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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-Enteriaceae and most Gram-positive bacteria isolates from pure culture belonging to the genera Staphylococcus, Enterococcus, and Streptococcus.

This premarket notification is for the addition of the antimicrobial agent cefoxitin at concentrations of 0.5-64 ug/mL to gram-negative ID/AST or AST only Phoenix panels. Cefoxitin 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 spp. (including K. pneumoniae) Morganella morqanii

Proteus mirabilis Proteus vulgaris Providencia spp. (including P. rettgeri)

Active In Vitro Against:

Klebsiella oxytoca

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 t 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 an analysis of the provided text regarding the acceptance criteria and study for the BD Phoenix™ Automated Microbiology System - Cefoxitin – 0.5-64 µg/mL.

Acceptance Criteria and Device Performance Study

The study evaluates the performance of the BD Phoenix™ Automated Microbiology System for antimicrobial susceptibility testing of Cefoxitin against specific Gram-negative bacteria. The performance is assessed by comparing its results to a CLSI reference broth microdilution method.

1. Table of Acceptance Criteria and Reported Device Performance

The acceptance criteria are implied by the "Essential Agreement (EA)" and "Category Agreement (CA)" metrics, which are standard for AST systems. While the document states that the system met these criteria (demonstrated "substantially equivalent performance"), the actual numerical acceptance limits for EA and CA are not explicitly defined in the provided text. However, typical FDA guidance for AST devices requires high percentage agreement. The table below presents the reported performance based on the general statements.

Note on Table 1: The content of "Table 1" in the provided text is highly corrupted and unreadable. Therefore, specific numerical performance metrics for EA and CA cannot be extracted directly from it. The description focuses on the definition of EA and CA and the overall conclusion of substantial equivalence.

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

• Sample Size for Test Set: The document mentions "clinical, stock and challenge isolates" were tested. While it states "Table 1 summarizes the performance for the isolates tested in this study," the corrupted nature of Table 1 prevents extraction of the exact number of isolates for the Cefoxitin-specific study. However, for a 510(k) submission for AST, this would typically involve hundreds to thousands of isolates across various species.
• Data Provenance: The isolates were tested "across multiple geographically diverse sites across the United States." This indicates a prospective collection or a mix of prospective (clinical) and well-characterized retrospective (stock/challenge) isolates. The "clinical isolates" would be prospectively collected from patient samples, while "stock and challenge isolates" are typically well-characterized laboratory strains used for specific testing purposes.

3. Number of Experts and Qualifications for Ground Truth

The document does not explicitly state the number or qualifications of experts used to establish the ground truth. However, the ground truth for antimicrobial susceptibility testing is established by the "CLSI reference broth microdilution method," which is a highly standardized laboratory procedure. This method is performed by trained laboratorians according to rigorous protocols, rather than relying on subjective expert interpretation like in image-based diagnostics. The "experts" in this context are the trained laboratory personnel performing the reference method.

4. Adjudication Method for the Test Set

There is no mention of an adjudication method in the context of expert review. This is expected because the ground truth for AST is determined by a standardized reference laboratory method (CLSI broth microdilution), which yields an objective result (MIC value and categorical interpretation). Discrepancies between the device and the reference method are analyzed for agreement, not adjudicated by a panel of human experts.

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

No Multi-Reader Multi-Case (MRMC) comparative effectiveness study was done. This type of study is typically performed for diagnostic devices where human interpretation of results is involved (e.g., radiology, pathology). The BD Phoenix™ System is an automated system for objective measurement of microbial growth inhibition, and its "effectiveness" is compared against a gold standard method (CLSI reference) rather than against human readers' performance with or without AI assistance.

6. Standalone Performance Study (Algorithm only without human-in-the-loop performance)

Yes, a standalone performance study was done. The entire study described is a standalone performance evaluation of the BD Phoenix™ Automated Microbiology System. The device directly provides Minimum Inhibitory Concentration (MIC) values and categorical interpretations (S, I, R) without human intervention in the primary interpretation loop. The Phoenix System's results are then compared to the CLSI reference method.

7. Type of Ground Truth Used

The ground truth used is the CLSI reference broth microdilution method. This is a highly standardized and accepted laboratory method for determining antimicrobial susceptibility, widely considered the "gold standard" for this type of testing. For challenge isolates, "expected results" were used, which are also derived from established reference methods and historical characterization.

8. Sample Size for the Training Set

The document does not provide information about a separate "training set" or its sample size. Antomicrobial Susceptibility Testing (AST) systems like the BD Phoenix are developed and validated using a different paradigm than typical AI/ML algorithms that require explicit training sets. The development typically involves:

• Algorithm development: Based on principles of microbiology, redox indicators, and bacterial growth kinetics.
• Calibration: Using a diverse set of characterized isolates to calibrate the system's readings and interpretation rules against the reference method. This is more akin to a calibration/optimization set than a traditional ML "training set."

The isolates mentioned (clinical, stock, challenge) are part of the performance evaluation or test set that demonstrates the device's accuracy against the reference method, not a separate training set for an AI/ML model.

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

As noted above, a traditional "training set" for an AI/ML model is not explicitly mentioned or implied for this device's validation. If any internal calibration or optimization involved a set of isolates, their ground truth would have been established using the CLSI reference broth microdilution method, consistent with the test set's ground truth. However, the document provided focuses solely on the performance evaluation against the reference standard for regulatory submission.

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