Klebsiella pneumoniae growing in the microfluidic chip imaged in phase contrast. The bacteria are 0.003 mm long and divide every 30 minutes. [Özden Baltekina et al./Uppsala University]

Scientists at Uppsala University report the development of a novel technique that can quickly determine whether infection-causing bacteria are resistant or susceptible to antibiotics. Their study (“Antibiotic Susceptibility Testing in Less Than 30 Min Using Direct Single-Cell Imaging”) is published in Proceedings of the National Academy of Sciences

“…we investigate if it is possible to develop a point-of-care susceptibility test for urinary tract infection, a disease that 100 million women suffer from annually and that exhibits widespread antibiotic resistance,” write the investigators. “We capture bacterial cells directly from samples with low bacterial counts (104 cfu/mL) using a custom-designed microfluidic chip and monitor their individual growth rates using microscopy.”

(A) Overall workflow for fast antibiotic susceptibility test (AST). (B) Individual cells are sucked into the cell channels where they get stuck at the 300-nm constriction at the end (inset). (C1) One row of 2000 cell channels are treated with an antibiotic and the other row is used as a reference. (C2) Growth in one individual cell channel without antibiotic (left) and one with antibiotic (right ) monitored over time (x axis) as observed with phase-contrast microscopy. (C3) Length extension over time as determined for cells in 1600 individual cell channels without antibiotic (left) and with antibiotic (right). (C4) Average growth rates for the bacteria in C3 together with 99.9% SEM and population standard deviation. (D) The average growth rate and 99.9% SEM for susceptible bacteria exposed to one of of nine different antibiotics (colors), normalized to the growth rate in the nontreated reference channels. Only data from one typical references channel is displayed (gray). Dots indicate when the growth rate has dropped below untreated reference with 99.9% probability. [Johan Elf/Uppsala University]

“We find that it is possible to detect changes in growth rate in response to each of nine antibiotics that are used to treat urinary tract infections in minutes. In a test of 49 clinical uropathogenic Escherichia coli (UPEC) isolates, all were correctly classified as susceptible or resistant to ciprofloxacin in less than 10 min. The total time for antibiotic susceptibility testing, from loading of sample to diagnostic readout, is less than 30 min, which allows the development of a point-of-care test that can guide correct treatment of urinary tract infection.”

One important contributory factor in the development of resistance is the incorrect use of antibiotics for treatment. Reliable methods to quickly and easily identify bacterial resistance patterns (antibiotic susceptibility testing, or AST) and provide the proper treatment from the start, i.e., right from the doctor's appointment, are a solution to the problem. This has not been possible because existing antibiotic resistance tests take too long, according to the scientists.

“We've developed a new method that allows determination of bacterial resistance patterns in urinary tract infections in 10 to 30 minutes. By comparison, the resistance determination currently in use requires one to two days. The rapid test is based on a new plastic microfluidic chip where the bacteria are trapped and methods for analyzing bacterial growth at single-cell level,” says Ph.D. student Özden Baltekin, who performed most of the experimental work.

The “fASTest” method relies on optical and analytical approaches developed to study the behavior of individual bacteria. Monitoring whether individual bacteria grow in the presence of antibiotics (i.e., are resistant) or not (are susceptible) reveals their resistance or susceptibility within a few minutes.

The detection method is now being developed by an Uppsala company. Based on this research Astrego Diagnostics is developing an automated test for urinary tract infections which it expects to have on the market in a few years.

“We believe the method is usable for other types of infection, such as blood infections where prompt, correct choice of antibiotic is critical to the patient,” says Dan Andersson, Ph.D., professor and one of the researchers involved in the study.

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