Bacterially derived carbon quantum dots for biofilm control

Bacterial infections are more challenging to treat by antibiotics when pathogens are attached to a surface and have grown into a biofilm. Carbon quantum dots can be applied as antimicrobials for prevention and treatment of biofilms. pH-responsive, 2,3-dimethylmaleic-anhydride modified carbon quantum dots (CDMMA-dots) reduced volumetric-bacterial-density within the acidic-environment of a biofilm for a non-extracellular polymeric substances (EPS)-producing Staphylococcus epidermidis strain, indicative for a more open structure. Such a structural disruption was not observed for an EPS-producing strain. Disrupted biofilms of the non-EPS-producing strain pre-exposed to CDMMA-dots were more amenable to vancomycin penetration and killing of their inhabitants. Carbon quantum dots derived from different bacterial strains possess similar physico-chemical properties with their source bacteria. After pyrolysis, protein and polysaccharide of bacteria could be maintained on carbon quantum dots, hydrocarbon-like bacterial components were transformed into new heterocyclic aromatic carbon structures, and nitrogen and phosphorus constituted heteroatoms in the carbon structure of carbon quantum dots. The physico-chemical similarities between carbon quantum dots and source bacteria stimulated the question whether carbon quantum dots derived from probiotic Bifidobacterium breve (B-C-dots) convey more favorable effects towards infection-control than carbon quantum dots derived from Escherichia coli (E-C-dots), an intestinal pathogen. Unlike E-C-dots, B-C-dots dispersed E. coli biofilms due to their higher release of reactive-oxygen-species as compared with E-C-dots. Moreover, pre-exposure of E. coli biofilms to B-C-dots enhanced ciprofloxacin efficacy in the control of intestinal E. coli infections. Therefore, synergistic application of antibacterial carbon quantum dots with existing antibiotics can be an effective strategy for infection control.