In light of rising antimicrobial resistance, scientists have turned to metallic compounds to fight bacterial infections. By sculpting metallic compounds of silver, copper, and zinc into tiny spikes called nanowires, one can essentially stab the bacteria and and prevent them from growing. The design of nanowires was originally inspired by nature: cicadas and dragonflies have similar structures on their wings, helping them curb the spread of harmful bacteria.
Not all bacteria easily fall prey to nanowires, though. A recent study has found that, among Gram negative bacteria, antibiotic resistant and susceptible strains have different mechanical properties. The researchers used atomic force microscopy to determine the stiffness of a host of different types of bacteria. Across the board, they saw that antibiotic-susceptible bacteria were “tougher” and stiffer, able to withstand more poking and prodding. Antibiotic-resistant bacteria, on the other hand, were “softer" and thus more likely to be impaled by nanowires. But what is the reason for this difference?
Beta-lactams, the most widely used class of antibiotics, kill bacteria by preventing them from adding peptidoglycan, a key component for mechanical strength, to their cell walls. When the scientists looked at how strains resistant or susceptible to antibiotics made their cell walls, they found that the softer resistant strains make and use less peptidoglycan. This likely stems from generations of exposure to sub-lethal concentrations of beta-lactams, making the cell walls of antibiotic-resistant strains progressively thinner and softer.
Based on theoretical analysis, the researchers then crafted some nickel-cobalt-based nanowires of different tip diameters. They found that a tip diameter of 5 nanometers — about 20,000 times thinner than a human hair — penetrated the soft antibiotic-resistant bacteria best, but had little effect on the tough, antibiotic-susceptible bacteria. This is a promising development toward a potential solution to the pesky problem of antimicrobial resistance.