(114 days)
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 Gram-positive aerobic and facultative anaerobic bacteria isolates from pure culture belonging to the genera Staphylococcus and Enterococcus.
This premarket notification is for the addition of the antimicrobial agent trimethoprim-sulfamethoxazole at concentrations of 0.5/9.5 - 16/304 ug/mL to Gram Positive ID/AST or AST only Phoenix panels.
The BD Phoenix Automated Microbiology System (Phoenix System) is an automated system for the 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 consumable supplies and reagents 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, R or N (susceptible, intermediate, resistant or not susceptible).
Here's a breakdown of the acceptance criteria and the study details for the BD Phoenix™ Automated Microbiology System – Trimethoprim-sulfamethoxazole (0.5/9.5 - 16/304 µg/mL), based on the provided 510(k) summary:
1. Table of Acceptance Criteria and Reported Device Performance
The acceptance criteria for antimicrobial susceptibility devices are typically based on Essential Agreement (EA) and Category Agreement (CA) when compared to a recognized reference method (in this case, the NCCLS reference broth microdilution method). While numerical thresholds for acceptance criteria (e.g., "EA must be >90%") are often implied or stated in guidance documents, they are not explicitly presented as a hard table of acceptance criteria in this summary. However, the study aims to demonstrate "substantially equivalent performance," which implies meeting common industry and regulatory expectations for these metrics.
| Metric | Implied Acceptance Criteria (typical for AST devices, not explicitly stated numerically as AC in text but implied by "substantially equivalent") | Reported Device Performance |
|---|---|---|
| Essential Agreement (EA) | High percentage (e.g., often >90% or >95% for AST devices) | 96.4% |
| Category Agreement (CA) | High percentage (e.g., often >90% or >95% for AST devices) | 97.9% |
| Intra-site Reproducibility | >90% | >90% |
| Inter-site Reproducibility | >95% | >95% |
Definitions from the text:
- Essential Agreement (EA): Occurs when the BD Phoenix™ Automated Microbiology System agrees exactly or within ± one doubling dilution to the reference result (MIC).
- Category Agreement (CA): Occurs when the BD Phoenix™ Automated Microbiology System agrees with the reference method with respect to the FDA categorical interpretive criteria (susceptible, intermediate, resistant or not susceptible).
2. Sample Size Used for the Test Set and Data Provenance
- Test Set Sample Size: The "n" value reported for Essential Agreement (EA) and Category Agreement (CA) for Trimethoprim-sulfamethoxazole is 634. This represents the total number of isolates tested for this specific antimicrobial agent.
- Data Provenance: The study was conducted across "multiple geographically diverse sites across the United States." This indicates the data is prospective in nature, as it was specifically collected for this performance validation.
3. Number of Experts Used to Establish Ground Truth for the Test Set and Their Qualifications
The document does not explicitly state the number of experts or their specific qualifications (e.g., "radiologist with 10 years of experience") used to establish the ground truth. The ground truth (reference method) was the NCCLS reference broth microdilution method, which is a standardized laboratory technique. While skilled microbiologists would perform this reference method, the document does not detail specific "experts" in the sense of clinical reviewers adjudicating individual cases.
4. Adjudication Method for the Test Set
There is no mention of an adjudication method like "2+1" or "3+1" because the ground truth was established by the NCCLS reference broth microdilution method, which is a laboratory assay. This method inherently produces a definitive result (MIC and categorical interpretation) based on established protocols, rather than requiring expert consensus or adjudication of subjective interpretations.
5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study
- No, an MRMC comparative effectiveness study was not done. This type of study is more common for imaging devices where human readers interpret results, and the AI's role is to assist human interpretation.
- The Phoenix System is an automated device designed to replace manual susceptibility testing or provide results quickly, not to assist human readers in interpreting an image or complex finding. Therefore, the effect size of human readers improving with AI vs. without AI assistance is not applicable here.
6. Standalone (Algorithm Only Without Human-in-the-Loop Performance) Study
- Yes, a standalone study was performed. The study directly compares the performance of the BD Phoenix™ Automated Microbiology System's automated results (algorithm only) against the NCCLS reference method. There is no mention of human intervention or interpretation of the Phoenix system's outcome; the system directly provides the MIC and category interpretation.
7. Type of Ground Truth Used
The primary ground truth used for performance comparison was the NCCLS reference broth microdilution method. This is a recognized and standardized laboratory method for determining antimicrobial minimum inhibitory concentrations (MICs) and corresponding categorical interpretations (Susceptible, Intermediate, Resistant). For "Challenge set isolates," the Phoenix System results were compared to "expected results," which presumably refers to established values for known strains.
8. Sample Size for the Training Set
The document does not provide information regarding the sample size used for the training set. This is common for older 510(k) summaries, especially for devices where the underlying technology (e.g., redox indicator for growth detection) relies more on established biophysical principles and empirically derived thresholds than on machine learning models requiring large labeled training datasets.
9. How the Ground Truth for the Training Set Was Established
Since the document does not mention a training set or its size, it also does not specify how the ground truth for any potential training set was established. It's plausible that the system's underlying logic and thresholds were developed through extensive R&D and validation against reference methods, but a formal "training set" in the modern AI/ML sense is not detailed.
§ 866.1645 Fully automated short-term incubation cycle antimicrobial susceptibility system.
(a)
Identification. A fully automated short-term incubation cycle antimicrobial susceptibility system is a device that incorporates concentrations of antimicrobial agents into a system for the purpose of determining in vitro susceptibility of bacterial pathogens isolated from clinical specimens. Test results obtained from short-term (less than 16 hours) incubation are used to determine the antimicrobial agent of choice to treat bacterial diseases.(b)
Classification. Class II (special controls). The special control for this device is FDA's guidance document entitled “Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA.”