Measuring pathogen susceptibility to antibiotics

In just 30 minutes, a new method can determine if the bacteria in a person’s urine sample are vulnerable to a certain antibiotic (Sci. Transl. Med. 2017, DOI: 10.1126/scitranslmed.aal3693). Such a test could help doctors better manage antibiotic use when treating urinary tract infections (UTIs) by allowing them to reserve valuable, potent drugs for when other drugs will not work. In the new method, Rustem F. Ismagilov of California Institute of Technology and colleagues incubate bacteria in a urine sample either with or without an antibiotic of choice for 15 minutes. By comparing the bacterial DNA levels between the two conditions, the researchers can determine if the infectious strain is susceptible to the drug. To detect such small differences in DNA levels, the team uses an optimized version of loop-mediated isothermal amplification on a microfluidic chip to count the copies of a certain piece of DNA from Escherichia coli—the most common bacterial culprit in UTIs. The team tested the method on 54 patient samples and found that, 94% of the time, the results agreed with those from the standard culture-based method for determining antibiotic susceptibility, which takes days to yield results. Joseph C. Liao, a urologist at Stanford University School of Medicine, thinks performing such a measurement in 30 minutes is a technical tour de force. He’s interested in seeing the team apply the method to a wider range of microbes and drugs.