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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, Enterococcus, and Streptococcus.

This premarket notification is for additional organism groups and BD Phoenix™ Automated Microbiology System with Nitrofurantoin (8-512 ug/mL), Trimethoprim-sulfamethoxazole (0.5/9.5-16/304 µg/ mL) and Nalidixic Acid (2-32µg/mL) on Gram-negative ID/AST or AST only Phoenix panels.

Nitrofurantoin 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:

Escherichia coli

Active In Vitro Against:

Citrobacter amalonaticus
Citrobacter koseri (diversus)
Citrobacter freundii
Klebsiella oxytoca
Klebsiella pneumoniae (ozaenae)

Trimethoprim-sulfamethoxazole 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:

Escherichia coli
Klebsiella species
Enterobacter species
Morganella morganii
Proteus mirabilis
Proteus vulgaris
Shigella flexneri
Shigella sonnei

Nalidixic Acid 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:

Enterobacter species
Escherichia coli
Morganella morganii
Proteus mirabilis
Proteus vulgaris
Providencia rettgeri

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 t 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 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 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. Phoenix panels are inoculated with a specified organism density and placed into the instrument.

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).

The provided document describes the performance of the BD Phoenix™ Automated Microbiology System for antimicrobial susceptibility testing (AST) of Nitrofurantoin, Trimethoprim-sulfamethoxazole, and Nalidixic Acid against certain bacterial isolates.

Here's the breakdown of the acceptance criteria and study details:

1. Table of Acceptance Criteria and Reported Device Performance:

The document implicitly refers to the FDA Draft Guidance Document, "Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA," February 5, 2003, for defining acceptance criteria. While explicit numerical acceptance thresholds (e.g., "EA must be > 90%") are not stated in the provided text, the study's aim was to demonstrate "substantially equivalent performance" to the CLSI reference method as outlined in this guidance. The performance metrics reported are Essential Agreement (EA) and Category Agreement (CA).

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

• Sample Size for Test Set:
  • Nitrofurantoin: 2130 isolates
  • Trimethoprim-sulfamethoxazole: 2212 isolates
  • Nalidixic Acid: 2103 isolates
• Data Provenance: Clinical, stock, and challenge isolates were tested. The clinical isolates were collected from "multiple geographically diverse sites across the United States." The study also included "challenge isolates" to compare against expected results, implying a controlled set of strains with known characteristics. The study is prospective in the sense that the testing was performed specifically for this submission, although the source of the clinical isolates themselves could be retrospective collections.

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

The document does not specify the number of experts or their qualifications for establishing ground truth. The ground truth for clinical isolates was established by the CLSI reference broth microdilution method. For challenge isolates, it was compared to "expected results," which would be based on predefined characteristics of those strains.

4. Adjudication Method for the Test Set:

Not applicable. This type of study (Antimicrobial Susceptibility Testing) does not typically involve human adjudication of results in the way, for example, a radiology AI study might. The "ground truth" is determined by a standardized laboratory reference method (CLSI broth microdilution).

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done, and the Effect Size of How Much Human Readers Improve with AI vs. Without AI Assistance:

This type of study was not performed. The BD Phoenix™ Automated Microbiology System is an automated device designed to perform AST, not to assist human readers in interpreting images or other complex data. It provides interpreted results directly (MIC values and S/I/R categories).

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

Yes, a standalone performance study was conducted. The "BD Phoenix™ Automated Microbiology System" is the device being evaluated, and its results (MIC and S/I/R interpretations) are directly compared to the reference method. There is no human intervention mentioned as part of the system's performance assessment or result generation.

7. The Type of Ground Truth Used:

The ground truth used was:

• For clinical isolates: CLSI reference broth microdilution method (a laboratory reference standard).
• For challenge isolates: Expected results, which implies a predefined standard for these specific strains.

8. The Sample Size for the Training Set:

The document does not provide information regarding a separate training set. The descriptions focus on the validation (clinical evaluation) of the device. It's common for such commercial systems, especially those that have predicate devices, to leverage extensive prior development data and methodologies rather than detail a single "training set" for a new submission of additional antimicrobial agent/organism combinations.

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

As no training set is explicitly described, the method for establishing its ground truth is not provided.

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