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To determine bacterial antimicrobial agent susceptibility

The MicroScan MICroSTREP plus® Panel is used to determine quantitative and/or qualitative antimicrobial agent susceptibility of colonies grown on solid media of aerobic streptococci, including Streptococcus pneumoniae . After inoculation, panels are incubated for 20 - 24 hours at 35°C +/- 1°C in a non-CO2 incubator, and read visually according to the Package Insert. Additionally, the panels may be incubated in and read by a MicroScan® WalkAway instrument. This particular submission is for the addition of instrument read capability of the antimicrobial Cefaclor, at concentrations of 0.5 to 8 mcg/ml on the MicroScan MICroSTREP plus® Panel. The organisms which may be used for Cefaclor susceptibility testing in this panel are: Streptococcus pneumoniae

The MicroScan MICroSTREP plus® Panel is used to determine quantitative and/or qualitative antimicrobial agent susceptibility of colonies grown on solid media of aerobic streptococci, including Streptococcus pneumoniae. After inoculation, panels are incubated for 20-24 hours at 35°C +/-1 ℃ in a non-CO2 incubator, and read according to the Package Insert.

The antimicrobial susceptibility tests are miniaturizations of the broth dilution susceptibility test. Various antimicrobial agents are diluted in water, buffer or minute concentrations of broth to concentrations bridging the range of clinical interest. Panels are rehydrated with 115 µl Mueller-Hinton broth supplemented with 2-5% lysed horse blood (LHB) and buffered with 50 mM HEPES, after inoculation of the broth with a standardized suspension of the organism in saline. After incubation in a non-CO2 incubator for 20-24 hours, the minimum inhibitory concentration (MIC) for the test organism is manually read by observing the lowest antimicrobial concentration showing inhibition of growth. Additionally, the panels may be incubated in and read by a MicroScan WalkAway instrument.

Acceptance Criteria and Study Details for MicroScan MICroSTREP plus® Panel (Cefaclor)

This submission describes the acceptance criteria and study proving the MicroScan MICroSTREP plus® Panel meets these criteria for determining bacterial susceptibility to Cefaclor using the MicroScan WalkAway instrument.

1. Table of Acceptance Criteria and Reported Device Performance

Note: Essential Agreement (EA) for AST devices typically refers to the percentage of MIC results that are within one doubling dilution of the reference method's MIC result. The FDA guidance document (cited in the submission) specifies the expected thresholds for EA for different AST systems. While the exact threshold isn't explicitly stated in this summary, the 92.5% achieved is reported as "acceptable."

2. Sample Size and Data Provenance for the Test Set

• Sample Size for Test Set: The study was conducted with "stock and CDC Challenge strains." The exact number of strains/isolates is not explicitly stated in the provided text.
• Data Provenance: The external evaluation was conducted as described, implying prospective testing of these strains. The country of origin for the data is not specifically mentioned, but given the manufacturer (Dade Behring Inc.) and FDA submission, it can be inferred to be a US-based or internationally collected set of strains used in a US regulatory context.

3. Number of Experts and Qualifications for Ground Truth

• Number of Experts: Not specified.
• Qualifications of Experts: Not specified. The ground truth was established as "Expected Results determined before the evaluation," and also referenced a "CLSI frozen Reference Panel." This suggests that the ground truth was derived from established reference methods, likely interpreted by qualified microbiologists, but the specifics are not detailed.

4. Adjudication Method for the Test Set

• The text describes the comparison of instrument read results with an "Expected Result generated on a CLSI frozen Reference Panel." This indicates that the CLSI reference panel serves as the gold standard against which the device's performance is measured.
• There is no mention of a traditional expert adjudication (e.g., 2+1, 3+1 consensus) of the device's results. Instead, the device's results are directly compared to the established "Expected Result" from the CLSI reference method.

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

• No, an MRMC comparative effectiveness study was not explicitly done. This study focuses on the mechanical/automated reading of the MicroScan MICroSTREP plus® Panel by the MicroScan WalkAway instrument compared to a defined reference standard ("Expected Result"). The focus is on the instrument's performance, not on direct human reader improvement with or without AI assistance. The original method, to which this instrument-read method is an addition, involves manual reading, but the study described here is not a comparison of human readers with and without the instrument.

6. Standalone Performance Study

• Yes, a standalone study was done. The study's primary objective was to evaluate the "proposed instrument read method" (i.e., the algorithm/instrument's performance without human intervention to interpret the results once the instrument has read them) against a "CLSI frozen Reference Panel" and its "Expected Result." The 92.5% Essential Agreement reflects this standalone performance of the MicroScan WalkAway instrument in reading the panels.

7. Type of Ground Truth Used

• The ground truth used was based on results generated on a CLSI (Clinical and Laboratory Standards Institute) frozen Reference Panel, which is a widely accepted standard for antimicrobial susceptibility testing. These are referred to as "Expected Results determined before the evaluation." This is a highly robust and standardized form of ground truth for this type of in vitro diagnostic device.

8. Sample Size for the Training Set

• Not explicitly stated. The provided summary describes the validation of the instrument-read method, not the development or training of the underlying algorithm for the instrument reading. While the instrument likely incorporates algorithms, no information on a specific "training set" or its size is given in this document.

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

• Not applicable / Not explicitly stated. As noted above, the document focuses on the performance validation rather than the internal development of the instrument's reading capabilities. Therefore, how any "training set" ground truth might have been established for the instrument's internal algorithms is not detailed. The study's focus is on comparing the instrument's output to an independent ground truth reference method.

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