Naked-eye detection of antibiotic resistance gene sul1 based on aggregation of magnetic nanoparticles and DNA amplification products

The continued spread of antimicrobial resistance is a global problem. In fact, the WHO has declared antimicrobial resistance one of the top 10 global public health threats facing humanity. Molecular methods offer a faster means of characterizing resistant strains than phenotypic drug susceptibility testing. We have developed a molecular detection method that generates visible aggregates from DNA amplified products and functionalized magnetic nanoparticles. The amplification and detection procedure take less than 2 h. In this study we also investigated the factors behind the aggregation and confirmed that the size of the padlock probe is a relevant parameter for the amplification efficiency. We compared a 92 and a 69 nt long padlock probe and found the latter to perform over 4 times better than the 92 nt padlock probe. This effect was related to a higher quantity of amplification products produced by the shorter padlock probe. Consequently, the quantity of amplified DNA products affects the aggregation in a positive way, and thanks to it, a better assay sensitivity was achieved. Finally, using our developed method, we could detect as little as 1 amol of the antibiotic-resistance gene sul1 from a sample containing a multiresistance plasmid. We were also able to quantify the amount of plasmid DNA through absorbance spectroscopy and AC susceptometry. The presented results form the foundation of future development of an ultrasensitive and cheap detection approach that could be used in point of care settings.