Thermo Scientific Oxoid Antimicrobial Susceptibility Test Discs are used in the semi-quantitative agar diffusion test method for in vitro susceptibility testing. Used in a diagnostic workflow to aid clinicians in determining potential treatment options for patients suspected of having a microbial infection, these discs are intended to determine susceptibility against microorganisms for which specific drugs have been shown to be active both clinically and in vitro.

The Thermo Scientific Oxoid Aztreonam/Avibactam Disc (30/20 µg) AZA50 is intended to determine susceptibility of Enterobacterales to Aztreonam/Avibactam, as recognized by the FDA Susceptibility Test Interpretive Criteria (STIC). The Thermo Scientific Oxoid Aztreonam/Avibactam Disc (30/20 µg) AZA50 demonstrated acceptable performance to determine susceptibility to Aztreonam/Avibactam against the following microorganisms:

Enterobacterales (Citrobacter freundii complex, Escherichia coli, Enterobacter cloacae complex, Klebsiella pneumoniae, Klebsiella oxytoca, Serratia marcescens, and Proteus mirabilis)

Device Description

Thermo Scientific Oxoid Aztreonam/Avibactam Disc (30/20 µg) AZA50

AI/ML Overview

The provided FDA 510(k) clearance letter pertains to an Antimicrobial Susceptibility Test Disc (ASTD), specifically the "Thermo Scientific Oxoid Aztreonam/Avibactam Disc (30/20 µg) AZA50". This type of device is a diagnostic tool used in microbiology laboratories to determine how effective certain antimicrobials are against specific microbial infections.

The information typically requested for AI/ML-based medical devices (such as acceptance criteria, ground truth establishment for training/test sets, sample sizes, MRMC studies, etc.) is not directly applicable to this type of traditional in vitro diagnostic device (IVD).

Here's why and what can be extracted from the document:

Nature of the Device: The Aztreonam/Avibactam Disc is a physical disc impregnated with antimicrobial agents. Its "performance" refers to its ability to accurately measure the zone of inhibition (a clear area around the disk where bacteria do not grow), which then correlates to the susceptibility or resistance of the microorganism to the antibiotic. It's not an AI/ML algorithm that interprets or processes complex images or data in an automated way.
Acceptance Criteria for ASTDs: For ASTDs, acceptance criteria typically involve demonstrating a high degree of correlation between the zone diameters produced by the disc and the Minimum Inhibitory Concentration (MIC) values obtained by a reference method (e.g., broth microdilution). This often involves:
- Essential Agreement (EA): The percentage of isolates for which the disc test and the reference method produce results that categorize the isolate into the same interpretive category (Susceptible, Intermediate, Resistant).
- Category Agreement (CA): A stricter measure, where both the zone diameter and MIC fall within defined ranges for a specific category.
- Major Discrepancies (MD): When the disc test indicates Susceptible, but the reference method indicates Resistant.
- Very Major Discrepancies (VMD): When the disc test indicates Resistant, but the reference method indicates Susceptible.
- Minor Discrepancies (mD): Discrepancies between Intermediate and Susceptible/Resistant categories.
  The FDA expects these discrepancy rates to be below certain thresholds (e.g., VMD < 1.5% to 3.0%, MD < 3.0%).
Study Design for ASTDs: Studies for ASTDs involve testing a diverse collection of bacterial isolates (both wild-type and resistant strains) with the new disc and a reference method. The "ground truth" is typically the reference method's result (e.g., standard broth microdilution or agar dilution).

Therefore, I cannot provide the requested information in the format tailored for AI/ML devices because the provided document is for a traditional diagnostic device.

However, based on general knowledge of IVD submissions, here's what could be inferred and what the document explicitly states:

Inferences for Traditional IVDs (not explicitly stated in the provided text):

Acceptance Criteria and Reported Performance (Hypothetical for ASTD):

Acceptance Criteria	Reported Device Performance (Hypothetical)
Essential Agreement (EA) ≥ 90%	EA: 96%
Category Agreement (CA) ≥ 90%	CA: 95%
Very Major Discrepancies (VMD) ≤ 1.5%	VMD: 0.8%
Major Discrepancies (MD) ≤ 3.0%	MD: 1.5%
Minor Discrepancies (mD) ≤ 20%	mD: 10%

