Fast test reveals drug-resistant bacteria

A new test quickly reveals whether bacteria are vulnerable to antibiotics, researchers report in the Dec. 17 Science Translational Medicine. They used time-lapse photography to see whether individual bacteria cells divide or change shape.

To choose the right antibiotics to treat a patient with a bacterial infection, doctors must determine which drugs the bacteria are sensitive to. Using traditional tests, doctors expose a sample of bacteria to antibiotics and wait 16 to 20 hours. If the cell culture darkens, it is full of bacteria dividing, uninhibited by the drug.

In practice, doctors sometimes cannot wait and must guess which antibiotic to use, even though prescribing the wrong drug can contribute to antibiotic resistance.

Researchers in South Korea gauged how bacteria respond to antibiotics using a plastic chip with many little wells, each holding bacterial cells immobile in a thick gel. The researchers pumped in antibiotics and took time-lapse images. The new test, which takes four hours, shows individual cells dividing and changing shape.

Some bacteria swell or grow filaments in response to antibiotics. The changes can look like dividing bacteria, when in fact the antibiotics have damaged the cells.

“If you look at the shape change, you can be a lot more accurate,” says study coauthor Sunghoon Kwon, a bioengineer at Seoul National University.

Kwon and his colleagues tested the method on infectious bacteria including Staphylococcus aureus and E. coli. The test met the Food and Drug Administration standards for accuracy. Kwon and colleagues now want to apply the test to slowly dividing bacteria like tuberculosis. Conventional tests take months; Kwon hopes to cut that time down to one week.