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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 antilitive 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 the addition of the antimicrobial agent linezolid at concentrations of 0.25-16 ug/mL to Streptococcus ID/AST or AST only Phoenix panels. Linezolid 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:

Streptococcus agalactiae Streptococcus pneumoniae (penicillin-susceptible strains only) Streptococcus pyogenes

Active In Vitro Against:

Streptococcus pneumoniae (penicillin-resistant strains) Viridans group streptococci

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 Streptococcus 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 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, R or N (susceptible, intermediate, resistant or not susceptible).

Here's a breakdown of the acceptance criteria and study details for the BD Phoenix™ Automated Microbiology System for Linezolid, based on the provided text:

Acceptance Criteria and Device Performance

The acceptance criteria for the BD Phoenix™ Automated Microbiology System when testing Linezolid in streptococcal organisms are based on Essential Agreement (EA) and Category Agreement (CA) with a CLSI reference broth microdilution method.

Note: While specific numerical acceptance criteria for EA and CA are not explicitly given in the provided text, the conclusion of "substantially equivalent performance" implicitly indicates that these reported percentages met the pre-defined acceptance thresholds as per the FDA guidance document.

Study Details

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

• Test Set Sample Size: The exact number of individual isolates in the "test set" (clinical, stock, and challenge isolates combined) is not directly stated as a single number. However, the performance metrics provide counts:
  • Essential Agreement (EA) was calculated from n = 1071 results.
  • Category Agreement (CA) was calculated from n = 1907 results.
• Data Provenance: The study used a mix of:
  • Clinical isolates: These are typically prospective, collected from patient samples.
  • Stock isolates: (Strain collections) could be either retrospective or prospective, depending on how they were obtained.
  • Challenge isolates: These are typically curated strains used to challenge the system's performance, often not from recent patient samples.
• Country of Origin: "across multiple geographically diverse sites across the United States."

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

• Number of Experts: Not specified.
• Qualifications of Experts: Not specified. The ground truth for the test set was established by the CLSI reference broth microdilution method (for clinical isolates) and "expected results" for challenge isolates, rather than individual expert interpretation of the device output. This implies that the 'experts' would be the laboratory personnel performing and interpreting the reference method.

4. Adjudication Method for the Test Set

• Adjudication Method: Not applicable in the traditional sense of resolving discrepancies between human readers. The comparative method was between the automated device and a standardized reference laboratory method (CLSI broth microdilution). Discrepancies between the Phoenix System and the reference method were quantified as lack of essential or category agreement, not adjudicated by a third party.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done, and Effect Size

• MRMC Study: No, an MRMC comparative effectiveness study was not explicitly done in the context of comparing human readers with and without AI assistance. This study focuses on the standalone performance of an automated system against a reference method.

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

• Standalone Performance: Yes, the study primarily assessed the standalone performance of the BD Phoenix™ Automated Microbiology System. The device itself automatically interprets the results to give MIC values and categorical interpretations (S, I, R, or N) without direct human intervention in the interpretation process of each reading. Human involvement is in setting up the test and reviewing the final results.

7. The Type of Ground Truth Used

• Ground Truth Type:
  • Reference Method: For clinical isolates, the ground truth was "results obtained from the CLSI reference broth microdilution method." CLSI (Clinical and Laboratory Standards Institute) methods are widely accepted laboratory standards for antimicrobial susceptibility testing.
  • "Expected Results": For challenge isolates, the ground truth was "expected results." These expected results are typically established through robust prior testing using gold-standard methods or expert consensus on known strains.

8. The Sample Size for the Training Set

• Training Set Sample Size: Not explicitly mentioned in the provided text. The text describes a "test set" and studies for validation, but does not detail the specific training dataset used to develop the Phoenix System's algorithms.

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

• Training Set Ground Truth Establishment: Not explicitly mentioned or detailed in the provided text. Typically, ground truth for training AST systems would involve a large collection of isolates tested by a recognized reference method (like CLSI broth microdilution) with expert confirmation, similar to how the ground truth for the test set was established.

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