Abstract
This study aimed to address the significant problems of bacterial biofilms found in medical fields and many industries. It explores the potential of classic photoactive carbon dots (CDots), with 2,2′-(ethylenedioxy)bis (ethylamine) (EDA) for dot surface functionalization (thus, EDA-CDots) for their inhibitory effect on B. subtilis biofilm formation and the inactivation of B. subtilis cells within established biofilm. The EDA-CDots were synthesized by chemical functionalization of selected small carbon nanoparticles with EDA molecules in amidation reactions. The inhibitory efficacy of CDots with visible light against biofilm formation was dependent significantly on the time point when CDots were added; the earlier the CDots were added, the better the inhibitory effect on the biofilm formation. The evaluation of antibacterial action of light-activated EDA-CDots against planktonic B. subtilis cells versus the cells in biofilm indicate that CDots are highly effective for inactivating planktonic cells but barely inactivate cells in established biofilms. However, when coupling with chelating agents (e.g., EDTA) to target the biofilm architecture by breaking or weakening the EPS protection, much enhanced photoinactivation of biofilm-associated cells by CDots was achieved. The study demonstrates the potential of CDots to prevent the initiation of biofilm formation and to inhibit biofilm growth at an early stage. Strategic combination treatment could enhance the effectiveness of photoinactivation by CDots to biofilm-associated cells.
Highlights
Bacterial biofilms represent a significant problem in the medical field
The results show that, even with a higher carbon dots (CDots) concentration of 20 or 30 μg/ml, the CDots must be added within the first 2 h after the initiation of biofilm growth to achieve 100% or nearly 100% inhibitory effect on the final biofilm formation detected at 48 h
The results show that the combination of ethylenediaminetetraacetic acid (EDTA) and EDA-CDots/visible light treatments was highly effective for the inactivation of biofilm-associated B. subtilis cells with more than six log viable cell reduction by the combination of 5 mM EDTA and 30 μg/ml EDA-CDots (Figure 5)
Summary
Bacterial biofilms represent a significant problem in the medical field. Biofilms colonize and damage a wide variety of medical implants and devices, but they cause a majority of bacterial infections in humans (Singh et al, 2018) with an estimated up to 80% of all human bacterial infections being associated with biofilms (Römling and Balsalobre, 2012). The mechanical networks of EPS in mature biofilms protect the microorganisms; retain water, organic compounds, inorganic ions, and extracellular enzymes; enable redox activity; and facilitate horizontal gene transfer (Flemming and Wingender, 2010; Marvasi et al, 2010; Sretenovic et al, 2017). Such structure and lifestyle of a biofilm afford it strong capability to withstand hostile environmental conditions and make it much more resistant to antibiotics, disinfection, and/ or sanitization when compared with their planktonic bacteria counterparts (Mah and O’Toole, 2001; Bridier et al, 2015). In the work reported here, the newly developed carbon “quantum” dots or carbon dots (CDots) (Sun et al, 2006; Sun, 2020), coupled with visible light are explored with significant success in both prevention and eradication efforts
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