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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 and facultative anaerobic bacteria isolates from pure culture for Enterobacteriaceae and most Gram-positive bacteria isolates from pure culture belonging to the genera Staphylococcus, Enterococcus and Streptococcus.

Ceftazidime/avibactam 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 Citrobacter freundii complex Citrobacter koseri Escherichia coli Enterobacter aerogenes Enterobacter cloacae Klebsiella pneumoniae Klebsiella oxytoca Proteus spp. Pseudomonas aeruginosa

Active In Vitro but clinical significance is unknown Morganella morganii Providencia stuartii Serratia marcescens

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. Phoenix panels are inoculated with a specified organism density and placed into the instrument. Inoculum for use with the Phoenix system may be prepared either manually or may be automated using the BD Phoenix™ AP System.

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° ± 1°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 an analysis of the provided text regarding the acceptance criteria and the study proving the device meets them:

1. A table of acceptance criteria and the reported device performance

The document references the FDA guidance document, "Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA", August 28, 2009 for the acceptance criteria. While the specific numerical thresholds for Essential Agreement (EA) and Category Agreement (CA) from this guidance aren't explicitly stated in the provided text, the reported performance is presented. Typically, for AST devices, acceptance criteria are set for these metrics.

2. Sample size used for the test set and the data provenance

• Sample Size for Test Set: 1348 isolates (This is the 'n' value reported for EA and CA).
• Data Provenance:
  • Clinical Studies: The study used "Clinical, stock and challenge isolates".
  • Geographic Origin: Tested "across multiple geographically diverse sites across the United States."
  • Retrospective or Prospective: Not explicitly stated, but the nature of a clinical study comparing to a reference method often involves prospective collection and testing or retrospective testing of collected isolates from clinical settings. The term "Clinical isolates were compared to the results obtained from the CLSI reference broth microdilution method" suggests these were real-world samples. "Challenge isolates" often refers to a pre-defined set of strains used to test specific performance aspects.

3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts

This information is not explicitly provided in the text. The ground truth for clinical isolates was established by the "CLSI reference broth microdilution method." While this is a standardized laboratory method, the number and qualifications of individuals performing these reference tests (who could be considered experts in applying the reference method) are not detailed.

4. Adjudication method for the test set

This information is not explicitly provided. The comparison is between the BD Phoenix System results and the CLSI reference broth microdilution method results. It's implied that discrepancies were evaluated to determine EA and CA, but a formal adjudication process (e.g., 2+1, 3+1 expert review in case of disagreement between tests) is not described.

5. If a multi-reader multi-case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance

This is not an MRMC study. The device is an automated antimicrobial susceptibility testing (AST) system. It performs the test and provides results (MIC values and categorical interpretations) directly, without requiring human "readers" in the same way an imaging or diagnostic AI system would. Therefore, the concept of "human readers improving with AI vs without AI assistance" does not apply here. This is an automated system being compared to a reference standard.

6. If a standalone (i.e., algorithm only without human-in-the-loop performance) was done

Yes, this is essentially a standalone (algorithm only) performance study. The BD Phoenix Automated Microbiology System is an automated device designed to determine antimicrobial susceptibility without continuous human intervention in the result interpretation once the samples are loaded. The study assesses the performance of this automated system directly against a reference method.

7. The type of ground truth used

• Clinical Isolates: The ground truth for clinical isolates was established by the CLSI reference broth microdilution method. This is a laboratory-based, standardized, and widely accepted "gold standard" method for antimicrobial susceptibility testing.
• Challenge Isolates: The ground truth for challenge isolates was compared to "expected results." This implies a pre-defined, known susceptibility profile for these specific strains, likely determined by the CLSI reference method or other validated methods.

8. The sample size for the training set

The document does not explicitly state the sample size for a training set. The descriptions focus on the validation (test) set. Automated microbiology systems like the BD Phoenix are generally developed and validated extensively over time, but the specific "training set" used for this particular antimicrobial agent's incorporation is not detailed in this regulatory summary. The system itself is "predicated" on an earlier cleared device (VITEK®2), suggesting that the base technology has been "trained" over many years/studies.

9. How the ground truth for the training set was established

As the document does not explicitly identify a "training set" for this specific clearance, it also does not describe how its ground truth was established. For the system as a whole, the ground truth would have been established through extensive comparisons to reference methods (like CLSI broth microdilution) during its initial development and subsequent updates.

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