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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 removal of limitations for Enterobacter cloacae and Serratia species from the original premarket notification [K023895, 1/8/2003] for the antimicrobial agent ciprofloxacin at concentrations of 0.25-4 ug/ml to Gram-negative ID/AST or AST only Phoenix panels. The concentration range has been reduced by one dilution from the range of 0.125-4ug/ml in the original 510(k). Ciprofloxacin has been shown to be active in vitro against most strains of microorganisms listed below, as described in the FDA-approved package insert for this antimicrobial agent.

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 containing biochemicals 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 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 as well as bacterial turbidity are used in the determination of bacterial growth. Each AST panel configuration 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°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).

Here's a summary of the acceptance criteria and study details for the BD Phoenix™ Automated Microbiology System's Ciprofloxacin 0.25-4 µg/ml update, based on the provided text:

Acceptance Criteria and Reported Device Performance

Note: The exact numerical acceptance criteria for EA and CA are not explicitly stated in the provided text. However, medical device submissions for antimicrobial susceptibility systems typically aim for values well above 90% for both essential and category agreement when compared to a reference method, as indicated by the reference to "substantial equivalence" and FDA guidance. The reported performance of 90.6% EA and 97.4% CA suggests these values met the internal and regulatory acceptance thresholds. The reproducibility criteria are explicitly stated and met.

Study Details

1. Sample size used for the test set and the data provenance:

   • Test Set Sample Size: Not explicitly stated as a single number. The study involved "clinical, stock and challenge isolates."
   • Data Provenance: Multiple geographically diverse sites across the United States. Retrospective and prospective status is not explicitly stated, but clinical isolates typically refer to prospectively collected samples from patients, while stock and challenge isolates are curated for specific testing purposes.

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

   • This information is not provided in the document. The ground truth for clinical isolates was established by the CLSI reference broth microdilution method, which is a standardized laboratory procedure, not typically relying on expert interpretation in the same way as, for example, image analysis. For challenge isolates, the "expected results" served as the ground truth, implying pre-determined results for these strains.

3. Adjudication method for the test set:

   • Not applicable in the traditional sense. The comparison was against the CLSI reference broth microdilution method or "expected results" for challenge isolates. Discrepancies would be analyzed according to the definitions of Essential Agreement (within +/- one two-fold dilution) and Category Agreement (matching FDA categorical interpretive criteria). This is a direct comparison to a gold standard method, not an adjudication among human readers.

4. 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. This is an automated microbiology system that performs antimicrobial susceptibility testing (AST). It is not an AI system designed to assist human readers in interpretation. The output is already an interpretation (MIC values, S/I/R categories).

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

   • Yes, this was a standalone performance evaluation of the BD Phoenix™ Automated Microbiology System. The device automatically reads and interprets the results to provide MIC values and categorical interpretations (S, I, R). Human intervention is limited to preparing the inoculum and loading the panels.

6. The type of ground truth used:

   • For clinical isolates: CLSI (Clinical and Laboratory Standards Institute) reference broth microdilution method. This is a recognized gold standard laboratory method for antimicrobial susceptibility testing.
   • For challenge isolates: "Expected results," implying pre-established, known susceptibility profiles for these specific strains.

7. The sample size for the training set:

   • This information is not provided. The document describes a "device" (BD Phoenix Automated Microbiology System), not an AI algorithm that would typically have a distinct training set. The system's "training" or development would have been part of its initial design and validation, prior to this specific antimicrobial agent's clearance, and involved developing its underlying algorithms for growth detection and MIC determination.

8. How the ground truth for the training set was established:

   • This information is not provided because a distinct "training set" for an AI algorithm is not explicitly mentioned or applicable in the context of this device's submission. The system's foundational algorithms would have been developed and validated against established microbiological methods, similar to how the test set's ground truth was established, but over a much broader range of organisms and antimicrobials during the initial design and development phases.

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