By Ben Butkus
Researchers from Wisconsin's Wheaton Franciscan Healthcare and the University of Wisconsin have published a research paper detailing a cost-saving modification to a commercial real-time PCR assay for detecting methicillin-resistant and –susceptible Staphylococcus aureus in clinical diagnostic labs.
The modification, which involves deep-freezing pre-mixed aliquots of Becton Dickinson's GeneOhm StaphSR assay, is estimated to have reduced their reagent expenditures by some 20 percent, and may encourage a greater number of clinical diagnostic laboratories to consider real-time PCR for detecting MRSA and MSSA, according to the researchers.
Details of the assay modification were published online last week in the Journal of Clinical Microbiology.
GeneOhm MRSA is a qualitative, in vitro, real-time PCR diagnostic test that directly detects MRSA from a nasal specimen. According to the company, the test can be performed in less than two hours, compared to culture methods that require two to five days.
According to the UW-Milwaukee researchers, nucleic acid amplification is the only assay technology able to rapidly delineate MRSA and MSSA from other Gram-positive bacteria in the bloodstream, making it indispensable for guiding appropriate antimicrobial therapy and infection control.
Despite its importance, "some clinical microbiology laboratories may be apprehensive to implement these technologies due to financial considerations" because the "cost of PCR technology may be prohibitive to a number of healthcare institutions," the researchers wrote in their paper.
Erik Munson, technical director at the Wheaton Franciscan Laboratories and corresponding author on the paper, told PCR Insider this week that his laboratory had been using the BD GeneOhm StaphSR assay for MRSA surveillance since the assay was cleared by the US Food and Drug Administration in 2008.
But Munson and colleagues noticed a drawback in the assay that resulted in a significant amount of reagent waste. Specifically, the assay package insert instructs users to reconstitute multiple assay volumes from a single master mix prior to testing.
However, the freshly reconstituted assay is stable for only three hours, and due to the staggered, real-time nature of MRSA testing, multiple aliquots of the assay often go unused — on average, anywhere from 30 to 45 percent of each reagent kit may be wasted, according to the researchers.
So Munson and colleagues decided to test whether deep freezing aliquots of the pre-mixed GeneOhm assay would compromise its effectiveness. They found that both freshly reconstituted master mix and master mix frozen at -70 ºC for as long as six months generated expected results in all PCR reactions.
"It's definitely less waste," Munson told PCR Insider. "We estimate that it saved us upwards of 20 percent in our reagent expenditures."
Added benefits of the freezing step include the fact that it saves time because lab workers can remove pre-mixed assay from the freezer and use it nearly immediately; and may cut down on assay contamination.
Munson said that BD provided his lab with GeneOhm assay supplies in order to conduct the research. "Because this is still off-label use, [BD] really can't sponsor the research completely," he said.
"However, I think their sales people are giving labs the 'wink-wink, nod-nod' to do something like this, and I think a lot of people are starting to do it," he added.
Diane Kawa, director of scientific affairs with BD's diagnostics division, told PCR Insider this week that the research was investigator-initiated, and as such, BD would typically not actively promote the findings to its customers.
"However, if customers inquire about it, we will direct them to Erik because it is an off-label use," Kawa said. "We can share his findings, and will direct customers to them."
She added that BD has yet to do a cost analysis of the GeneOhm StaphSR assay based on the findings, and thus she could not comment on the potential cost reduction that might result from the procedure.
But Munson said that implementing the procedure "could really help a small lab," since most MRSA testing is not reimbursed well by insurance companies, and some labs "take the brunt of the cost in active MRSA surveillance."
Munson and colleagues are currently conducting a study to see if the same protocol can be applied to the GeneOhm CDiff assay for detecting the C. difficile toxin B gene in clinical samples.