Chip technology could cut the wait for test results on clinical samples, say US scientists. A team at the University of Chicago has developed a method to detect bacteria in blood plasma samples and simultaneously screen their response to antibiotics.

Converting a weak bacterial solution into droplets means it can be screened against several different antibiotic

The group's technique works by mixing a sample with a dye that fluoresces in the presence of bacteria; the mixture is then converted into droplets inside a microfluidic chip. If the sample contains bacteria some of the droplets will contain a single bacterium and fluoresce. Because of the very small droplet size, the occupied droplets will have a high bacterial density, removing the need to incubate samples to increase their concentration before detection. 

The team was able to use the method to detect the MRSA (methicillin-resistant Staphylococcus aureus) 'superbug', so-called because of its resistance to several antibiotics. They were also able to find potential treatments for MRSA infections by treating an array of the droplets with different antibiotics and looking at the change in fluorescence. 

Rustem Ismagilov, who led the team, explains that his motivation was rooted in improving medical diagnostic tests. Traditional methods of diagnosing bacterial infections rely on time-consuming sample incubations or amplifying the bacterial DNA which, while faster, cannot be used to look at antibiotic response. 'Our technique can potentially provide access to new types of diagnostic tests for bacterial infections and simultaneously identify a treatment regime to provide same-day test results,' says Ismagilov.

But not only that, 'it could also provide a simple and inexpensive solution to testing for bacteria in other fields where contamination by bacteria is a concern, including the food industry and water management,' Ismagilov adds.

Samuel Sia, an expert in lab-on-a-chip diagnostic devices at Columbia University, New York, US, is enthusiastic about the research. 'The finding that confining a single bacterium to a small volume can decrease detection time is a striking demonstration of the advantages of microfluidics,' he says. Whilst he explains that considerable development and clinical testing will be needed before such an assay could be used for real-world diagnostics, he adds that 'the experimental design is very clever, and the results convincing.'

Kathleen Too