(252 days)
BD BBL™ CHROMagar™ 0157 is a selective medium for the isolation, differentiation and presumptive identification of Escherichia coli 0157:H7 from clinical human stool specimens.
BBL™ CHROMagar™ O157 formulation incorporates chromogenic substrates, which allow colonies of E. coli O157:H7 to produce a mauve color for presumptive identification from the primary isolation plate and differentiation from other organisms. Specially selected Difco™ peptones are incorporated to supply nutrients. The addition of potassium tellurite, cefixime and cefsulodin reduces the number of bacteria other than E. coli O157:H7 that grow on this medium. The chromogen mix consists of artificial substrates (chromogens), which release an insoluble colored compound when hydrolyzed by a specific enzyme. E. coli O157:H7 utilizes one of the chromoqenic substrates producing mauve colonies. The growth of mauve colonies is considered presumptive for E. coli 0157:H7 on BBL™ CHROMagar™ 0157. Non-E. coli O157:H7 bacteria may utilize other chromogenic substrates resulting in blue-green colored colonies or, if none of the chromogenic substrates are utilized, colonies may appear as their natural color. These visually distinct colored colonies facilitate the detection and differentiation of E. coli 0157:H7 from other organisms.
Here's an analysis of the provided text regarding the acceptance criteria and study for the BBL™ CHROMagar™ O157 device:
BBL™ CHROMagar™ O157 Device Study Summary
1. Acceptance Criteria and Reported Device Performance
The direct acceptance criteria are not explicitly stated as numerical thresholds in the provided text. However, the study aims to demonstrate that BBL™ CHROMagar™ O157 performs "as well as" the predicate device (SMAC) and another commercially available medium (SMAC-CT) in presumptively identifying E. coli O157:H7. The results from the external clinical study provide the performance metrics against the predicate device.
Table of Performance:
| Metric | Reported Device Performance (BBL™ CHROMagar™ O157 vs. SMAC) |
|---|---|
| Positive Percent Agreement | 86.4% |
| Negative Percent Agreement | 99.8% |
2. Sample Size and Data Provenance
- Test Set Sample Size: 3,136 stool specimens were initially cultured, with 2,855 providing acceptable results for the study.
- Data Provenance: The external clinical study was conducted at "an external centralized regional clinical laboratory that routinely tests for E. coli O157:H7 in stool specimens." The country of origin is not explicitly stated, but the context (FDA 510(k) submission, Department of Health & Human Services USA) strongly suggests it was conducted in the United States.
- Retrospective or Prospective: The study describes specimens being "inoculated onto Sorital-MacConkey (SMAC) and BBL CHROMagar O157 media," implying a prospective collection and testing of new specimens at the time of the study, rather than analyzing existing archived data.
3. Number of Experts and Qualifications for Ground Truth
- Number of Experts: "Each Plate was read by an independent technologist." The exact number of technologists involved is not specified, but it implies at least two (one for SMAC, one for CHROMagar, though it might have been the same technologist reading both, followed by confirmatory testing). It doesn't appear that multiple experts independently read the same plates to establish a consensus ground truth at the reading stage.
- Qualifications of Experts: The experts are referred to as "independent technologist(s)." Specific qualifications (e.g., years of experience, certifications) are not detailed in the provided text.
4. Adjudication Method for the Test Set
The primary method for establishing the definitive ground truth (beyond the initial technologist reading) was: "confirmatory testing (indole and serotyping) was conducted on all suspected colony samples." This indicates that any suspected positive result from either the SMAC or BBL CHROMagar O157 plates underwent further definitive laboratory testing. This is a form of confirmatory testing adjudication, where definitive lab tests serve as the ultimate arbiter, rather than a consensus among human readers of the primary plates.
5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study
No, a multi-reader multi-case (MRMC) comparative effectiveness study was not conducted in the typical sense of measuring human reader improvement with or without AI assistance. This device is a culture medium, not an AI-powered diagnostic tool for interpretation. The comparison is between the BBL™ CHROMagar™ O157 medium and predicate media, both of which are interpreted manually by a technologist.
6. Standalone Performance Study
Yes, a standalone study was performed in the sense that the performance of the BBL™ CHROMagar™ O157 medium was evaluated independently. The "External Studies" section details its performance (Positive Percent Agreement and Negative Percent Agreement) in comparison to the SMAC medium based on the final confirmatory testing. The "Internal Studies" also included a Limit of Detection study and a cross-reactivity study, which assess the medium's inherent performance.
7. Type of Ground Truth Used
The ground truth used for the external clinical study was primarily confirmatory laboratory testing, specifically "indole and serotyping" performed on "all suspected colony samples." This represents a high-level, definitive laboratory identification of E. coli O157:H7.
8. Sample Size for the Training Set
The document does not mention a training set size. This is because the BBL™ CHROMagar™ O157 is a traditional in-vitro diagnostic culture medium, not a machine learning or artificial intelligence algorithm that requires a training set.
9. How Ground Truth for the Training Set Was Established
As there is no training set for this type of device, this question is not applicable. The device's formulation and chromogenic properties are based on biological principles, not on learned patterns from a dataset.
§ 866.2360 Selective culture medium.
(a)
Identification. A selective culture medium is a device that consists primarily of liquid or solid biological materials intended for medical purposes to cultivate and identify certain pathogenic microorganisms. The device contains one or more components that suppress the growth of certain microorganisms while either promoting or not affecting the growth of other microorganisms. The device aids in the diagnosis of disease caused by pathogenic microorganisms and also provides epidemiological information on these diseases.(b)
Classification. Class I (general controls). The device is exempt from the premarket notification procedures in subpart E of part 807 of this chapter subject to the limitations in § 866.9.