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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 the antimicrobial susceptibility of isolates (minimum inhibitory concentration (MIC)) of most Gram-negative aerobic and facultative anaerobic bacteria isolates from pure culture for Enterobacteriaceae and Non-Enterobacteriaceae and Gram-positive aerobic and facultative anaerobic bacteria isolates from pure culture belonging to the genera Staphylococcus, Enterococcus and Streptococcus.

This premarket notification is for the addition of the antimicrobial agent levofloxacin at concentrations of 0.25-16 ug/mL to Streptococcus ID/AST or AST only Phoenix Panels. Levofloxacin has been shown to be active in vitro and in clinical infections against Streptococcus pneumoniae (including penicillin-resistant strains) and Streptococcus pyogenes. Levofloxacin has been shown to be active in vitro against Streptococcus (Group C), Streptococcus (Group G), Streptococcus agalactiae, and Streptococcus viridans group (Viridans group streptococci, Streptococcus (Group F), and Streptococcus milleri).

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. For testing streptococcal species the system includes the following components:

• BD Phoenix instrument and software.
• BD 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-S Broth used for performing AST tests only.
• BD Phoenix AST-S 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, R or N (susceptible, intermediate, resistant or nonsusceptible).

Here's a breakdown of the acceptance criteria and study information for the BD Phoenix™ Automated Microbiology System - Levofloxacin 0.25-16 µg/mL, based on the provided 510(k) summary:

Acceptance Criteria and Device Performance

Study Details

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

• Test Set Sample Size: 1055 isolates were tested for Levofloxacin. This includes "Clinical, stock and challenge isolates."
• Data Provenance: The isolates were tested "across multiple geographically diverse sites across the United States." The study used a combination of:
  • Clinical isolates: Compared to the CLSI reference broth microdilution method.
  • Stock isolates: Likely reference strains from culture collections.
  • Challenge isolates: Compared to expected results.
    The study is therefore prospective in nature, as it involves testing isolates on the device and comparing them to a reference method, rather than analyzing pre-existing data.

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 or qualifications of experts involved in establishing the ground truth.
• The ground truth for clinical isolates was established by the CLSI reference broth microdilution method.
• The ground truth for challenge isolates was established by "expected results," implying pre-determined characteristics.

4. Adjudication method for the test set:

• The document does not explicitly describe an adjudication method involving multiple experts for the test set results.
• The comparison is primarily a direct comparison of the Phoenix System results to either the CLSI reference method or expected results for challenge isolates.

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. This is an automated microbiology system for antimicrobial susceptibility testing. The effectiveness study performed is a comparison of the automated device's performance against a reference laboratory method, not an assessment of human readers with or without AI assistance. Therefore, an MRMC study and effect size for human readers are not applicable.

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

• Yes. The study evaluates the "BD Phoenix™ Automated Microbiology System" as a standalone device. Its performance (MIC values and category interpretations) is directly compared to a reference method without human interpretation of the device's raw output. The system is designed to provide automated results.

7. The type of ground truth used:

• Expert Consensus / Reference Method: For clinical isolates, the ground truth was established by the CLSI reference broth microdilution method, which is a standardized, expert-defined method.
• Expected Results: For challenge isolates, the ground truth was "expected results," meaning pre-defined and verified characteristics of the strains.

8. The sample size for the training set:

• The document does not explicitly state the sample size for a training set. This is typical for a microbiology susceptibility test where the "training" usually involves establishing the parameters and algorithms based on extensive prior knowledge of microbial growth and drug interaction, rather than an explicit machine learning training set in the contemporary sense. The system's underlying algorithms are likely developed and validated using a large body of historical data and microbiological principles, which are not detailed as a "training set" in this type of submission.

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

• As a specific "training set" is not detailed, the establishment of ground truth for any underlying algorithm development would have been based on established microbiological principles, reference methods (like CLSI microbroth dilution), and extensive empirical data collected over time during the development of the Phoenix system. This involves correlating phenotypic growth responses to known antimicrobial concentrations and clinical outcomes. This information is not explicitly provided in the 510(k) summary for a "training set."

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