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The BD Phoenix Automated Microbiology System is intended for in vitro quantitative determination of antimicrobial susceptibility by minimal inhibitory concentration (MIC) of most Gram-negative aerobic and facultative anaerobic bacteria isolates from pure culture for Enterobacterales and Non-Enterobacterales and most Gram-positive bacteria isolates from pure culture belonging to the genera Staphylococcus, Enterococcus, and Streptococcus.

This premarket notification is for the BD Phoenix Automated Microbiology System with Eravacycline at a concentration of 0.125-2 µg/mL. Testing is indicated for Enterobacterales as recognized by the FDA Susceptibility Test Interpretive Criteria (STIC).

The BD Phoenix Automated Microbiology System - GN Eravacycline (0.125-2 µg/mL) has demonstrated acceptable performance with the following organisms:

Enterobacterales (Citrobacter amalonaticus, Citrobacter braakii, Citrobacter farmeri, Citrobacter freundii, Citrobacter koseri, Citrobacter youngae, Enterobacter cloacae, Escherichia coli, Klebsiella aerogenes, Klebsiella oxytoca, and Klebsiella pneumoniae)

This submission is for addition of Eravacycline (0.125-2 µg/mL) to the BD Phoenix™ ID/AST or AST only panels. The ID portion of the ID/AST combination panel was not subject to review in this submission.

The Phoenix AST method is a broth-based microdilution test. The Phoenix panel is a sealed and self-inoculating molded polystyrene tray with 136 micro-wells containing dried reagents. The ID/AST combination panel includes an ID side (51 wells) with dried substrates for bacterial identification and an AST side (85 wells). The AST panel contains a wide range of two-fold doubling dilution concentrations of antimicrobial agents and growth and fluorescent controls at appropriate well locations. The AST panel does not include wells for isolate identification.

The Phoenix System utilizes a redox indicator for the detection of organism growth in the presence of an antimicrobial agent. The organism to be tested must be a pure culture and be preliminarily identified as Gram-positive or Gram-negative. Colonies are then suspended in ID broth and equated to a 0.5 McFarland suspension using a nephelometer device. A further dilution is made into AST broth (a cation-adjusted formulation of Mueller-Hinton broth containing 0.010% Tween 80), to which the redox-buffered oxidation-reduction AST indicator solution is added producing a blue color in the wells. The concentration of organisms in the final AST broth suspension is approximately 5 X 10⁵ CFU/mL.

The Phoenix AST Broth is poured into the inoculation port of the AST panel and the inoculum flows into the panel, filling panel wells. Polyethylene caps are applied to seal the inoculation ports. An air admittance port is located in the panel lid to ensure adequate oxygen tension in the panel for the duration of the test. Inoculated panels are barcode scanned and loaded into the BD Phoenix Automated Microbiology System instrument where panels are continuously incubated at 35 °C ± 1 °C.

Continuous measurements of changes to the indicator as well as bacterial turbidity are used in the determination of bacterial growth. The instrument takes readings every 20 minutes. Organisms growing in the presence of a given antimicrobial agent reduce the indicator (changing it to a pink color). This signals organism growth and resistance to that antimicrobial agent. Organisms killed or inhibited by the antimicrobial agent do not cause reduction of the indicator and therefore do not produce a color change. The Phoenix instrument reads and records the results of the antimicrobial tests contained in the panel and interprets the reactions (based on the organism identification) to give a minimal inhibitory concentration (MIC) value and category interpretations (susceptible, intermediate, resistant, or not susceptible). AST results are available within 16 hours.

This is an auto read result; no manual readings are possible with this system.

Additional comments concerning specific organism/antimicrobial combinations are provided from the software-driven expert system (BDXpert), using rules derived from CLSI documentation and/or the FDA-approved drug labeling.

