Researchers at the University of Connecticut have developed a highly sensitive imaging sensor that can rapidly and accurately monitor bacterial growth. The technique involves shining laser light through a bacterial sample and taking images at multiple orientations, before reconstructing the diffracted light patterns, to produce a 3D image of the bacterial colony. These 3D images provide significant detail about the growth and characteristics of bacteria, and could be very helpful in rapidly identifying which antibiotics are most effective at killing them.
Determining antibiotic susceptibility is a laborious process. A bacterial sample that has been isolated from a patient will typically be cultured on a nutrient medium, such as agar. Once there are enough bacteria present, which may take several days, lab technicians will then start exposing them to different antibiotics. Only then can they assess whether the bacteria are susceptible to certain drugs.
This can be too long to wait for someone with a dangerous infection. As such, developing more rapid antibiotic susceptibility tests is an active area of research. This latest technique relies on imaging the bacteria in 3D to provide more information than conventional 2D images. For instance, if a bacterial colony was growing upwards, but not outwards, conventional imaging techniques would not readily reveal this, meaning that lab technicians would assume that the colony was not growing at all.
Conversely, this new technique will reveal such growth, providing a more accurate overview of bacterial viability and proliferation. “For the 3D model it’s an accurate measure of how fast the bacteria grow,” said Guoan Zheng, one of the developers of the new technology, in a University of Connecticut press release. “If you just use the 2D model, it simply just doesn’t give you the accurate measure to quantify that growth.”
His team’s system consists of a laser to illuminate the bacterial sample, a sensor coated with microbeads that scatter the light, and a temperature-control component that allows the researchers to keep the bacteria at the perfect temperature for culturing. The entire system should fit within a conventional incubator.
After imaging the sample at different positions, the researchers reconstruct the resulting diffracted light patterns using an imaging technique called ptychography. This results in 3D images that are more informative for the researchers in terms of bacterial growth. The technique is also rapid, allowing the University of Connecticut team to image the bacteria over a 15-second period, essentially tracking their growth in real time.
Here’s a video from Guoan Zheng showing the tracking of bacterial growth at 15-second intervals and a centimeter-scale field of view using the new sensor. Images shown here are the recovered phase profiles of a micro-colony:
Study in journal Biosensors and Bioelectronics: Ptychographic sensor for large-scale lensless microbial monitoring with high spatiotemporal resolution