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Diagnostics Firm TGV-Dx Aims for Faster, Broader Antibiotic Susceptibility Testing


NEW YORK – New York City-based diagnostic company TGV-Dx has developed an antibiotic susceptibility testing method it claims can overcome two key hurdles in the industry: speed and breadth.

With its AtbFinder assay, the firm is attempting to address turnaround time and accuracy issues found in more traditional methods of antibiotic susceptibility testing, such as disk diffusion assays, which can take more than 48 hours to return results due to their reliance on slow-growing bacterial cultures, CEO George Tetz said in an interview. In addition, those techniques often only identify the lead pathogen causing an infection, leaving a host of other bacteria that could help determine an acceptable antibiotic treatment unidentified.

Traditional techniques typically use pure cultures targeted to the lead pathogen of an infection and take 24 to 48 hours to grow. Once the pure culture is obtained, studying the effects of different antibiotics can take another 12 hours, meaning up to 60 hours can pass before a final decision is made that only accounts for the lead pathogen, he added. 

But in the "vast majority" of infections, those lead pathogens don't grow alone, Tetz said. They are "surrounded by many other types of bacteria that help these lead pathogens withstand antibiotic assault." Many conventional methods miss the "complicated inter-bacterial reactions" that can affect the antibiotic response, he said.

Tetz and collaborators from a variety of institutions, including the New York Genome Center and New York University, studied previously unculturable bacterial species and were able to develop a novel growth medium — the backbone of TGV's AtbFinder method — that enables the simultaneous growth of multiple kinds of bacteria and allows them to start growing within four hours. Instead of studying "only the lead bacterial pathogen in these very constrained settings," the team decided to study the response of the "entire bacterial community" to different antibiotics, he said.

When running the test, samples are placed onto a multiwell plate filled with the novel growth medium that captures all bacterial growth from the site of an infection. Different wells are supplemented with antibiotics at concentrations that are tailored to the infection site, and depending on the number of plates used, up to 188 antibiotics — including single and multiple drug combinations — can be tested at one time, Tetz said. After the samples are incubated, results can be obtained either through the naked eye or an automated scanner with no additional equipment required, he added. The data analysis itself is not different from other conventional methods like disk diffusion, Tetz noted. 

Reducing turnaround times and increasing automation for antibiotic susceptibility testing have been the focus of many diagnostic companies in recent years. Accelerate Diagnostics offers multiple configurations of its AST solutions, some of which return results in about seven hours, and recently launched its Accelerate Arc platform that automates microbial identification of positive blood cultures.

BioMérieux, meantime, acquired Specific Diagnostics and its rapid metabolomics-based AST system last year and has a suite of other solutions, such as its Vitek MS mass spectrometry systems, for microbial identification and susceptibility testing. 

Other companies in the space rely on PCR-based methods, such as OpGen subsidiary Curetis' Unyvero platform, or microfluidics, like Gradientech and Scope Fluidics, both of which have received CE marking for their antimicrobial susceptibility tests.

And smaller firms such as Avails Medical and Day Zero Diagnostics have received millions in funding from the Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator for new platforms that shrink turnaround times to a few hours.

Although the speed of AtbFinder is a selling point, Tetz said that the benefits of the test are less about the speed and more about the increased accuracy of antibiotic selection that's possible with AtbFinder. It's "not only about the speed, it's about the overall principle" behind the platform that makes it unique, he said.

A paper published in Microorganisms in 2021 that describes the development of the method and its use in respiratory infections found the test had nearly 100 percent sensitivity and 98 percent specificity in monomicrobial specimens after four hours of growth. The same paper found that in polymicrobial specimens, the test enabled accurate selection of antibiotics that "completely eliminated all cultivatable bacteria" within four hours.

A paper published earlier this year in the Journal of Clinical Microbiology found that AtbFinder was able to reduce the number of systemic antibiotic courses used in 35 cystic fibrosis patients from 355 to 178. The antibiotic regimens selected through use of AtbFinder also showed superior performance compared to those selected with routine testing, the authors noted.

Michael Mahan, a professor in the molecular, cellular, and developmental biology department at the University of California, Santa Barbara who has not worked with the company, noted via email that a difficulty for any in vitro test for antibiotic selection is that antibiotic potency is "highly context-dependent, influenced by media composition, pathogen factors, and host factors that can act synergistically with antimicrobials." With that being said, he added that AtbFinder had "very good performance" in both the identification of appropriate antibiotics after four or 24 hours of culturing and in the identification of appropriate antibiotics for polymicrobial infections.

AtbFinder is not yet available commercially, but TGV-Dx is establishing a CLIA-certified laboratory to register it as a laboratory-developed test, which will be the fastest pathway to making it available. That lab will likely be outside the company's home base, since New York state's laboratory regulations are among the most stringent in the country, he said. The company is also looking to collaborate with New York-based labs that already have CLIA certification to implement the test as an LDT. 

For infections where time is of the essence, accessing the technology as an LDT won't have much use since clinicians wouldn't have the leeway to ship samples to another lab and wait for results, but Tetz noted that other kinds of infections, such as recurrent urinary tract infections, have fewer time constraints and could be shipped to the TGV-Dx lab for testing.

For those infections that do need results quickly, the company also intends to pursue 510(k) clearance from the US Food and Drug Administration for AtbFinder, which would allow it to sell the assay as an in vitro diagnostic kit and make it available to more users. The firm would also potentially work with a larger distributor once the FDA clearance is received because it would be more efficient, he said. 

TGV-Dx has also been working with a reimbursement expert to determine what it needs for coverage from the Centers for Medicare and Medicaid Services, but Tetz said the test will likely be priced on the higher side of traditional methods, but less than the majority of metagenomic sequencing methods, which costs around $2,000. 

The company has different tests for different types of infections, such as skin, soft tissue, urinary tract, and respiratory infections, and it is also working on a version for fungal infections, he said.