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Biomedicine

The Petri Dish Gets a Makeover

A nanopore membrane creates faster, surer cultures for everything from hospital diagnostics to water-quality checks.

A new type of diagnostic could let hospital laboratories identify the presence of dangerous bacteria up to five times faster than conventional methods. The test could reduce unnecessary antibiotic use and provide more reliable water-quality test results. The key to the process is a membrane with nanosized pores, which enable rapid growth and identification of live organisms.

The pore man’s solution: This nanopore membrane placed atop an agar plate allows nutrients and individual cells to move to the surface, growing bacterial microcolonies more quickly and enabling faster, more accurate diagnostics.

Current methods of identifying bacterial infections in hospitals seem almost antiquated: Swab, rub on petri dish filled with agar, and wait. Some bacteria can take 48 hours or more to grow into visible colonies. But the new technology, developed by Hubbard, Ohio-based Nanologix, speeds up the process. Bacteria, and potentially viruses, move through the pores of its membrane, and grow there. Then the membrane is plucked off the agar and placed on a staining plate.

“People knew for decades that microcolonies would be present in culture, but there was no way to transfer them or stain them in a way to make them visible,” says Nanologix CEO Bret Barnhizer. But the company’s technology—“bionanopore” membranes and “bionanofilters”—is sensitive enough to detect a single cell. And when the nanofilter is saturated with antibodies specific to a particular bacteria or virus, it can quickly indicate whether a particular offender is present.

The first test of the Nanologix system has been completed by a group of researchers at the University of Texas Health Sciences Center on a bacterium known as group B streptococcus. Also known as GBS, it can cause feeding, breathing, and other problems in a newborn baby if its mother is infected with it at the time of childbirth. Because of this, most pregnant women are tested for GBS about a month before their due date, with a culture test that yields results in two to three days. If the results are positive, antibiotics can eliminate the infection before the baby is born.

But if a woman arrives at a hospital in labor and has never been tested for GBS, she’s assessed for GBS risk and often given large doses of broad-spectrum antibiotics, just in case. Because the risk assessment basically consists of the physician’s best guess, some patients who need the antibiotics won’t get them, and some who don’t need them will.  

A study published online this month in the American Journal of Perinatology by the University of Texas researchers shows that the Nanologix test can yield reliable results in as few as four hours. It’s not fast enough to prevent antibiotic administration to untested women already in labor, but it’s fast enough to know whether their new babies should be monitored for signs of infection. “It would be great to have a faster-turnaround test,” says Kristin Brigger, a Houston private-practice obstetrician and gynecologist who was not involved in the research. “For patients in the academic setting, patients without good prenatal care and high risk of preterm labor, it would be really good.”

Other, more advanced technology already offers much faster turnaround than the Nanologix plates. Polymerase chain reaction machines can identify infection in as little as 30 minutes, fast enough for use between onset of labor and delivery. But such machines can be pricey, as can the individual tests, and the technology isn’t always available in community hospitals. In contrast, the Nanologix test kits cost between $5 and $10, just slightly more than the customary test, and can be done in any hospital lab. Barnhizer says the company also has developed kits that can detect E. coli, salmonella, listeria, and more; Nanologix plans to submit the first test (for GBS and other gram-positive bacteria) to the U.S. Food and Drug Administration later this year, with hopes for approval by the first quarter of 2012.

Nanologix is also working with the U.S. Environmental Protection Agency to develop kits that can be used during outbreaks for faster, more reliable detection of waterborne microorganisms such as E. coli and cryptosporidium. “It’s a really good technique, because it shortens a process of 12 to 18 hours to five or six, so we can get an answer about whether our target bacterium is there or not within a day,” says Gerard Stelma Jr., a senior microbiologist with the EPA in Cincinnati. Not only are currently available tests slow, he says, but their effectiveness also varies from day to day. “When I saw what they were doing, I thought this is the most novel new method I have seen in a number of years.” 

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