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The MTS (MIC Test Strip) Sulbactam-Durlobactam 0.004/4-64/4 μg/ml is a quantitative method intended for the in vitro determination of antimicrobial susceptibility of bacteria. MTS consists of specialized paper impregnated with a pre-defined concentration gradient of an antimicrobial agent, which is used to determine the minimum inhibitory concentration (MIC) in μg/ml of antimicrobial agents against bacteria as tested on agar media using overnight incubation and manual reading procedures. MTS Sulbactam- Durlobactam at concentrations of 0.004/4-64/4 μg/ml should be interpreted at 16-20 hours of incubation.

Testing with MTS Sulbactam-Durlobactam at concentrations of 0.004/4-64/4 μg/mL is indicated for Acinetobacter baumannii calcoaceticus complex as recognized by the FDA Susceptibility Test Interpretive Criteria (STIC).

The MTS Sulbactam-Durlobactam 0.004/4-64/4 μg/mL has demonstrated acceptable performance with the following organisms:

Acinetobacter baumannii calcoaceticus complex

MTS Sulbactam-Durlobactam 0.004/4 - 64/4 μg/mL is made of special high-quality paper impregnated with a predefined concentration of gradient sulbactam across 15 two-fold dilutions like those of a conventional MIC method and durlobactam at a fixed concentration of 4 μg/mL. One side of the strip is labeled with the sulbactam-durlobactam code (SUD) and the MIC reading scale in μg/mL. When the MTS is applied onto an inoculated agar surface, the performed exponential gradient of antimicrobial agent diffuses into the agar for over an hour. After 16-20 hours incubation, a symmetrical inhibition ellipse centered along the strip is formed. The MIC is read directly from the scale in terms of μg/mL at the point where the edge of the inhibition ellipse intersects the MIC Test Strip. The MIC Test Strip (MTS) is single use only.

Sulbactam-durlobactam is an intravenous beta-lactam combination antibiotic used to treat hospital-acquired pneumonia and ventilator-associated bacterial pneumonia caused by susceptible isolates of Acinetobacter baumannii-calcoaceticus complex.
MTS is supplied in 3 different packaging options (no additional reagents are included). There is a 10- test box, a 30- test box and a 100-test box.

Here is a description of the acceptance criteria and the study proving the device meets those criteria, based on the provided FDA 510(k) clearance letter for the MTS Sulbactam-Durlobactam device:

Device: MTS Sulbactam-Durlobactam 0.004/4 - 64/4 µg/mL (SUD)
Intended Use: Quantitative method for in vitro determination of antimicrobial susceptibility of Acinetobacter baumannii calcoaceticus complex using MIC Test Strips with manual reading after overnight incubation.

1. Acceptance Criteria and Reported Device Performance

The study evaluated the performance of the MTS Sulbactam-Durlobactam device against a reference broth microdilution MIC method. The primary metrics for performance were Essential Agreement (EA) and Category Agreement (CA), along with an analysis of errors (very major, major, minor). While explicit "acceptance criteria" percentages are not directly stated in the summary, typical FDA criteria for AST systems are implied by the reported results. The guidance document referenced "Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems, August 28, 2009" would contain the specific acceptance thresholds. Based on the provided summary, the device performance is reported as follows:

Table of Device Performance

Implied Acceptance Criteria (based on typical FDA AST requirements, generally >90% for EA and CA, and strict limits on major/very major errors):
The reported performance values of 97.3% EA and 92.7% CA, along with very low major errors and zero very major errors, indicate that the device met the acceptance criteria as determined by the FDA. Specifically, the zero very major errors are critical for patient safety, as they avoid situations where a resistant infection might be incorrectly identified as susceptible, leading to inappropriate treatment.

2. Sample Size and Data Provenance

• Test Set Sample Size: 588 isolates for the combined clinical and challenge organism groups.
• Data Provenance:
  • Clinical Testing: Performed at three (3) sites. The precise country of origin is not explicitly stated for the clinical sites, but the submitter (Liofilchem s.r.l.) is based in Italy, and their contact person for the 510(k) is in Westlake, Ohio, USA. The FDA clearance suggests testing was appropriate for the US market.
  • Challenge Isolate Testing: Performed at one site (Laboratory Specialists, Inc., which is the 510(k) preparer's company in Westlake, Ohio).
  • Nature of Data: The data combines retrospective (challenge isolates specifically selected to ensure MIC range coverage, including resistant isolates) and prospective (fresh clinical isolates tested at multiple sites) elements.

3. Experts Used for Ground Truth and Qualifications

This section does not directly apply as the device is an in vitro diagnostic (IVD) for antimicrobial susceptibility testing, not an imaging AI device requiring expert interpretation of images. The "ground truth" for antimicrobial susceptibility is established by a standardized laboratory method (broth microdilution) rather than human expert consensus on subjective data.

4. Adjudication Method for the Test Set

Adjudication methods (like 2+1, 3+1, etc.) are typically used in studies involving human interpretation or subjective assessments. For this AST device, the ground truth is established by a quantitative, objective laboratory method (CLSI broth microdilution guidelines). Therefore, no human adjudication method was employed for establishing the ground truth of the MIC values. Minor discrepancies or errors between the device and the reference method are simply categorized as such (major, minor, very major errors).

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

An MRMC study is not applicable to this type of device. The MTS Sulbactam-Durlobactam is a manual antimicrobial susceptibility test system that determines the MIC directly. It is not an AI-assisted diagnostic imaging system where human readers interpret data with or without AI assistance. The performance is assessed by comparing the device's MIC readings to a gold standard laboratory method, not by comparing human reader performance.

6. Standalone (Algorithm Only) Performance

This concept is applicable, and the study provided details on the standalone performance of the MTS Sulbactam-Durlobactam device. The "performance data" table (Essential Agreement, Category Agreement, and Error Rates) directly refers to the device's ability to accurately determine MIC values and susceptibility categories when compared to the reference method, essentially its "algorithm-only" performance in the context of an IVD. There is no "human-in-the-loop" component for interpretation; the user manually reads the MIC from the strip.

7. Type of Ground Truth Used

The ground truth used for this study was reference broth microdilution MIC method, conducted according to CLSI M7-A11 guidelines. This is a well-established and standardized laboratory method for determining antimicrobial minimum inhibitory concentrations, considered the gold standard for AST.

8. Sample Size for the Training Set

The document does not specify a separate "training set" sample size for the development of the MTS Sulbactam-Durlobactam device. For IVDs like AST systems, the "training" typically refers to the initial development and optimization of the test strip's design, antimicrobial gradient, and manufacturing process to reliably produce specific drug concentrations and diffusion patterns. This is primarily a chemical and engineering development process, not a machine learning training process with a distinct data set. The 588 isolates discussed are for the performance validation (test set) rather than initial model training.

9. How Ground Truth for the Training Set Was Established

As noted above, a distinct "training set" and associated "ground truth establishment" in the machine learning sense are not described for this type of medical device. The "ground truth" for the performance validation was established by the CLSI broth microdilution reference method. For the initial development and optimization phase of such a device, the "ground truth" would implicitly be the accurate and precise measurement of drug concentration gradients and their biological effect on various bacterial strains, guided by established AST principles and drug properties.

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