Here's a breakdown of the acceptance criteria and the study details for the BD Phoenix Automated Microbiology System - GN Eravacycline (0.125-2 µg/mL), based on the provided FDA 510(k) clearance letter:

1. Table of Acceptance Criteria and Reported Device Performance

Note on VMEs: A very major error (VME) occurs when a resistant isolate is categorized as susceptible by the device. This is a critical error as it can lead to inappropriate treatment. The FDA's acceptable rate for adjusted VMEs is typically ≤ 1.5%. The device exceeded this threshold for combined clinical and challenge isolates with manual inoculation, and for challenge isolates with manual inoculation, which required specific cautionary statements and recommendations for confirmatory testing in the product labeling.

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

• Clinical Isolates: 785 isolates (626 fresh, 159 stock)
  • Provenance: "three U.S. sites" (presumably clinical laboratories in the US). The exact country of origin for the isolates themselves is not specified beyond "U.S. sites."
  • Retrospective/Prospective: Not explicitly stated, but "fresh" and "stock" isolates suggest a mix, likely collected over time (retrospective component for stock, and potentially prospective for fresh if collected specifically for the study, or recent retrospective).
• Challenge Isolates: 84 isolates (stock isolates with known resistance mechanisms).
  • Provenance: "Additional stock challenge isolates were tested at each study site." (three U.S. sites, as mentioned for clinical testing).
  • Retrospective/Prospective: Retrospective (stock isolates).
• Reproducibility Isolates: 12 on-scale isolates.
• Quality Control Isolates: E. coli ATCC 25922 and P. aeruginosa ATCC 27853 (standard ATCC strains).

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

The ground truth for the test set (both clinical and challenge isolates) was established using the CLSI frozen broth microdilution reference panel, prepared according to CLSI M07 guidelines. This is a standardized laboratory method, not reliant on individual human experts in the same way, for example, a radiology image interpretation study would be. Therefore, the concept of "number of experts" and their "qualifications" doesn't directly apply in this context. The "expert" in this case is the CLSI standard method itself, which is developed by committees of microbiology experts.

4. Adjudication Method for the Test Set

Not applicable in the traditional sense of multiple human readers or a consensus process. The reference method (CLSI frozen broth microdilution) serves as the "gold standard" or ground truth. Discrepancies between the device and the reference method were analyzed for Essential Agreement (EA) and Category Agreement (CA). Further analysis and "adjustments" for major and very major errors were based on whether the MIC values of the errors fell within essential agreement (i.e., within one doubling dilution of the reference method).

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

No, a Multi-Reader Multi-Case (MRMC) comparative effectiveness study was not done. This type of study is typically used for diagnostic devices that involve human interpretation (e.g., radiologists reading images) to compare the performance of human readers with and without AI assistance. The BD Phoenix system is an automated platform for antimicrobial susceptibility testing, where human interpretation of results is minimal once the system produces MIC values and interpretations.

6. Standalone Performance Study

Yes, a standalone performance study was done. The entire study described, which compares the BD Phoenix Automated Microbiology System's results directly against the CLSI frozen broth microdilution reference method, represents the standalone performance of the algorithm/device without human-in-the-loop performance influencing the primary results. The system automatically reads and interprets the results.

7. Type of Ground Truth Used

The type of ground truth used was a reference method, specifically the CLSI frozen broth microdilution reference panel prepared according to CLSI M07 guidelines. This is considered the "gold standard" for antimicrobial susceptibility testing.

8. Sample Size for the Training Set

The document does not explicitly mention a separate training set or its sample size. This is common for predicate-based 510(k) submissions, where the focus is on demonstrating substantial equivalence to a legally marketed predicate device, and the "training" of the internal device algorithms might have occurred during its initial development or earlier predicate clearances. The performance data presented here are for validation and comparison against the reference method.

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

As no specific training set is mentioned, the method for establishing its ground truth is also not described. If the device uses machine learning, its initial development and training would typically involve large datasets with ground truth established by expert-reviewed reference methods. However, this clearance focuses on the validation of a specific addition (Eravacycline) to an already established system.

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