Antibiotic Susceptibility Testing Using Simple Microscope and Smartphone


Researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have developed a simple and rapid technique to assess the antibiotic susceptibility of bacterial samples. At present, this is time consuming and inefficient, often leading to disease progression while patients await lab results. This new approach involves a simple optical microscope and a video camera, such as those commonly found in smartphones. The bacteria are loaded into a simple microfluidic device, and then exposed to a given antibiotic. The bacterial cells are then observed through the microscope and video footage of the nanoscale vibrations that are a hallmark of living bacteria is obtained. Once the bacteria stop vibrating, you can assume that they are dead, revealing their susceptibility to the antibiotic drug.

A. Setup to conduct Optical Nanomotion Detection based antibiotic susceptibility test: a low cost optical microscope and a mobile phone are enough. B. Optical image of E. coli bacteria. C. Same field of view as B in false colors that highlight bacterial displacements; Red: high amplitude motion; Blue: no displacement. Credit: Ines Villalba (EPFL)

Antibiotic resistance is becoming a growing issue which costs health services significant resources to fight and manage. It also underlies many patient deaths around the world every year, and this is set to increase as bacteria continue to develop resistance. Determining whether the bacteria causing an infection in a patient are resistant to particular antibiotics is important. Administering the wrong antibiotic will waste precious time in which to get the infection under control, so finding the best drug to use as quickly as possible is key.

However, current lab techniques are typically not very fast, and often involve culturing the bacteria until there are enough to perform the susceptibility tests, which involve exposing bacterial samples to a panel of drugs and then observing whether the bacterial cells die or not. There are also methods that involve genetic testing to determine if the bacteria have genes that confer resistance against particular drugs. These methods often take over 24 hours, which can make the difference between the infection progressing or not, and may also require expensive and bulky lab equipment and highly trained technicians to do everything right.

To address this, these researchers have developed a relatively simple technique that does not require specialized equipment. Most importantly, it is very fast, taking just a few hours. “We have developed a technique in our laboratories that allows us to obtain an antibiogram within 2-4 hours — instead of the current 24 hours for the most common germs and one month for tuberculosis,” said Sandor Kasas, a researcher involved in the study. “Our technique is not only faster but also simpler and much cheaper than all those existing now,” added Ronnie Willaert, a second researcher who contributed to the project.

The method involves adding the bacterial sample to a simple microfluidic device and then introducing a sample of the antibiotic to be tested. After a short incubation, the bacteria can be viewed and videoed using a simple optical microscope and a smartphone camera. Live bacteria demonstrate nanoscale vibrations, which can be viewed through the microscope. If the bacteria are dead, then they stop vibrating, which can also be observed through the microscope. These cell movements are monitored by the system, revealing the antibiotic susceptibility of the bacterial sample in very little time.  

Study in PNAS: Simple optical nanomotion method for single-bacterium viability and antibiotic response testing


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