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VITEK® 2 AST-Gram Negative Plazomicin is designed for antimicrobial susceptibility testing of Gram negative bacilli and is intended for use with the VITEK® 2 and VITEK® 2 Compact Systems as a laboratory aid in the determination of in vitro susceptibility to antimicrobial agents. VITEK® 2 AST-Gram Negative Plazomicin is a quantitative test. Plazomicin has been shown to be active against most strains of the microorganisms listed below, according to the FDA label for this antimicrobial.

Active both in vitro and in clinical infections: Escherichia coli Klebsiella pneumoniae Enterobacter cloacae

In vitro data are available, but their clinical significance is unknown:

Citrobacter freundii Citrobacter koseri Klebsiella (Enterobacter) aerogenes Klebsiella oxytoca Proteus vulgaris Serratia marcescens

The VITEK® 2 Gram-Negative Susceptibility Card is intended for use with the VITEK® 2 Systems in clinical laboratories as an in vitro test to determine the susceptibility of clinicaly significant aerobic bacilli to antimicrobial agents when used as instructed.

The principle of the VITEK® 2 AST cards is based on the microdilution minimum inhibitory concentration (MIC) technique reported by MacLowry and Marsh(4) and Gerlach(2). The VITEK® 2 AST card is essentially a miniaturized, abbreviated and automated version of the doubling dilution technique(3).

Each VITEK® 2 AST card contains 64 wells. A control well which only contains microbiological culture media is resident on all cards. The remaining wells contain premeasured portions of a specific antibiotic combined with culture media. The isolate to be tested is diluted to a standardized concentration with 0.45 - 0.5% saline before being used to rehydrate the antimicrobial medium within the card. The VITEK® 2 System automatically fills, seals and places the card into the incubator/reader. The VITEK® 2 Compact has a manual filling, sealing and loading operation. The VITEK® 2 Systems monitor the growth of each well in the card over a defined period of time. At the completion of the incubation cycle, a report is generated that contains the MIC value along with the interpretive category result for each antibiotic contained on the card.

This document, K223478, describes the premarket notification for the VITEK® 2 AST-GN Plazomicin antimicrobial susceptibility testing system. The device is intended to determine the in vitro susceptibility of Gram-negative bacilli to Plazomicin.

Here's an analysis of the acceptance criteria and the study proving the device meets them:

1. Table of Acceptance Criteria and Reported Device Performance

The acceptance criteria for antimicrobial susceptibility testing (AST) devices are typically based on Essential Agreement (EA) and Category Agreement (CA), along with limits for Very Major Errors (VME), Major Errors (ME), and Minor Errors (mE), as defined by the FDA Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems. While the document doesn't explicitly state numerical acceptance criteria for each error type (e.g., "VME must be <X%"), it presents the achieved performance.

The reported device performance for Plazomicin testing against Enterobacteriaceae is as follows:

2. Sample Size Used for the Test Set and Data Provenance

• Sample Size for Test Set: The number of isolates tested for performance evaluation against the "FDA (CLSI)" breakpoint (which signifies the primary clinical evaluation) was 858 isolates. Additionally, reproducibility was tested, but the sample size for that specific test is not explicitly broken down beyond the 97.0% result.
• Data Provenance: The study involved an "external evaluation" conducted with "fresh and stock clinical isolates, as well as a set of challenge strains." This suggests a prospective collection of isolates for the study, encompassing both routine clinical samples and specific strains designed to challenge the system. The document does not specify the country of origin of the data.

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications

This document describes a diagnostic device that performs Antimicrobial Susceptibility Testing (AST). For AST devices, the "ground truth" is typically established by a reference method, not human experts in the way it would be for imaging interpretation.

• Ground Truth Establishment: The ground truth for the test set was established by the CLSI Broth Microdilution reference method. This is an internationally recognized standard laboratory procedure for determining minimum inhibitory concentrations (MICs) of antimicrobials.
• Number and Qualifications of Experts: There were no human experts establishing the ground truth for this type of test by consensus reading. The ground truth is a laboratory measurement performed according to a standardized protocol.

4. Adjudication Method for the Test Set

Since the ground truth is established by a standardized laboratory reference method (CLSI Broth Microdilution), no adjudication method (like 2+1 or 3+1 consensus) was used or needed in the traditional sense for diagnostic systems relying on human interpretation. The comparison is directly between the device's output and the MIC values from the reference method.

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

No MRMC comparative effectiveness study was mentioned or performed. This device is an automated laboratory instrument for determining antimicrobial susceptibility, not an imaging AI tool designed to assist human readers. Therefore, the concept of human readers improving with AI assistance is not applicable here.

6. Standalone (Algorithm Only Without Human-in-the-Loop Performance) Study

Yes, a standalone performance study was conducted. The VITEK® 2 AST-GN Plazomicin system, including its "Growth Pattern Analysis (GPA)" algorithms, performs the susceptibility testing automatically. The performance metrics (Essential Agreement, Category Agreement, and Error Rates) presented in Table 2 are the direct output of the device compared to the reference method, without human intervention in the interpretation of the VITEK 2 results themselves.

7. Type of Ground Truth Used

The type of ground truth used was an established laboratory reference method: the CLSI Broth Microdilution method. This method provides quantitative Minimum Inhibitory Concentration (MIC) values, which are then categorized (Susceptible, Intermediate, Resistant) based on breakpoints.

8. Sample Size for the Training Set

The document does not provide information on the sample size for a training set. For AST devices, the "training" of the algorithm typically involves a robust development process using a large library of characterized isolates to optimize the growth pattern analysis (GPA) algorithms to accurately predict MICs. This development phase is usually distinct from the clinical validation study described here. The 858 isolates represent the test set for performance validation.

9. How the Ground Truth for the Training Set Was Established

The document does not describe how the ground truth for the training set (if a distinct one was used for specific algorithm development) was established. However, it's highly probable that similar to the test set, the ground truth for any algorithm development or "training" would also rely on established reference methods like CLSI Broth Microdilution to characterize the isolates used in that phase.

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