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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 Enterobacteriaceae and Non-Enterobacteriaceae and most 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 cephalothin at concentrations of 0.5-64 µg/mL to Gram Positive ID/AST or AST only Phoenix panels.

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.
• DD Phoenix panels containing biochemicals for organism ID testing and antimicrobial agents or 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 reagens. Organisms for susceptibility testing must be a pure culture and preliminarily identified as a Gram-negative or Gram-positive isolate. For each isolate, an inoculation 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 and to bacterial turbidity are used in the determination of MIC values. The AST panel contains several 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 C. 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).

The following information describes the acceptance criteria and the study that proves the device meets the acceptance criteria for the BD Phoenix™ Automated Microbiology System - Cephalothin 0.5-64 µg/mL.

1. Table of Acceptance Criteria and Reported Device Performance

Note: The FDA guidance "Guidance on Review Criteria for Assessment of Antimicrobial Susceptibility Devices", March 8, 2000, would define the specific numerical acceptance criteria for EA and CA, though those percentages are not explicitly stated in this summary.

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

• Test Set Sample Size: 1220 isolates for Cephalothin.
• Data Provenance: Clinical, stock, and challenge isolates were tested across multiple geographically diverse sites across the United States. The study incorporated both clinical isolates and challenge set isolates. The summary does not explicitly state if the data was retrospective or prospective, but clinical trials are generally prospective in nature.

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

The document does not explicitly state the number or qualifications of experts used to establish the ground truth for the test set. However, the ground truth was established by comparison to the NCCLS reference broth microdilution method for susceptibility testing and "expected results" for clinical isolates. This implies that the reference method itself, conducted by trained laboratory personnel, served as the 'ground truth' rather than a panel of individual experts rendering interpretations.

4. Adjudication method for the test set

The document does not describe an explicit adjudication method for the test set beyond comparing results to the NCCLS reference method and "expected results." Discrepancies between the device and the reference method would be analyzed in terms of Essential Agreement and Category Agreement, but a formal adjudication process (e.g., 2+1, 3+1) is not detailed.

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

A multi-reader multi-case (MRMC) comparative effectiveness study was not conducted. This device is an automated system for antimicrobial susceptibility testing, which provides an output (MIC values and S, I, or R categories). It is not an AI assistance tool for human 'readers' in the traditional sense, but rather a standalone diagnostic system.

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

Yes, a standalone performance evaluation was done. The BD Phoenix™ Automated Microbiology System is an automated system designed to provide rapid identification and antimicrobial susceptibility testing of bacterial isolates. Its performance was assessed by comparing its output (MIC and category interpretations) directly against a reference method (NCCLS broth microdilution), without human interpretation as part of the primary outcome assessment. The "algorithm only" aspect refers to the automated interpretation by the Phoenix system itself.

7. The type of ground truth used

The ground truth used was primarily the NCCLS reference broth microdilution method. For clinical isolates, results were also compared to "expected results," which are typically derived from expert consensus or established clinical practice guidelines in conjunction with reference methods. For challenge set isolates, the comparison was directly to the results from the broth microdilution method.

8. The sample size for the training set

The document does not provide specific details or sample sizes for a training set. The study described focuses on the validation of the device's performance against reference methods using a test set of clinical, stock, and challenge isolates. Automated microbiology systems often rely on established biochemical reactions and growth inhibition principles, rather than a machine learning model that requires a distinct "training set" in the common AI sense.

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

As no explicit "training set" in the machine learning context is mentioned, the method for establishing its ground truth is not described. The device's operating principles are based on established microbiological methods (redox indicator for growth detection, microdilution for MIC determination) which are inherently validated by long-standing scientific principles, rather than needing a distinct training set with its own ground truth establishment process.

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