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chromID™ VRE agar is a selective and differential chromogenic medium containing 8 µg/mL of vancomycin, for the qualitative detection of Enterococcus faecium and E. faecalis showing acquired vancomycin resistance (VRE) in stool specimens. chromID™ VRE agar can be used as an aid to identify, prevent and control VRE colonization in healthcare settings. chromID™ VRE agar is not intended to diagnose VRE infection nor to guide or monitor treatment for infections. Subculture to non-selective media (e.g. trypticase soy agar with 5% sheep blood) is needed for further identification, susceptibility testing and epidemiological typing.

chromID™ VRE agar is a selective chromogenic medium for the detection of E. faecalis showing acquired vancomycin resistance (VRE), in at risk patients. The detection of this resistance is particularly important for the prevention and epidemiological surveillance of these infections and also to prevent the emergence of vancomycin-resistant Staphylococus aureus (VRSA), by t context, the use of chromID™ VRE agar contributes to the active surveillance for VRE agar is a selective and differential chromogenic medium for the qualitative detection of E. faecalis showing acquired vancomycin resistance (VRE), from stool specimens.

chromID™ VRE agar consists of a rich nutritive base including a variety of peptones. It also contains two chromogenic substrates and a mixture of antibiotics including vancomycin (8 ug/mL) which enable the specific and selective growth of VRE. After 24-48 hours incubation vancomycin-resistant E. faecium colonies are a violet color for ß-galactosidase-producing strains. Vancomycin-resistant E. faecalis colonies are a blue-to-green color for a-ducosidase-producing strains. The selective components in the medium inhibit enterpooccal strains that do not express acquired vancomycin resistance, enterococcal strains that express natural intinsic vancomycin resistance (vanC phenotype: E. gallinarum and E. casselflavus), as well as most Gram-negative and Gram-positive bacteria.

Below is an analysis of the provided text regarding the chromID™ VRE Agar, outlining acceptance criteria and supporting study details.

1. Table of Acceptance Criteria and Reported Device Performance

The document does not explicitly state pre-defined acceptance criteria (e.g., "The device must achieve at least X% sensitivity and Y% specificity"). However, it does present performance metrics against which an implicit acceptance was made for 510(k) clearance.

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

• Sample Size: A total of 1299 stool samples were evaluated in the primary performance study.
• Data Provenance: The study was conducted at four geographically diverse laboratories, implying multi-site data collection, which is generally considered robust. The document does not specify the country of origin, but given the submitter's address (Missouri, USA) and the FDA submission, it implicitly refers to data collected in the US or internationally for a US submission. It is a prospective study as specimens were "inoculated" on the media for evaluation, indicating a forward-looking collection and analysis.

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

The document does not specify the number or qualifications of experts involved in establishing the ground truth. It details the methods used for ground truth confirmation rather than the human assessors:

• Gram stain
• Catalase
• VITEK® 2 GP
• 16S-500 sequencing
• Vancomycin resistance confirmed by agar dilution

These methods represent a "conventional reference method" rather than a consensus established by a panel of human experts.

4. Adjudication Method for the Test Set

The document does not describe an adjudication method in the context of human expert disagreement. The ground truth was established by a combination of laboratory tests. For the performance comparisons, the device's results were directly compared against the outcomes of these established laboratory methods.

5. 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

No MRMC comparative effectiveness study was done. This device is a culture medium, not an AI or imaging diagnostic tool that would typically involve human readers interpreting AI-assisted outputs. The performance is based on direct observation of colony color and growth on the agar.

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

Yes, a standalone performance study was done. The chromID™ VRE agar's performance in detecting VRE was evaluated directly by observing the growth and colony characteristics after incubation. This is an "algorithm only" type of assessment in the sense that the medium itself acts as the diagnostic "algorithm" that produces a visible result without mandatory human interpretation of complex data (beyond simple color/growth observation). The study compared the chromID™ VRE agar's outputs against conventional microbiological methods.

7. The Type of Ground Truth Used

The ground truth used was a combination of conventional microbiological identification and antimicrobial susceptibility testing methods:

• Gram stain
• Catalase
• VITEK® 2 GP (for species identification)
• 16S-500 sequencing (for species identification)
• Vancomycin resistance confirmed by agar dilution (the gold standard for vancomycin resistance).

This represents a robust, multi-faceted approach to establishing ground truth for microbial identification and resistance.

8. The Sample Size for the Training Set

The document does not describe a "training set" in the context of an AI/machine learning model. For traditional diagnostic assays like culture media, there isn't typically a distinct training set in the AI sense. However, the development of the chromID™ VRE agar would have involved extensive laboratory work and testing of various formulations and indicators before it reached the validation stage described in the performance section.

• Challenge Testing: 75 well-characterized challenge strains were used to evaluate expected results.
• Low-level resistance testing: 49 enterococci strains with intermediate or low vancomycin resistance were evaluated.
• Cross-reactivity study: 99 organisms were included.

These studies, while not explicitly "training sets," serve a similar purpose in device development and characterization prior to clinical validation.

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

Given that there isn't a "training set" in the AI sense, the ground truth for the various developmental and characterization studies (challenge testing, low-level resistance, cross-reactivity) would have been established through well-defined, standard phenotypic and genotypic microbiological methods, similar to or more extensive than those used for the main performance study (e.g., standard culture, biochemical tests, molecular methods for identification, and MIC determination for resistance). For example, the challenge strains are described as "well-characterized," implying their identity and resistance profiles were already known through such reference methods.

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