Sample Size for Test Set: Typically hundreds to thousands of diverse clinical isolates (e.g., 200-500 isolates per species-drug combination, often more for certain categories like resistant isolates).
- Data Provenance: Usually a mix of retrospective and prospective clinical isolates from various geographic regions (e.g., multiple clinical sites in the US, Europe, etc.) to ensure diversity in resistance mechanisms and strains.
Number of Experts for Ground Truth: Not applicable in the context of human "experts" establishing truth from images/clinical data. The "ground truth" is established by a reference laboratory method (e.g., CLSI or ISO standard broth microdilution) performed by trained microbiologists.
Qualifications of Experts: Trained microbiologists and laboratory technicians following standardized protocols for the reference method.
Adjudication Method: Not applicable. The reference method is the "truth," and results are compared directly to it.
Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study: Not applicable to this type of device. There are no human "readers" of an AI output to compare.
Standalone Performance: The "standalone performance" of the disc is its correlation with the reference method.
Type of Ground Truth Used: Standardized reference antimicrobial susceptibility testing methods (e.g., broth microdilution or agar dilution) and established FDA Susceptibility Test Interpretive Criteria (STIC).
Sample Size for Training Set: Not applicable for a traditional ASTD; there's no "training" in the ML sense. The formulation of the disc and preliminary testing would involve screening many isolates, but not in an ML training paradigm.
How Ground Truth for Training Set was Established: Not applicable.

What the document does tell us:

Device Identity: Thermo Scientific Oxoid Aztreonam/Avibactam Disc (30/20 µg) AZA50.
Intended Use: Used in the semi-quantitative agar diffusion test method for in vitro susceptibility testing to aid clinicians in determining potential treatment options for patients suspected of having a microbial infection. Specifically, it's intended to determine susceptibility of Enterobacterales to Aztreonam/Avibactam, as recognized by the FDA Susceptibility Test Interpretive Criteria (STIC).
Microorganisms for which performance was demonstrated: Enterobacterales (Citrobacter freundii complex, Escherichia coli, Enterobacter cloacae complex, Klebsiella pneumoniae, Klebsiella oxytoca, Serratia marcescens, and Proteus mirabilis).
Regulatory Classification: Class II, Product Code JTN, Regulation Number 21 CFR 866.1620 (Antimicrobial Susceptibility Test Disc).
Performance Statement: "The Thermo Scientific Oxoid Aztreonam/Avibactam Disc (30/20 µg) AZA50 demonstrated acceptable performance to determine susceptibility to Aztreonam/Avibactam against the following microorganisms:" (followed by the list of microorganisms). This statement implies that the manufacturer successfully met the pre-defined acceptance criteria for performance validation.

In summary, the provided document clears a traditional in-vitro diagnostic device, not an AI/ML powered one, meaning the requested detailed information about AI/ML study methodologies is not present nor relevant for this product.

Summary

U.S. Food & Drug Administration

10903 New Hampshire Avenue
Doc ID # 04017.07.05
Silver Spring, MD 20993
www.fda.gov

June 12, 2025

Thermo Fisher Scientific (Oxoid Ltd.)
Shilpa Bhalerao
Scientist II (Clinical Trials Specialist)
Wade Road
Basingstoke, Hampshire RG24 8PW
United Kingdom

Re: K250789
Trade/Device Name: Thermo Scientific Oxoid Aztreonam/Avibactam Disc (30/20 µg) AZA50
Regulation Number: 21 CFR 866.1620
Regulation Name: Antimicrobial Susceptibility Test Disc
Regulatory Class: Class II
Product Code: JTN
Dated: February 17, 2025
Received: March 14, 2025

Dear Shilpa Bhalerao:

We have reviewed your section 510(k) premarket notification of intent to market the device referenced above and have determined the device is substantially equivalent (for the indications for use stated in the enclosure) to legally marketed predicate devices marketed in interstate commerce prior to May 28, 1976, the enactment date of the Medical Device Amendments, or to devices that have been reclassified in accordance with the provisions of the Federal Food, Drug, and Cosmetic Act (the Act) that do not require approval of a premarket approval application (PMA). You may, therefore, market the device, subject to the general controls provisions of the Act. Although this letter refers to your product as a device, please be aware that some cleared products may instead be combination products. The 510(k) Premarket Notification Database available at https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm identifies combination product submissions. The general controls provisions of the Act include requirements for annual registration, listing of devices, good manufacturing practice, labeling, and prohibitions against misbranding and adulteration. Please note: CDRH does not evaluate information related to contract liability warranties. We remind you, however, that device labeling must be truthful and not misleading.

If your device is classified (see above) into either class II (Special Controls) or class III (PMA), it may be subject to additional controls. Existing major regulations affecting your device can be found in the Code of Federal Regulations, Title 21, Parts 800 to 898. In addition, FDA may publish further announcements concerning your device in the Federal Register.

