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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 Grampositive 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 antimicrobial agent nitrofurantoin at concentrations of 8-512 ug/mL to 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.

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 breakdown of the acceptance criteria and study details for the BD Phoenix™ Automated Microbiology System for Nitrofurantoin, based on the provided document:

1. Acceptance Criteria and Reported Device Performance

The study primarily focused on demonstrating Essential Agreement (EA) and Category Agreement (CA) with a reference method. The acceptance criteria themselves are not explicitly stated with numerical thresholds in the provided text, but the reported performance serves as the basis for the FDA's substantial equivalence determination. The FDA guidance document "Guidance on Review Criteria for Assessment of Antimicrobial Susceptibility Devices", March 8, 2000, is referenced for the definition of these criteria. Generally, high percentages of EA and CA are required for clearance.

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

• Sample Size for Clinical Studies: "1646" isolates were tested (indicated by "EA (n)" and "CA (n)" in Table 1). This combines clinical, stock, and challenge isolates.
• Data Provenance: Clinical, stock, and challenge isolates were tested across "multiple geographically diverse sites across the United States." This indicates a prospective study design for the clinical and stock isolates, with challenge isolates likely being a pre-defined set.

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

The document does not specify the number of experts used or their qualifications for establishing the ground truth. The ground truth for clinical isolates was established by the NCCLS reference broth microdilution method (AST panels prepared according to NCCLS M7). For challenge isolates, the ground truth was "expected results," which would typically be determined by expert laboratories or established standards, but the specific expert involvement is not detailed.

4. Adjudication Method for the Test Set

The document does not explicitly state an adjudication method (e.g., 2+1, 3+1). The performance was compared directly to the NCCLS reference method for clinical isolates and "expected results" for challenge isolates. This implies a direct comparison rather than an expert consensus adjudication on discrepancies, though the NCCLS method itself relies on standardized procedures.

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

No Multi-Reader Multi-Case (MRMC) comparative effectiveness study was done. The study compares the automated system's performance against a reference method, not the improvement of human readers with AI assistance. The BD Phoenix System is an automated device designed to provide results directly.

6. Standalone Performance Study

Yes, a standalone performance study was done. The device, the BD Phoenix™ Automated Microbiology System, is an "algorithm only" (fully automated) system that generates MIC values and category interpretations (S, I, or R) without human intervention in the interpretation process described. Its performance was tested and compared directly to the reference method.

7. Type of Ground Truth Used

• Clinical Isolates: The ground truth was established using the NCCLS reference broth microdilution method (AST panels prepared according to NCCLS M7). This is a standardized laboratory reference method.
• Challenge Isolates: The ground truth was "expected results," which are typically predetermined values for known strains.

8. Sample Size for the Training Set

The document does not specify the sample size for any training set. As this is a 510(k) submission for a specific antimicrobial and organisms for an existing automated system (BD Phoenix), the development and initial training of the core algorithm would have occurred prior to this specific submission. This document focuses on the validation of the system for a new antimicrobial agent.

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

As the training set sample size is not specified, the method for establishing its ground truth is also not described in this document. However, given the nature of the device, it would have likely involved similar reference methods (like NCCLS broth microdilution) and phenotypic characterization for organism identification and AST during the initial development and training of the BD Phoenix System's algorithms.

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