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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 cetriaxone at concentrations of 0.5-64 ug/mL to Gram-negative ID/AST or AST only Phoenix panels. cetriaxone 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.

Active In Vitro and in Clinical Infections Against:

Acinetobacter calcoaceticus Enterobacter aerogenes Enterobacter cloacae Escherichia coli

Klebsiella oxytoca Klebsiella pneumoniae Morganella morganii Proteus mirabilis

Serratia marcescens Pseudomonas aeruginosa

Active In Vitro Against:

Citrobacter koseri (formerly C. diversus) Citrobacter freundii Providencia species (including Providencia rettgeri) Salmonella species Shigella species

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 isolation 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 breakdown of the acceptance criteria and study details based on the provided text:

1. Table of Acceptance Criteria and Reported Device Performance

The acceptance criteria are not explicitly stated as distinct numerical targets but are implied through the comparison with the NCCLS reference method and the FDA's guidance document for "Essential Agreement" (EA) and "Category Agreement" (CA). The study demonstrates the device meets the implied criteria by achieving high agreement percentages.

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

• Sample Size for Test Set:
  • Clinical Studies (Clinical, Stock, and Challenge Isolates): 1791 isolates for which EA and CA are reported for Ceftriaxone.
  • Site Reproducibility (Gram-negative isolates): Not explicitly stated, but "a panel of Gram-negative isolates" was tested, with each site testing isolates in triplicate on three different days.
• Data Provenance: Clinical, stock, and challenge isolates were tested across multiple geographically diverse sites across the United States. This indicates prospective data collection from multiple sites within the United States.

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

This information is not explicitly provided in the document. The document states that the ground truth for clinical isolates was established by comparing Phoenix System results to the NCCLS reference broth microdilution method. For challenge isolates, results were compared to "expected results." The document does not detail how these "expected results" were derived or whether expert adjudication was involved in establishing the NCCLS reference method results or the expected results for challenge isolates in this specific study.

4. Adjudication Method for the Test Set

The document does not explicitly describe an adjudication method involving expert review for the test set. The primary comparison for clinical isolates was against the NCCLS reference broth microdilution method. For challenge isolates, it was against "expected results." This suggests a direct comparison to a reference standard rather than an adjudication process between human readers.

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 is an automated system for determining antimicrobial susceptibility (MIC values and category interpretations) directly, not an AI-assisted tool for human readers. Therefore, the concept of improving human readers with vs. without AI assistance does not apply here.

6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) Was Done

Yes, a standalone performance study was done. The BD Phoenix Automated Microbiology System is itself an automated system ("algorithm only") that determines antimicrobial susceptibility without human interpretation in the results generation phase. The study directly assesses the performance of this automated system against a reference method.

7. The Type of Ground Truth Used

• Clinical Isolates: The ground truth was established by the NCCLS reference broth microdilution method. This is a laboratory-based, standardized, and validated method for determining antimicrobial susceptibility.
• Challenge Isolates: The ground truth was based on "expected results." The document does not detail how these "expected results" were defined, but they typically refer to results from well-characterized strains where susceptibility is known.

8. The Sample Size for the Training Set

The document does not specify a sample size for a training set. As an automated microbiology system that assesses growth and inhibition, it's more likely that the system's underlying algorithms (e.g., for interpreting redox indicator changes and bacterial turbidity) were developed and validated using extensive physiological and microbiological data, rather than a specific "training set" in the machine learning sense described here. The study focuses on the validation of the device's performance with a new antimicrobial agent.

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

Since a specific "training set" in the context of machine learning is not mentioned, the method for establishing its ground truth is also not described. The device's operation is based on established microbiological principles (broth microdilution, redox indicators, turbidity measurement), rather than being a purely AI-driven predictive model that requires a labeled training set in the typical sense.

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