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The MicroScan Synergies plus™ Gram-Negative 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-negative bacilli. After inoculation, panels are incubated for 4.5 - 18 hours at 35°C +/- 1°C, in a WalkAway SI or equivalent, and read by the MicroScan® Instrumentation. Additionally, the panels may be incubated in a non-CO2 incubator and the AST portions can be read visually, according to the Package Insert.

This particular submission is for the addition of the antimicrobial Nitrofurantoin, at concentrations of 1 to 256 ug/ml, to the test panel.

The gram-negative organisms which may be used for Nitrofurantoin susceptibility testing in this panel are:

Escherichia coli Citrobacter amalonaticus Citrobacter freundii Citrobacter koseri (diversus) Klebsiella oxytoca Klebsiella ozaenae Klebsiella spp. * Enterobacter spp. *

• Some strains of Klebsiella species and Enterobacter species are resistant to Nitrofurantoin.

MicroScan® rapID/S plus™ Gram-Negative 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-negative bacilli.

The antimicrobial susceptibility tests are miniaturizations of the broth dilution susceptibility test that have been diluted in Mueller-Hinton 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 the WalkAway® SJ System, or equivalent, for 4.5 - 18 hours, the minimum inhibitory concentration (MIC) for the test organism is read by determining the lowest antimicrobial concentration showing inhibition of growth.

The provided text describes the 510(k) submission for the MicroScan® Synergies Plus Gram-Negative MIC/Combo Panels with Nitrofurantoin. The device is an antimicrobial susceptibility test system.

Here's an analysis of the acceptance criteria and the study that proves the device meets them, based on the provided text:

1. Table of Acceptance Criteria and Reported Device Performance

Explanation of "Implied" Acceptance Criteria: The document mentions that the device "demonstrated substantially equivalent performance when compared with an NCCLS frozen Reference Panel, as defined in the FDA document 'Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA', dated February 5, 2003." This FDA guidance document would contain the specific acceptance criteria (e.g., percentage for Essential Agreement, Categorical Agreement, etc.). While the exact numerical criteria from the guidance are not explicitly stated in this document, the reported performance of ">99% Essential Agreement" is presented as meeting those criteria.

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

• Test Set Description: The external evaluation was conducted with "fresh and stock Efficacy isolates and stock Challenge strains."
• Sample Size: The exact number of isolates/strains used for the test set is not explicitly stated in the provided text.
• Data Provenance: The text does not specify the country of origin of the data. It indicates the evaluation was "external," meaning performed outside the manufacturer's internal labs, but doesn't detail the location. The study involves "Efficacy isolates" and "Challenge strains," suggesting a mix of clinical relevance and specific strains designed to test performance limits. It is a prospective comparison against a reference method.

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

• The ground truth for the test set was established by comparing the device's performance against an NCCLS frozen Reference Panel.
• The NCCLS (National Committee for Clinical Laboratory Standards, now CLSI) sets standards for antimicrobial susceptibility testing. The "Expected Results" for the "Challenge strains" were "determined prior to the evaluation," implying expert consensus in establishing these reference values.
• The document does not specify the number or qualifications of experts directly involved in establishing the NCCLS frozen Reference Panel or the "Expected Results" for the challenge strains. However, an NCCLS reference panel inherently represents a consensus of experts in the field of clinical microbiology.

4. Adjudication Method for the Test Set

• The adjudication method described is a direct comparison of the MicroScan® rapID/S plus™ Gram-Negative MIC/Combo Panel with Nitrofurantoin against an NCCLS frozen Reference Panel and against "Expected Results" for challenge strains. This is a point-by-point comparison rather than a human reader adjudication method. Therefore, no multi-reader adjudication method (like 2+1 or 3+1) is applicable here.

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

• No, an MRMC comparative effectiveness study involving human readers and AI assistance was not performed or described. This device is an automated antimicrobial susceptibility testing system, and its performance is evaluated against a reference standard, not in the context of human reader improvement.

6. Standalone (Algorithm Only Without Human-in-the-Loop Performance) Study

• Yes, a standalone performance study was performed. The device's performance (ability to determine MICs) was directly compared against the NCCLS frozen Reference Panel and Expected Results for challenge strains, without human intervention affecting the interpretive results of the MicroScan system itself. The text states: "...the minimum inhibitory concentration (MIC) for the test organism is read by determining the lowest antimicrobial concentration showing inhibition of growth" by the MicroScan® system.

7. Type of Ground Truth Used

• The ground truth used was based on NCCLS frozen Reference Panel results and pre-determined "Expected Results" for stock Challenge strains. This is a reference standard method widely accepted in microbiology for establishing the accuracy of antimicrobial susceptibility tests.

8. Sample Size for the Training Set

• The document does not explicitly mention a separate "training set" or its sample size. This type of device's development typically involves extensive internal testing and refinement (which could be considered analogous to training), but the document specifically focuses on the external validation study using "fresh and stock Efficacy isolates and stock Challenge strains" as the evaluation set. It's possible the 'training' or development phase used a different set of isolates not detailed here, or the system's design is based on established biochemical/microbiological principles rather than a machine learning training paradigm requiring a distinct, large 'training set' in the modern AI sense.

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

• As a training set is not explicitly described, the method for establishing its ground truth is not provided. If an internal 'training' process occurred, it would likely also rely on comparison to established reference methods or expert interpretation similar to the NCCLS reference standard.

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