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The BD Phoenix™ Automated Microbiology System is intended for the rapid identification and in vitro antimicrobial susceptibility testing of isolates from pure culture of most aerobic and facultative anaerobic Gram-negative and Gram-positive bacteria of human origin.

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 Enterobacteriaeae and Non-Enterobacteriaeae and Gram-positive bacteria isolates from pure culture belonging to the genera Staphylococcus and Enterococcus.

This premarket notification is for the addition of the antimicrobial agent Cefazolin at concentrations of 2-32 µg/mL to Gram Positive ID/AST or AST only Phoenix panels. Cefazolin has been shown to be active in vitro and in clinical infections against: Staphylococcus aureus (including penicillinase-producing strains) and Staphylococcus epidermidis.

The BD Phoenix Automated Microbiology System (Phoenix System) is an automated system for the rapid identification (ID) and antimicrobial susceptibility testing (AST) of clinically relevant bacterial isolates. The system includes the following components:

• BD Phoenix instrument and software.
• BD Phoenix panels for organism ID testing and antimicrobial agents for AST determinations.
• BD Phoenix ID Broth used for performing ID tests and preparing AST Broth inoculum.
• BD Phoenix AST Broth used for performing AST tests only.
• BD Phoenix AST Indicator solution added to the AST Broth to aid in bacterial growth determination.

The Phoenix panel is a sealed and self-inoculating molded polystyrene tray with 136 micro-wells containing dried reagents. Organisms for susceptibility testing must be a pure culture and preliminary identification as a Gram-negative or Gram-positive isolate. For each isolate, an inoculation suspension equivalent to a 0.5 McFarland standard is prepared in Phoenix ID broth.

The Phoenix AST method is a broth based microdilution test. The Phoenix system utilizes a redox indicator for the detection of organism growth in the presence of an antimicrobial agent. Measurements of changes to the indicator as well as bacterial turbidity are used in the determination of organism growth. The Phoenix panels contain various antimicrobial agents with a wide range of two-fold doubling dilution concentrations.

The instrument houses the panels where they are continuously incubated at a nominal temperature of 35 degrees Celsius. The instrument takes readings of the panels every 20 minutes. The readings are interpreted to give an identification of the isolate, minimum inhibitory concentration (MIC) values and category interpretations, S, I, or R (sensitive, intermediate, or resistant).

Acceptance Criteria and Study Details for BD Phoenix™ Automated Microbiology System - Cefazolin 2-32 µg/mL

1. Table of Acceptance Criteria and Reported Device Performance

The provided document defines the acceptance criteria in terms of "Essential Agreement (EA)" and "Category Agreement (CA)" with the NCCLS reference broth microdilution method. The performance is summarized in Table 1.

Note: While specific numeric acceptance criteria (e.g., "EA > 95%") are not explicitly listed in the provided text, the conclusion that the device "demonstrates substantially equivalent performance" based on the observed 100% EA and CA strongly implies that these results met the internal or regulatory acceptance thresholds for substantial equivalence under the FDA Draft guidance document, "Guidance on Review Criteria for Assessment of Antimicrobial Susceptibility Devices," March 8, 2000.

2. Sample size used for the test set and the data provenance

• Sample Size for Test Set: 507 isolates (n=507) of Gram-positive organisms.
• Data Provenance:
  • Country of Origin: United States. The study states, "Clinical, stock and challenge isolates were tested across multiple geographically diverse sites across the United States."
  • Retrospective or Prospective: Not explicitly stated as retrospective or prospective for the clinical isolates. However, the testing of "stock and challenge isolates" alongside "clinical isolates" suggests a methodology that combines existing collections (stock/challenge, which could be considered retrospective or curated) with potentially newly acquired clinical isolates (prospective or concurrent). The overall context of a premarket study for a new antimicrobial agent addition to an existing system often involves a mix to ensure comprehensive evaluation.

3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts

The document does not specify the number of experts or their qualifications. The "ground truth" (reference results) was established using the NCCLS reference broth microdilution method. This method is a standardized laboratory procedure, not typically dependent on expert interpretation for establishing the result itself, but rather on adherence to the protocol by trained laboratory personnel.

4. Adjudication method for the test set

The document does not describe an adjudication method involving multiple human readers or experts for the test set. The comparison was made between the BD Phoenix System results and the results obtained from the NCCLS reference broth microdilution method, which is a direct, standardized laboratory assay.

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, a multi-reader, multi-case (MRMC) comparative effectiveness study was not done.

This device (BD Phoenix Automated Microbiology System) is an automated system for antimicrobial susceptibility testing, which provides automated results (MIC values and categorical interpretations). It does not involve human "readers" interpreting images or clinical data where AI assistance would be applicable in the typical sense of an MRMC study for imaging or clinical decision support. The system is the "AI" (or automated algorithm) that performs the test and provides the interpretation.

6. If a standalone (i.e. algorithm only without human-in-the-loop performance) was done

Yes, a standalone performance study was done.

The entire study described is a standalone performance evaluation of the "BD Phoenix™ Automated Microbiology System" (the device/algorithm) against the reference method. The system inherently operates as an "algorithm only" in generating the MIC and susceptibility category interpretations. There is no mention of a human-in-the-loop component being evaluated or integrated into the performance claims for this specific study; the device itself provides the final result.

7. The type of ground truth used

The type of ground truth used was NCCLS reference broth microdilution method. This is a laboratory reference standard (gold standard biological assay) for determining antimicrobial susceptibility, widely accepted in microbiology.

8. The sample size for the training set

The document does not specify a separate "training set" or its sample size. The description focuses on the validation of the Cefazolin agent on the existing BD Phoenix system. Automated microbiology systems typically rely on pre-established algorithms and decision rules derived from extensive historical data and expert panels during their initial development. The current submission is for an addition of an antimicrobial agent to an already established system, so the performance evaluation is focused on the new agent's accuracy with the existing system, rather than a de novo algorithm training.

9. How the ground truth for the training set was established

As no separate "training set" is explicitly mentioned for this specific submission, the method for establishing its ground truth is not provided in the document. For the development of the core BD Phoenix system itself, ground truth for algorithm training would have historically been established through extensive testing against reference methods like NCCLS broth microdilution, often corroborated with expert microbiological interpretation over many years of data collection.

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