(83 days)
ETEST® is a manual, quantitative technique for the determination of antimicrobial susceptibility of non‑fastidious Gram‑negative and Gram‑positive aerobic bacteria and fastidious bacteria. The system comprises a predefined antibiotic gradient which is used to determine the Minimum Inhibitory Concentration (MIC, in μg/mL) of different antimicrobial agents against microorganisms tested on agar media after overnight incubation.
Testing with ETEST® Aztreonam/Avibactam (AZA) (0.016/4-256/4 μg/mL) is indicated for Enterobacterales, as recognized by the FDA Susceptibility Test Interpretive Criteria (STIC).
The ETEST® Aztreonam/Avibactam (AZA) (0.016/4-256/4 μg/mL) demonstrated acceptable performance with the following microorganisms:
• Enterobacterales:
- Escherichia coli
- Klebsiella pneumoniae
- Klebsiella aerogenes
- Citrobacter freundii complex
- Citrobacter koseri
- Enterobacter cloacae complex
- Proteus mirabilis
- Proteus vulgaris
- Morganella morganii
- Providencia stuartii
- Serratia marcescens
ETEST® is a thin, inert and non-porous plastic strip carrying the MIC reading scale in μg/mL on one side and a predefined antibiotic gradient on the other side.
When the strip is applied to an inoculated agar surface, the preformed antibiotic gradient immediately transfers into the agar matrix, then forming a stable, continuous and exponential gradient of antibiotic concentrations directly underneath the strip. Bacterial growth becomes visible during incubation, and a symmetrical inhibition ellipse centered along the strip appears. The MIC value is read from the scale in terms of μg/mL at complete inhibition of bacterial growth, where the pointed end of the ellipse intersects the strip.
ETEST® Aztreonam/Avibactam (AZA) (0.016/4-256/4 µg/mL) contains a range of Aztreonam from (0.016-256 µg/mL), overlaid with a fixed concentration of 4 µg/mL of Avibactam.
The provided FDA 510(k) clearance letter describes the acceptance criteria and the study proving the ETEST Aztreonam/Avibactam (AZA) device meets these criteria for determining antimicrobial susceptibility.
Here's a breakdown of the requested information:
1. Table of Acceptance Criteria and Reported Device Performance
The acceptance criteria for antimicrobial susceptibility test (AST) systems, as outlined by the FDA and CLSI (Clinical and Laboratory Standards Institute), are primarily based on Essential Agreement (EA) and Category Agreement (CA) with a reference method.
The acceptance criteria are implicitly met if the reported performance metrics achieve or exceed the established thresholds (though the exact numerical acceptance thresholds for EA and CA are not explicitly stated as "acceptance criteria" values in this document, standard FDA guidance for AST devices typically requires EA ≥ 90% and CA ≥ 90% for overall performance).
| Performance Metric | Acceptance Criteria (Implicit, based on typical FDA AST guidance) | Reported Device Performance (ETEST Aztreonam/Avibactam) |
|---|---|---|
| Essential Agreement (EA) (overall species) | ≥ 90% (typical guidance) | 95.7% (within ± 1 dilution of the reference method) |
| Category Agreement (CA) (overall species) | ≥ 90% (typical guidance) | 98.0% |
| Reproducibility | Acceptable (e.g., ≥ 95% within defined range) | Best case = 100%, Worst case = 98.5% |
| Quality Control | > 95% within expected QC results range | > 95% within the expected QC results range |
Note: The document also states that the device "demonstrated substantially equivalent performance when compared with the CLSI M07-11th Ed (January 2018) broth microdilution reference method, following rules as defined in the FDA Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA, issued on August 28, 2009 and following specifications as defined in CLSI M100 35th Ed. (January 2025)." This indicates adherence to established regulatory and standard-setting body guidelines for performance.
2. Sample Size Used for the Test Set and Data Provenance
- Sample Size for Test Set: A total of 602 strains of Enterobacterales were used for the performance evaluation.
- This included:
- Escherichia coli (150 strains)
- Klebsiella pneumoniae (118 strains)
- Enterobacter cloacae complex (67 strains, including E. cloacae, E. hormaechei, E. asburiae, E. roggenkampii, E. ludwigii)
- Citrobacter freundii complex (50 strains, including C. freundii, C. braakii, C. murliniae, C. portucalensis)
- Citrobacter koseri (30 strains)
- Klebsiella aerogenes (32 strains)
- Morganella morganii (30 strains)
- Proteus mirabilis (32 strains)
- Providencia stuartii (30 strains)
- Proteus vulgaris (30 strains)
- Serratia marcescens (33 strains)
- Additionally, 12 Enterobacterales resistant isolates with high MIC values (≥ 16 µg/mL) were specifically included: Klebsiella pneumoniae (2), Escherichia coli (8), Serratia marcescens (1) and Enterobacter cloacae complex (1).
