Lab-on-a-stick tests antibiotic resistance

ENGINEERS in the UK have developed a ‘lab-on-a-stick’ which they say can cheaply and quickly identify bacterial resistance to antibiotics, blood type, and distinguish between bacteria species.

Loughborough University chemical engineering lecturer Nuno Reis and University of Reading professor of biomedical technology Al Edwards led the research to develop the lab-on-a-stick, which works without the need for any power and requires no laboratory. Antibiotic-resistant bacteria are becoming increasingly common, and treating such infections can be difficult. Currently, testing samples to determine antibiotic resistance can take several days, as the bacteria must be cultured and tested with the drug, but the-lab-on-a-stick can work much faster. Rapid blood-typing tests possible outside of a lab would also be extremely useful, for example in emergencies, while bacterial identification can be a long and laborious process.

The lab-on-a-stick works on the same principle as a conventional dipstick, for example like that used to detect pregnancy, but is made up of ten microfluidic capillaries, each about the width of a human hair, arranged in a strip. The inside of the fluoropolymer capillary walls are coated with a hydrophilic layer of polyvinyl alcohol, and then the desired reagent. When the strip is placed into a liquid, it is drawn up into the tubes by capillary action.

To test for antibiotic resistance, Reis and Edwards use different concentrations of antibiotic ranging from 0-100 μg/ml as the desired reagent, and disperse bacterial cells in resazurin growth indicator medium, which changes colour from blue to pink and ultimately white, in response to aerobic respiration. The strip is placed in the growth medium containing the cells to draw up samples, then incubated overnight. At ineffective concentrations of antibiotic, the capillary changes colour as the bacterial cells can still grow and respire. Where the antibiotic is effective, the bacterial cells do not grow and the capillary remains blue. The researchers are working on reducing the incubation time to a couple of hours.

To determine blood type, the researchers coated the capillaries with the same antibodies used in conventional bloodtyping, which react to the presence of certain proteins on the blood cell wall – either A, B, or Rhesus factor, with some capillaries left as negative controls. The researchers observed rapid blood cell clumping in the capillary with a positive reaction, eg type A blood clumped in the capillaries with the antibodies for type A blood cells, while the blood rose uniformly up the other capillaries.

Reis and Edwards also developed strips which could distinguish between different species of bacteria, by using different sugars as the reagent. Different bacterial species can only metabolise certain types of sugar. The bacteria to be tested was suspended in a growth medium contain phenol red, which turns yellow in the acidic environment created when bacteria metabolise sugar. By looking at which capillaries had turned yellow, and therefore which sugars that particular species had been able to metabolise, the researchers could determine which species it was.

“This is the latest demonstration of our exciting new technology called microcapillary film. Many researchers across the world have shown how miniaturising lab tests can speed them up using microfluidic lab-on-a-chip devices. But these are too expensive to be useful outside the laboratory. What we have done is to develop a low cost way of making thousands of miniature test tubes, so that we can use them for many important applications. Lab-on-a-stick shows yet again how versatile these microscopic test tubes are,” says Edwards.

Lab on a Chip DOI: 10.1039/C6LC00332J