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Affinity Biosensors Targeting Rapid Susceptibility Testing by Measuring Microbe Mass

NEW YORK ─ Affinity Biosensors is developing an antimicrobial susceptibility testing platform to enable hospitals to make quicker decisions about prescribing antibiotics for patients with bloodstream infections.

The firm leverages resonant suspended cantilevers that measure the mass and concentration of microbes to provide results for the susceptibility of a pathogen to an antibiotic about four hours after a positive blood culture.

The Santa Barbara, California-based company is completing a clinical validation study, using samples from more than 1,000 patients, in preparation for a submission for 510(k) clearance of its AST system with the US Food and Drug Administration, Ken Babcock, the firm's CEO, said in an interview. The company is nearing completion of the clinical study and expects to soon file for FDA clearance.

In the study, results from the firm's AST system are expected to agree with the comparison method, broth microdilution, a high percentage of the time. The system demonstrated high performance using hundreds of patient samples in a pre-clinical portion of the study, and "we anticipate similar performance in the clinical trial," Babcock said. 

The company hopes to get a jump-start on potential adoption by placing systems for evaluation by hospitals toward the end of this year, he said, and sometime next year, it expects to introduce a commercial AST system for hospitals.

Affinity Bios' technology, called LifeScale, is different from other AST systems in development or on the market because it doesn't use a form of light or imaging for detection, Babcock said.

By measuring the mass and concentration of microbes, the firm has figured out how to predict in around four hours whether a pathogen and bug combination in a blood sample is going to survive and replicate after 20 hours of incubation ─ the amount of time needed to definitively determine whether a pathogen is susceptible or resistant to an antibiotic.

"LifeScale uses a very detailed profile of what is going on with the sample, which allows it to correctly assess even the most challenging organisms ─ some of which may not replicate even after several hours of incubation,” Babcock said. "The platform encourages bugs to grow in the presence of different antibiotics and uses different concentrations of the antibiotics to determine which drug suppresses bug growth and at what concentration."

The AST system generates a report consisting of a minimum inhibitory concentration level for the antibiotic-bug combination being tested and calculates whether the combination is categorized as susceptible, intermediate, or resistant. To complete the calculation, the pathogen needs to be identified by a separate instrument, usually a molecular diagnostic system.

Companies such as Luminex, BioMérieux's BioFire, and GenMark Diagnostics supply such molecular testing systems to identify pathogens from bloodstream infections. For example, the BioFire FilmArray Blood Culture Identification panel tests for 24 gram-positive, gram-negative, and yeast pathogens, and three antibiotic resistance genes associated with bloodstream infections. T2 Biosystems' T2Bacteria and T2Candida panels are the only FDA-cleared tests to identify sepsis-causing bacterial and fungal pathogens directly from whole blood without waiting for a blood culture.

All of the molecular diagnostic systems can be used to identify pathogens on the route to determining antimicrobial susceptibility. Labs will be able to implement LifeScale along with any commercially cleared identification instruments, Babcock said.

Its approach has enabled the firm to develop a product that can sit on a hospital bench and fit into clinicians' workflows for antimicrobial susceptibility testing.

Nathan Ledeboer, professor and vice chairman of the department of pathology at the Medical College of Wisconsin, noted that a number of companies are evaluating new AST systems that they are developing and looking to bring to market.

Ledeboer, who has consulted for Affinity Bio and other blood-culture diagnostic companies, noted that overall, hospitals need susceptibility testing results provided "in a cost effective and accurate manner much earlier in the course of disease." If new rapid phenotypic systems, such as the one being developed by Affinity Bio, can show clinical utility in validation studies, they could see adoption by hospitals looking to detect and manage organisms that are especially resistant to antibiotics, he said.

Gradientech, Q-linea, and QuantaMatrix are among companies developing rapid AST systems, and Accelerate Diagnostics has been in the market since 2017 with an FDA-cleared Pheno ID-AST system and kit for bloodstream infections. The firm on Wednesday received FDA clearance for additions that improve its system's performance and expand its antimicrobial susceptibility testing menu for bloodstream infections.

Clinicians tend to immediately treat patients suspected of having a bloodstream infection with an antibiotic that covers a broad spectrum of pathogens, fearful of missing a potentially fatal pathogen. However, such a broad-spectrum approach can miss the mark on the antibiotic that will best benefit the patient and, overall, the practice contributes to antimicrobial resistance.

In treating a patient with a suspected bloodstream infection, laboratorians usually incubate the patient's blood sample to see whether pathogenic organisms will grow in a broth dilution and produce a positive result. From there, they run a test to identify the pathogen and, in parallel, run an antimicrobial susceptibility test.

Most hospitals doing AST testing use systems from established in vitro diagnostic industry companies, such as Beckman Coulter, BioMérieux, Becton Dickinson, and Thermo Fisher Scientific. These are high-performing systems that provide antimicrobial susceptibility test results after a blood culture has confirmed that a pathogen is in the blood. However, getting an AST result can take anywhere from 12 hours to a couple of days to accomplish, leaving room in the market for rapid systems that can be deployed when a delay in receiving the correct therapy can be fatal, Babcock said. Affinity Bio believes that with a four-hour turnaround time after a positive blood culture, its system will be among the fastest in the market.

Detecting cell mass

The use of microcantilevers that detect cell mass ─ the technology underpinning LifeScale ─  "has been an area of potential promise in the antimicrobial susceptibility space for about a decade, because it provides the potential to get early results and be very accurate in those measurements," Ledeboer said.

Such systems are needed, in particular, to test gram-negative organisms, which are far more challenging than gram-positive organisms when it comes to obtaining an AST result, he said, adding, "The number of ways you can get antibiotic resistance from gram-negative organisms can number in the thousands for some drugs, and detecting them is far more challenging than finding a few gram-positive resistance determinants" that may cause methicillin-resistant Staphylococcus aureus, for example.  

Babcock noted that Affinity Biosensors is designing its first AST product to address most gram-negative organisms because he believes the greatest unmet market need lies in supplying products for that application.

In future generation products, the firm plans to expand to the testing of gram-positive organisms as well as yeast organisms, leveraging its current platform. A future product on the drawing board would operate directly from whole blood with an aim of providing an AST result in less than nine hours from the time of a blood draw, Babcock said.

Using a direct sales team to target customers, the firm has engaged with undisclosed early adopters that intend to begin conducting technology evaluations around the end of the year. To increase the system's potential for adoption, Affinity Bio expects to offer more affordable antimicrobial susceptibility testing to hospitals, Babcock said. Hospitals would be able to use the system without an outlay of capital and pay Affinity Bio to rent reagents, a business model employed by many diagnostic companies. The pricing of its tests is likely to be aligned with that of current molecular diagnostic tests, he added.

While the firm's eye is on getting FDA clearance and then targeting the 1,500 hospitals in the US that could implement its system, Babcock said Affinity Bio also plans to expand to other geographies, including Europe, Asia, and Central America.