- This included:
- Data Provenance: The document states "External evaluations were conducted with fresh and stock clinical isolates, as well as a set of challenge strains." This implies a mix of retrospective (stock clinical isolates, challenge strains) and prospective (fresh clinical isolates) data. The country of origin of the data is not specified in this document.
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications
This document describes the validation of an in vitro diagnostic device for antimicrobial susceptibility testing, not an imaging AI device requiring expert human reads. Therefore, the concept of "experts" to establish ground truth in the context of human readers is not directly applicable.
Instead, the ground truth was established by a reference method: the CLSI (Clinical and Laboratory Standards Institute) M07-11th Ed (January 2018) broth microdilution reference method. This method is considered the gold standard for determining Minimum Inhibitory Concentrations (MICs) in microbiology. The qualifications of personnel performing this reference method would be standard microbiology laboratory technicians or scientists trained in CLSI methods, rather than clinical experts like radiologists. The number of individuals/laboratories involved in performing the reference method is not specified.
4. Adjudication Method for the Test Set
Not applicable in the context of in vitro diagnostic device validation using a reference laboratory method. Adjudication methods (like 2+1 or 3+1) are typically used in clinical studies where human readers provide subjective interpretations, and conflicts need resolution. Here, the ground truth is a quantitative, standardized microbiology assay.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done, and Effect Size of Human Improvement with AI Assistance
Not applicable. This is an in vitro diagnostic device (a test strip) for determining antimicrobial susceptibility, not an AI-assisted diagnostic tool for human image interpretation. Therefore, no MRMC study or assessment of human reader improvement with AI assistance was conducted.
6. If a Standalone (Algorithm Only Without Human-in-the-Loop Performance) Was Done
The device itself is a manual, quantitative technique. It is a physical strip that produces a visual inhibition zone from which a Bacterial MIC value is read. It does not involve a software algorithm in the way an AI diagnostic tool would. Therefore, the concept of "standalone performance" of an "algorithm" is not directly applicable in the same sense as for an AI product.
The performance evaluation (which can be considered analogous to "standalone performance" in that it assesses the device's accuracy without a human "interpretation" component beyond reading the scale) was done by comparing the ETEST Aztreonam/Avibactam (AZA) strip's results to the CLSI broth microdilution reference method. This demonstrates the device's inherent capability to accurately determine MIC values.
7. The Type of Ground Truth Used
The ground truth used was the CLSI M07-11th Ed (January 2018) broth microdilution reference method. This is a highly standardized and accepted laboratory reference method for determining the Minimum Inhibitory Concentration (MIC) of an antimicrobial agent against a microorganism. It serves as the definitive 'truth' against which the performance of the ETEST device is measured.
8. The Sample Size for the Training Set
The document does not explicitly mention a "training set" in the context of machine learning model development. This is an in vitro diagnostic device, not a software algorithm that undergoes a distinct training phase. The development of such devices typically involves extensive R&D, formulation optimization, and internal testing before external clinical evaluations. The "training" in this context would refer to the development and optimization of the test strip's chemical gradient to accurately reflect MIC values, rather than training a data-driven model. The document focuses on the validation (test set) for regulatory clearance.
9. How the Ground Truth for the Training Set Was Established
As noted above, the concept of a "training set" and associated ground truth establishment methods for it, as typically applied to machine learning, is not directly relevant to this type of in vitro diagnostic device. The 'ground truth' for validating the performance of this device is consistently the CLSI broth microdilution reference method, which is the gold standard for antimicrobial susceptibility testing. Any internal development or optimization of the ETEST strip formulation would also rely on this or similar established reference methods to guide product development.
§ 866.1640 Antimicrobial susceptibility test powder.
(a)
Identification. An antimicrobial susceptibility test powder is a device that consists of an antimicrobial drug powder packaged in vials in specified amounts and intended for use in clinical laboratories for determining in vitro susceptibility of bacterial pathogens to these therapeutic agents. Test results are used to determine the antimicrobial agent of choice in the treatment of bacterial diseases.(b)
Classification. Class II (performance standards).