalent performance when compared with the CLSI 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 February 5, 2003." This guidance document would contain the specific numerical acceptance criteria.

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

• Sample Size: Not explicitly stated as a numerical count of isolates. The text mentions "fresh clinical isolates and stock challenge strains."
• Data Provenance: Not explicitly stated (e.g., country of origin). The study was an "external evaluation." It is common for these types of studies to be multi-center and potentially international, but this document does not specify. The data included both "fresh clinical isolates" (prospective or recent retrospective) and "stock challenge strains."

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

• Number of Experts: Not specified.
• Qualifications of Experts: Not specified. The reference method, CLSI broth microdilution, is a standardized laboratory method, so the "experts" would likely be trained microbiologists or laboratory technicians performing this gold standard method.

4. Adjudication Method for the Test Set

• Adjudication Method: Not applicable in the traditional sense. The ground truth was established by the CLSI broth microdilution reference method, which is a standardized quantitative method that produces a definitive result (MIC value). Discrepancies would be resolved by retesting or further investigation according to laboratory protocols, rather than expert adjudication.

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

• No, an MRMC comparative effectiveness study was not done. This device is an automated antimicrobial susceptibility test system, not an imaging or diagnostic device requiring human interpretation of results. The comparison was between the automated system's results and a reference laboratory method (CLSI broth microdilution).

6. If a Standalone Performance Study Was Done

• Yes, a standalone study was done. The study evaluated the VITEK 2 Gram Negative SXT device's performance (algorithm only) by comparing its results directly to the CLSI broth microdilution reference method. This assesses the algorithm's accuracy without human intervention influencing the result.

7. The Type of Ground Truth Used

• Type of Ground Truth: The ground truth was established by the CLSI broth microdilution reference method. This is considered a gold standard laboratory method for determining minimum inhibitory concentrations (MICs) of antimicrobials.

8. The Sample Size for the Training Set

• Sample Size: Not specified. The document only discusses the "external evaluation" for performance assessment. Information about the training set size is not provided in this 510(k) summary.

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

• How Ground Truth for Training Set Was Established: Not specified. As the training set information is not provided, neither is the method for establishing its ground truth.

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