Free-floating Carbon Nanotubes Can Promote “Nucleation” of Pathogenic Bacterial Aggregates

Carbon nanotubes (CNTs) are increasingly used in functional materials. As an unintended consequence, this is likely to increase CNTs in aqueous environments and in water treatment and delivery systems as a result of by-products of manufacture or by material degredation once in use. Aqueous systems are reservoirs for bacteria, including human pathogens that form biofilms. Although CNTs at sufficiently-high concentrations in designer materials are known to be anti-microbial, almost nothing is known about the interactions of bacteria with CNTs suspended in fluid at sub-lethal concentrations. Here, we investigate the impact of low concentrations of CNTs on the biofilm-forming human pathogen Pseudomonas aeruginosa. Using phase contrast and confocal microscopy and flow cytometry, we find that sublethal concentrations of CNTs promote the formation of aggregates of P. aeruginosa. Previous work by others has shown that P. aeruginosa aggregates have many of the harmful characteristics associated with biofilms, including increased virulence, antibiotic resistance, and resistance to the immune system. Thus, the presence of low levels of CNTs in open water and water supplies constitutes a potential threat to public health. We suggest possible countermeasures.