A Simple Swap Could Change How Hospitals Test Antibiotics for Drug-Resistant Infections

New Method Accelerates Testing for Drug‑Resistant Infections

BOSTON — Microbiologists at Beth Israel Deaconess Medical Center (BIDMC) have developed a faster, simpler way to test whether antibiotics will work against drug-resistant bacterial infections. The elegant method could save patients precious time while supporting responsible use of the antibiotic arsenal.

In a study published in the Journal of Clinical Microbiology, a team led by James E. Kirby, MD, director of the Clinical Microbiology Laboratory at BIDMC, showed that simply changing the materials in a standard lab test to grow bacteria can deliver gold-standard results in a fraction of the time and with less effort.

“Our technology provides a simple way for standard clinical labs to perform testing that was previously beyond their capabilities,” said Kirby, whose laboratory has extensive experience translating complex diagnostic methods into routine clinical practice, including leading early large-scale COVID-19 testing efforts in 2020. “This is a new tool in our fight against multidrug-resistant pathogens.”

Kirby’s team replaced the agar — the medium bacteria grow on in petri dishes — with an alternative called poloxamer. The key difference: agar is solid at room temperature whereas poloxamer is liquid. That one property streamlines the entire process for lab workers delivering gold-standard results while avoiding the technical pitfalls of the traditional method that can compromise test accuracy.

The elegant solution solves a longstanding problem. When a patient has a serious bacterial infection, physicians need to know which antibiotics will actually clear it, as soon as possible. That answer comes from the lab, where medical laboratory scientists find the lowest drug dose necessary to stop bacterial growth, a measurement called the minimum inhibitory concentration, or MIC. For most antibiotics, those tests run on automated machines. But for a handful of drugs — including some of the most important weapons against drug-resistant infections — the machines don’t give reliable results. The only trusted method is agar dilution: making a fresh batch of agar mixed with a precise concentration of antibiotic, pouring it into a plate, waiting for it to set, then repeating at the next concentration, and the next. The results are excellent, but hospitals’ limited time, space and staffing can add days to a process where hours count.

"Hospitals don’t need new instruments or commercial kits to use this approach,” said lead author Matthew T.J. Uy. “Labs can order the materials, validate the test locally as an in-house assay, and then begin using it for patient care.”

The timing gives this extra urgency. The FDA recently approved a new intravenous formulation of the antibiotic fosfomycin for the treatment of complicated urinary tract infections caused by drug-resistant bacteria. But, while hospitals can test whether some bacteria respond to fosfomycin, most clinical laboratories cannot easily perform the specialized testing needed to precisely measure how much of the drug is required to stop a patient’s infection. The reference method is agar dilution, and most hospitals can’t routinely perform it.

The poloxamer method solves that problem, bringing reliable fosfomycin testing within reach of standard hospital labs for the first time. And the approach could also work for other antibiotics where agar dilution is required, expanding hospitals’ diagnostic reach at a time when drug-resistant infections are on the rise.

Co-authors included Andrea Kirmaier and Lindsey M. Rudtner formerly of BIDMC; and Matthew T.J. Uy and Aidan Pine of Northeastern University and BIDMC.

This work was supported by a Novel Therapeutics Delivery Grant from the Massachusetts Life Science Center and a Carole Shapazian Research Co-op Fellowship from Northeastern University. The HP D300 digital dispenser was provided by TECAN (Morrisville, NC); TECAN had no role in study design, data collection, or interpretation.

About Beth Israel Deaconess Medical Center

Beth Israel Deaconess Medical Center is a leading academic medical center, where extraordinary care is supported by high-quality education and research. BIDMC is a teaching affiliate of Harvard Medical School, and consistently ranks as a national leader among independent hospitals in National Institutes of Health funding. BIDMC is the official hospital of the Boston Red Sox.

Beth Israel Deaconess Medical Center is a part of Beth Israel Lahey Health, a healthcare system that brings together academic medical centers and teaching hospitals, community and specialty hospitals, more than 4,700 physicians and 39,000 employees in a shared mission to expand access to great care and advance the science and practice of medicine through groundbreaking research and education.