Editors' ChoiceNanotechnology

Bacterial Vibrations

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Science Translational Medicine  31 Jul 2013:
Vol. 5, Issue 196, pp. 196ec126
DOI: 10.1126/scitranslmed.3007046

Antibiotic treatment becomes futile when bacteria evolve to evade it. Timely identification of antibiotic resistance is therefore important to curb a bacterial infection. Conventional methods to screen for bacterial resistance to antibiotics typically rely on time-consuming assays that measure growth patterns. Longo et al. offer a solution to this problem by using atomic force microscopy (AFM) to detect small changes in the movements of bacteria, which appear to reflect their antibiotic resistance.

Bacteria display subnanometer-scale movements, possibly as a result of their metabolic activity and cell membrane dynamics. Not visible to the eye, these tiny vibrations are easily detectable with AFM, which comprises a miniature cantilever and an optical sensor to register the fluctuations of the cantilever. In this setup, the authors found that clinically relevant bacterial samples—including Escherichia coli (both ampicillin-resistant and -sensitive strains) and Staphylococcus aureus obtained from culture—adhered to a chemically functionalized cantilever, and a laser-photodetector pair monitored the mechanical fluctuations of moving bacteria. When the bacteria were exposed to their nourishing media, the fluctuations picked up within minutes. Supplementing the media with glucose further augmented the fluctuations, hinting at a possible relationship between metabolic activity and nanoscale bacterial movements. Conversely, ampicillin or kanamycin treatment diminished or halted the fluctuations, regardless of whether or not the specific bacterial strain was resistant. The fluctuations resumed for resistant bacteria exposed to certain antibiotics.

Because this screening method reduced the time to quantify antibiotic resistance—in part by not relying on bacterial growth assays—it has the potential to affect the determination of antibiotic resistance of slow-growing bacteria, such as the clinically relevant Mycobacteria. AFM systems are, however, very sensitive to mechanical perturbations and require skilled users; hence, the screening system will need to be automated for ease of use in a clinical setting.

G. Longo et al., Rapid detection of bacterial resistance to antibiotics using AFM cantilevers as nanomechanical sensors. Nat. Nanotechnol., published online 30 June 2013 (10.1038/nnano.2013.120). [Abstract]

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