FDA's substantial equivalence determination also included the review and clearance of your Predetermined Change Control Plan (PCCP). Under section 515C(b)(1) of the Act, a new premarket notification is not required for a change to a device cleared under section 510(k) of the Act, if such change is consistent with an established PCCP granted pursuant to section 515C(b)(2) of the Act. Under 21 CFR 807.81(a)(3), a new

U.S. Food & Drug Administration
10903 New Hampshire Avenue
Silver Spring, MD 20993
www.fda.gov

June 12, 2025

Thermo Fisher Scientific (Oxoid Ltd.)
Shilpa Bhalerao
Scientist II (Clinical Trials Specialist)
Wade Road
Basingstoke, Hampshire RG24 8PW
United Kingdom

Dear Shilpa Bhalerao:

U.S. Food & Drug Administration
10903 New Hampshire Avenue
Silver Spring, MD 20993
www.fda.gov

Page 2

K250789 - Shilpa Bhalerao Page 2

premarket notification is required if there is a major change or modification in the intended use of a device, or if there is a change or modification in a device that could significantly affect the safety or effectiveness of the device, e.g., a significant change or modification in design, material, chemical composition, energy source, or manufacturing process. Accordingly, if deviations from the established PCCP result in a major change or modification in the intended use of the device, or result in a change or modification in the device that could significantly affect the safety or effectiveness of the device, then a new premarket notification would be required consistent with section 515C(b)(1) of the Act and 21 CFR 807.81(a)(3). Failure to submit such a premarket submission would constitute adulteration and misbranding under sections 501(f)(1)(B) and 502(o) of the Act, respectively.

Additional information about changes that may require a new premarket notification are provided in the FDA guidance documents entitled "Deciding When to Submit a 510(k) for a Change to an Existing Device" (https://www.fda.gov/media/99812/download) and "Deciding When to Submit a 510(k) for a Software Change to an Existing Device" (https://www.fda.gov/media/99785/download).

Your device is also subject to, among other requirements, the Quality System (QS) regulation (21 CFR Part 820), which includes, but is not limited to, 21 CFR 820.30, Design controls; 21 CFR 820.90, Nonconforming product; and 21 CFR 820.100, Corrective and preventive action. Please note that regardless of whether a change requires premarket review, the QS regulation requires device manufacturers to review and approve changes to device design and production (21 CFR 820.30 and 21 CFR 820.70) and document changes and approvals in the device master record (21 CFR 820.181).

Please be advised that FDA's issuance of a substantial equivalence determination does not mean that FDA has made a determination that your device complies with other requirements of the Act or any Federal statutes and regulations administered by other Federal agencies. You must comply with all the Act's requirements, including, but not limited to: registration and listing (21 CFR Part 807); labeling (21 CFR Part 801 and Part 809); medical device reporting (reporting of medical device-related adverse events) (21 CFR Part 803) for devices or postmarketing safety reporting (21 CFR Part 4, Subpart B) for combination products (see https://www.fda.gov/combination-products/guidance-regulatory-information/postmarketing-safety-reporting-combination-products); good manufacturing practice requirements as set forth in the quality systems (QS) regulation (21 CFR Part 820) for devices or current good manufacturing practices (21 CFR Part 4, Subpart A) for combination products; and, if applicable, the electronic product radiation control provisions (Sections 531-542 of the Act); 21 CFR Parts 1000-1050.

All medical devices, including Class I and unclassified devices and combination product device constituent parts are required to be in compliance with the final Unique Device Identification System rule ("UDI Rule"). The UDI Rule requires, among other things, that a device bear a unique device identifier (UDI) on its label and package (21 CFR 801.20(a)) unless an exception or alternative applies (21 CFR 801.20(b)) and that the dates on the device label be formatted in accordance with 21 CFR 801.18. The UDI Rule (21 CFR 830.300(a) and 830.320(b)) also requires that certain information be submitted to the Global Unique Device Identification Database (GUDID) (21 CFR Part 830 Subpart E). For additional information on these requirements, please see the UDI System webpage at https://www.fda.gov/medical-devices/device-advice-comprehensive-regulatory-assistance/unique-device-identification-system-udi-system.

Also, please note the regulation entitled, "Misbranding by reference to premarket notification" (21 CFR 807.97). For questions regarding the reporting of adverse events under the MDR regulation (21 CFR Part

Page 3

K250789 - Shilpa Bhalerao Page 3

803), please go to https://www.fda.gov/medical-devices/medical-device-safety/medical-device-reporting-mdr-how-report-medical-device-problems.

For comprehensive regulatory information about medical devices and radiation-emitting products, including information about labeling regulations, please see Device Advice (https://www.fda.gov/medical-devices/device-advice-comprehensive-regulatory-assistance) and CDRH Learn (https://www.fda.gov/training-and-continuing-education/cdrh-learn). Additionally, you may contact the Division of Industry and Consumer Education (DICE) to ask a question about a specific regulatory topic. See the DICE website (https://www.fda.gov/medical-devices/device-advice-comprehensive-regulatory-assistance/contact-us-division-industry-and-consumer-education-dice) for more information or contact DICE by email (DICE@fda.hhs.gov) or phone (1-800-638-2041 or 301-796-7100).

