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Nanosphere Releases Data on Gram-Positive Blood Culture Test Ahead of Anticipated FDA Approval


By Molika Ashford

Nanosphere's new gram-positive blood culture test performs with very high accuracy, according to researchers from the company and the Medical College of Wisconsin who presented data at the Interscience Conference on Antimicrobial Agents and Chemotherapy in Chicago last month.

The team, led by Nathan Ledeboer, a professor of pathology at MCW and a Nanosphere consultant, reported in a poster that the BC-GP assay achieved 98 percent sensitivity in identifying bacterial targets in samples, and 100 percent sensitivity and specificity in recognizing antibiotic-resistant bacteria.

Nanosphere is about a month away from completing a 1,000-sample trial, also led by Ledeboer, that will make up the backbone of its application for US Food and Drug Administration approval for the assay. The data presented at the meeting was derived from a separate 60 blood culture samples.

The BC-GP assay "didn't really miss anything and agreed with culture in basically every instance," Ledeboer told BioArray News.

According to Michael McGarrity, Nanosphere's vice president of sales and chief marketing officer, the Northbrook, Ill.-based company believes that the microbiology space is "poised for conversion from traditional culture methods to more advanced rapid diagnosis."

Currently, he told BioArray News, bacterial infections are diagnosed through blood culture in a step-wise process that can take days. In the meantime, patients are treated with broad-spectrum antibiotics. "The current standard is to treat prophylactically … and then by the time they get the information 72 hours later it doesn’t direct therapy," McGarrity said.

"By taking a positive blood culture and running it directly into our assay, we can now provide [an answer] in two and half hours from positive blood culture, as opposed to 36 to 72 hours or even days."

The MCW study analyzed 60 blood samples using the Verigene BC-GP assay, which targets 13 bacterial species, as well as two determinants of antibiotic resistance — mecA and vanA/B.

"One of the benefits of our technology is our multiplexing capability," he said. "So we are able to provide… both identification and resistance markers. That’s based on our microarray technology that allows us to put down numerous targets to capture both identification and resistance," said McGarrity.

The BC-GP assay is run on Nanosphere's Verigene SP system, a sample-to-result benchtop workstation that uses gold nanoparticle technology to detect nucleic acid and protein targets of interest for a variety of applications.

In their poster, the researchers reported that the results of the BC-GP panel were concordant with biochemical detection in 55 of 57 positive blood cultures. In one of five cultures containing two organisms, the assay only identified one of the two present. Overall, this translated to a sensitivity of 98.4 percent, the team wrote.

For resistance, the test showed 100 percent sensitivity and specificity, they reported, predicting oxacillin resistance in 34 Staphylococcus samples and vacomycin resistance in 10 Enterococcus samples.

According to McGarrity, with this level of performance, the test offers competitive accuracy to the long culturing process, but with the added advantage of speed, something he said is necessary to allow for better patient care and more targeted therapy.

"The potential is there to improve outcomes from a morbidity and mortality standpoint, [as well as] economic benefits of reduced length of stay and antimicrobial stewardship," he said.

"The aim of a lot of these treatments is to reduce resistance, and by targeting a therapy you are going to empirically get better outcomes, as well as reduce cost," he added.

Ledeboer said he agrees.

"Today a patient is going to get put on vacomycin or daptomycin empirically, and both those drugs are expensive and require that the patient remain in intensive care until [the physician] can figure out what [the organism] is."

"What this is going to allow you to do is, once that blood culture is positive, within a couple of hours you're going to be able to de-escalate that patient."

Ledeboer cited a study published last year by researchers at Ohio State University that looked at a PCR test for methicillin-resistant and methicillin-sensitive Staphylococcus aureus and showed that this kind of rapid result could reduce the cost of hospitalization by more than $21,000, reduce the length of stay by more than six days, and reduce the amount of time before switching from vacomycin by 1.7 days.

"If you imagine just being able to do that with a single PCR, the potential is even greater with a larger array of targets like the Nanosphere system has," he said.

Ledeboer ceded that Nanosphere is not the only company trying to improve on the standard culture method for identifying bacterial pathogens and noted that Idaho Technology, Luminex, and other firms are working on similar tests. "There is also the possibility that MALDI-TOF [mass spectrometry] could play a significant role in this type of a situation," he said.

The MCW researchers are planning to present a poster at the upcoming Infectious Diseases Society of America meeting that examines the performance of MALDI-TOF "with some clinical data," he added. "I can't share that yet, but I can tell you that there are plusses and minuses to [the mass spectrometry] approach versus something like the Nanosphere assay."

"One of the plusses is that [MALDI-TOF] is a little bit faster," he said. "One main minus is that if you have two organisms, MALDI can't distinguish."

Ledeboer said that he and his colleagues plan to continue comparisons of the Nanosphere test against other methods. "Those are studies that are going to be ongoing through the remainder of this year and into next year for us," he said.

McGarrity said that Nanosphere feels confident about its position in the FDA clearance process. The company has made its initial submission to the FDA for the BC-GP assay and feels that this puts them somewhat "ahead" of competitors in the market.

"We don't anticipate we'll be the only player in the space, but we think we have two advantages. One is that we're in the process of obtaining FDA clearance, though we can't predict the timing of that," said McGarrity. "Also, we feel that that we have a unique capability based on the proprietary aspects of our technology to provide a sample-to-result assay with multiplexing capability in an on-demand format. Those are really the keys," he said.

In addition to the BC-GP test, Nanosphere in January received clearance for a respiratory viral assay on the Verigene platform and is continuing work on a gram-negative assay, a Clostridium difficile assay, and an enteric panel for pathogens in stool samples, McGarrity said.

The BC-GP assay is also awaiting CE-IVD clearance in Europe.

Have topics you'd like to see covered in BioArray News? Contact the editor at mashford [at] genomeweb [.] com.

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