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The MicroScan® Dried Gram-Positive MIC/Combo Panel is used to determine quantitative and/or qualitative antimicrobial agent susceptibility of colonies grown on solid media of rapidly growing aerobic and facultative anaerobic gram-positive bacteria. After inoculation, panels are incubated for 16 - 20 hours at 35°C +/- 1°C in a non-CO2 incubator, and read either visually or with MicroScan instrumentation, according to the Package Insert.

This particular submission is for the addition of the antimicrobial Tigecycline at concentrations of 0.12 - 8 mcg/ml to the test panel. MicroScan® Dried Gram-Positive Tigecycline is a qualitative test.

Tigecycline has been shown to be active against the organisms listed below according to the FDA label for the antimicrobial.

Active in vitro and in clinical infections:

Enterococcus faecalis (vancomycin-susceptible isolates) Staphylococcus aureus (methicillin-susceptible and -resistant isolates)

Active in vitro but clinical significance unknown: Staphylococcus epidermidis (methicillin-susceptible and -resistant isolates)

MicroScan Dried Gram-Positive MIC/Combo Panels are designed for use in determining quantitative and/or qualitative antimicrobial agent susceptibility of colonies grown on solid media of rapidly growing aerobic and facultative anaerobic gram-positive bacteria.

The antimicrobial susceptibility tests are miniaturizations of the broth dilution susceptibility test that have been diluted in broth and dehydrated. Various antimicrobial agents are diluted in broth to concentrations bridging the range of clinical interest. Panels are rehydrated with water after inoculation with a standardized suspension of the organism. After incubation in a non-CO2 incubator for 16-20 hours, the minimum inhibitory concentration (MIC) for the test organism is read by determining the lowest antimicrobial concentration showing inhibition of growth.

The MicroScan® Dried Gram-Positive MIC/Combo Panels with Tigecycline (0.12-8 mcg/ml) is a medical device designed to determine antimicrobial agent susceptibility. The device's performance was evaluated against a CLSI frozen Reference Panel to demonstrate substantial equivalence, as defined in the FDA document "Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA."

Here's a breakdown of the acceptance criteria and study details:

1. Table of Acceptance Criteria and Reported Device Performance

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

• Test Set Sample Size: The document mentions "fresh and stock Efficacy isolates and stock Challenge strains." However, the exact number of isolates/strains used in the external evaluation (test set) is not explicitly stated in the provided text.
• Data Provenance: The data was collected during an "external evaluation" designed to confirm acceptability. The specific country of origin is not mentioned, but it can be inferred that it aligns with FDA submission requirements, likely involving clinical or reference laboratories within the United States or equivalent international standards. The study appears to be retrospective in the sense that stock isolates and challenge strains were used, although fresh isolates were also included.

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

The document states the device's performance was compared to a "CLSI frozen Reference panel" and "Expected Results determined prior to the evaluation" for challenge strains. This implies that the ground truth for antimicrobial susceptibility was established through a standardized, well-defined method (likely CLSI M7 guidelines for broth microdilution) rather than relying on individual expert consensus.

• Number of Experts: Not applicable in the traditional sense of a consensus panel, as a CLSI frozen Reference Panel and pre-determined "Expected Results" were used as the gold standard.
• Qualifications of Experts: The CLSI (Clinical and Laboratory Standards Institute) methods themselves are developed by panels of experts in microbiology, infectious diseases, and laboratory medicine. However, the document does not specify individual experts for establishing the ground truth for this particular study.

4. Adjudication Method for the Test Set

The establishment of ground truth was based on comparison to a "CLSI frozen Reference panel" and "Expected Results" for challenge strains. This suggests a direct comparison method rather than an adjudication process among human readers.

• Adjudication method: None in the context of human reader disagreement, as the ground truth was a standardized reference method.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study was Done, and Effect Size

• MRMC Study: No, a multi-reader multi-case comparative effectiveness study was not done. This study focuses on the performance of an automated/semi-automated AST system against a reference method, not on the improvement of human readers with AI assistance.

• Effect Size: Not applicable, as no MRMC study was conducted.

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

• Standalone Study: Yes, the evaluation conducted was a standalone study of the device. The MicroScan Dried Gram-Positive MIC/Combo Panel, either read visually or with MicroScan instrumentation (autoSCAN®-4 and WalkAway®), operates as an algorithm/system to determine MIC values and categorical interpretations. Its performance was compared directly to a "CLSI frozen Reference panel" and "Expected Results," which represents its standalone capability without direct human interpretation being part of the primary performance metric for substantial equivalence (though human reading is an option for panel interpretation).

7. The Type of Ground Truth Used

• Ground Truth Type: The ground truth used was established by a CLSI frozen Reference Panel and pre-determined expected results for challenge strains. This is a highly standardized and well-accepted method for determining antimicrobial susceptibility, considered the gold standard in microbiology. It is essentially a form of reference standard data based on established protocol outcomes.

8. The Sample Size for the Training Set

The provided text does not contain any information about a specific training set or its sample size. This type of device (Microdilution MIC Panels) is typically developed based on established microbiological principles and validated against reference methods, rather than being a machine learning model that requires a discrete training set in the modern sense. The "development" would involve optimizing panel concentrations and reading algorithms.

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

Since no specific training set is mentioned as part of a machine learning paradigm, the establishment of ground truth for a "training set" is not applicable as described in the provided text. The overall design and optimization of such panels are based on extensive antimicrobial susceptibility testing literature, CLSI guidelines, and internal research and development following established microbiological practices.

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