Sincerely,

Ribhi Shawar -S

Ribhi Shawar, Ph.D. (ABMM)
Chief
General Bacteriology and Antimicrobial Susceptibility Branch
Division of Microbiology Devices
OHT7: Office of In Vitro Diagnostics
Office of Product Evaluation and Quality
Center for Devices and Radiological Health

Enclosure

Page 4

FORM FDA 3881 (8/23) Page 1 of 1 PSC Publishing Services (301) 443-6740 EF

DEPARTMENT OF HEALTH AND HUMAN SERVICES
Food and Drug Administration

Indications for Use

Form Approved: OMB No. 0910-0120
Expiration Date: 07/31/2026
See PRA Statement below.

510(k) Number (if known)
K250789

Device Name
Thermo Scientific Oxoid Aztreonam/Avibactam Disc (30/20 µg) AZA50

Indications for Use (Describe)

Enterobacterales (Citrobacter freundii complex, Escherichia coli, Enterobacter cloacae complex, Klebsiella pneumoniae, Klebsiella oxytoca, Serratia marcescens, and Proteus mirabilis)

Type of Use (Select one or both, as applicable)

☒ Prescription Use (Part 21 CFR 801 Subpart D) ☐ Over-The-Counter Use (21 CFR 801 Subpart C)

CONTINUE ON A SEPARATE PAGE IF NEEDED.

This section applies only to requirements of the Paperwork Reduction Act of 1995.
DO NOT SEND YOUR COMPLETED FORM TO THE PRA STAFF EMAIL ADDRESS BELOW.

The burden time for this collection of information is estimated to average 79 hours per response, including the time to review instructions, search existing data sources, gather and maintain the data needed and complete and review the collection of information. Send comments regarding this burden estimate or any other aspect of this information collection, including suggestions for reducing this burden, to:

Department of Health and Human Services
Food and Drug Administration
Office of Chief Information Officer
Paperwork Reduction Act (PRA) Staff
PRAStaff@fda.hhs.gov

"An agency may not conduct or sponsor, and a person is not required to respond to, a collection of information unless it displays a currently valid OMB number."

DEPARTMENT OF HEALTH AND HUMAN SERVICES Form Approved: OMB No. 0910-0120
Food and Drug Administration Expiration Date: 07/31/2026

Indications for Use

                                                                                                                                                                **See PRA Statement below.**

510(k) Number (if known)
K250789

Device Name
Thermo Scientific Oxoid Aztreonam/Avibactam Disc (30/20 µg) AZA50

Indications for Use (Describe)

Enterobacterales (Citrobacter freundii complex, Escherichia coli, Enterobacter cloacae complex, Klebsiella pneumoniae, Klebsiella oxytoca, Serratia marcescens, and Proteus mirabilis)

Type of Use (Select one or both, as applicable)

☒ Prescription Use (Part 21 CFR 801 Subpart D) ☐ Over-The-Counter Use (21 CFR 801 Subpart C)

CONTINUE ON A SEPARATE PAGE IF NEEDED.

This section applies only to requirements of the Paperwork Reduction Act of 1995.
DO NOT SEND YOUR COMPLETED FORM TO THE PRA STAFF EMAIL ADDRESS BELOW.

Department of Health and Human Services
Food and Drug Administration
Office of Chief Information Officer
Paperwork Reduction Act (PRA) Staff
PRAStaff@fda.hhs.gov

"An agency may not conduct or sponsor, and a person is not required to respond to, a collection of information unless it displays a currently valid OMB number."

FORM FDA 3881 (8/23) Page 1 of 1 PSC Publishing Services (301) 443-6740 EF

Regulation Number and Section

§ 866.1620 Antimicrobial susceptibility test disc.

(a)
Identification. An antimicrobial susceptibility test disc is a device that consists of antimicrobic-impregnated paper discs used to measure by a disc-agar diffusion technique or a disc-broth elution technique the in vitro susceptibility of most clinically important bacterial pathogens to antimicrobial agents. In the disc-agar diffusion technique, bacterial susceptibility is ascertained by directly measuring the magnitude of a zone of bacterial inhibition around the disc on an agar surface. The disc-broth elution technique is associated with an automated rapid susceptibility test system and employs a fluid medium in which susceptibility is ascertained by photometrically measuring changes in bacterial growth resulting when antimicrobial material is eluted from the disc into the fluid medium. Test results are used to determine the antimicrobial agent of choice in the treatment of bacterial diseases.(b)
Classification. Class II (performance standards).