In equine practice, it is common to perform bacterial culture and sensitivity testing on bodily samples to determine the most efficacious treatment program that has the least likelihood of encouraging antibiotic resistance. The use of rapid antimicrobial susceptibility tests (AST) is a relatively inexpensive and rapid means of discerning which antimicrobial agents might be most effective in treatment. Studies have examined monitoring of bacterial nanomotion via atomic force microscopy as one means of achieving a rapid AST [ Villab, MI.; Rossetti, E.; Bonvallat, A.; et al. Simple optical nanomotion method for single-bacterium viability and antibiotic response testing. PNAS April 2023, vol. 120, # 18; doi: 10.1073/pnas.2221284120].
In a recent study, the authors noted that the only requirements to conduct this test are “a very basic microfluidic analysis chamber and an optical microscope equipped with a camera or mobile phone.” No bacterial stains, markers or attachment of the microorganisms are necessary to conduct the testing. It can be used on motile, nonmotile, gram-positive and gram-negative bacteria. Dedicated software developed for this purpose achieves reliable antibiotic susceptibility testing with the above-mentioned equipment.
Nanometric oscillations of a bacterium can determine life or death status, i.e. a signature of life. The procedure is referred to as optical nanomotion detection (ONMD) and is sensitive enough to evaluate a single cell. Testing can be done over a span of 1-2 hours. In addition to monitoring life-death transitions when exposed to various chemicals/antimicrobial agents, it is possible to detect bacterial metabolic variations induced by different nutrient concentrations.
The authors concluded: “The technique is rapid, extremely simple to set up, possesses a single-cell sensitivity, is attachment- and label-free, and significantly faster and cheaper than other existing fast AST methods. Importantly, it is independent of the bacterial replication rate, the structure of their cell wall, or motility. This technique allowed us to study bacteria viability and assess nanomotion under different nutrient and antibiotic conditions.”
