Antimicrobial Property of Halogenated Catechols

Abstract

Bacterial infection associated with multidrug resistance (MDR) bacteria is increasingly becoming a significant public health risk. Herein, we synthesized a series of halogenated dopamine methacrylamide (DMA), which contains a catechol side chain modified with either chloro-, bromo-, or iodo-functional group. Catechol is a widely used adhesive moiety for designing bioadhesives and coating. However, the intrinsic antimicrobial property of catechol has not been demonstrated before. These halogenated DMA were incorporated into hydrogels, copolymers, and coatings and exhibited more than 99% killing efficiencies against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. More importantly, hydrogel containing chlorinated DMA demonstrated broad-spectrum antimicrobial activities towards multiple MDR bacteria, which included methicillin resistant S. aureus (MRSA), vancomycin resistant enterococci (VRE), multi antibiotics resistant Pseudomonas aeruginosa (PAER), multi antibiotics resistant Acinetobacter baumannii (AB) and carbapenem resistant Klebsiella pneumoniae (CRKP). These hydrogels also demonstrated the ability to kill bacteria in a biofilm while exhibiting low cytotoxic. Based on molecular docking and molecular dynamics simulation, Cl-functionalized catechol can potentially inhibit bacterial fatty acid synthesis at the enoyl-acyl carrier protein reductase (FabI) step. The combination of moisture-resistant adhesive property, inherent antimicrobial property, and the versatility of incorporating halogenated DMA into different polymeric materials greatly enhanced the potential for using these monomers for designing multifunctional bioadhesives and coatings.

Keywords: antimicrobial; dopamine methacrylamide; halogenated catechol; multidrug resistant bacteria; mussel adhesive proteins.

Figure 1.

(a) Thermal initiated polymerization of halogenated DMA with AM and MBAA using AIBN to fabricate hydrogels. (b) FE-SEM of lyophilized AMDC. (c) Swelling ratios of hydrogels (g swollen hydrogel/g dried hydrogel) at pH 3, pH 7.4 and pH 9 after 48 h.

Figure 2.

CFU/mL for (a) S. aureus and (b) E. coli treated with hydrogels containing halogenated DMA and protected DMA-Cl after 8 h and 24 h (red circles indicate zero CFU/mL).

Figure 3.

FE-SEM images of (a) S. aureus biofilm grown for 24 h and (b) S. aureus biofilm treated with AMDC for 24 h. (c) Inset showing magnified morphology of deformed S. aureus and bacterial debris (white arrows). FE-SEM images of (d) E. coli biofilm grown for 24 h and (e) E. coli biofilm treated with AMDC for 24 h. (f) Inset showing magnified morphology of bacterial debris (white dashed circles).

Figure 4.

Fluorescence images of LIVE/DEAD bacterial staining assay of S. aureus (a and c) with AMM and (e and g) AMDC after 0 h and 24 h. Fluorescence images of LIVE/DEAD bacterial staining assay of E. coli (b and d) with AMM and (f and h) AMDC after 0 h and 24 h.

Figure 5.

(a) CFU/mL of MDR bacteria treated with AMM and AMDC after 24 h (red circles indicate zero CFU/mL). Morphology of PAER (b and c) and MRSA (d and e) biofilms visualized using FE-SEM after the biofilms were treated with AMM (b and d) and AMDC (c and e) for 24 h (White dashed circles indicate bacterial debris and deformation).

Figure 6.

(a) Cell viability of 3T3-E1 incubated with hydrogels for 24 h with extraction MTT assay. (b-f) Fluorescence images of LIVE/DEAD staining of 3T3-E1 cells seeded on hydrogels for 24 h.

Figure 7.

(a) Synthesis of copolymers P(AM-co-DMA) and P(AM-co-DMA-Cl). (b) Dip-coating the copolymers on the glass slide to render the surface antimicrobial. (c) FTIR spectra of uncoated glass slide and glass slides coated with P(AM₂-co-DMA₁) and P(AM₂-co-DMA-Cl₁). (d) CFU/mL of S. aureus and E. coli seeded on uncoated, P(AM₂-co-DMA₁) and P(AM₂-co-DMA-Cl₁) coated glass slides after 24 h.

Figure 8.

(a) The chemical structure of CDPPA. (b) The crystal structure of CDPPA /FabI/NAD⁺ ternary complex (FabI is colored green; CDPPA is colored orange; NAD⁺ is colored blue). (c) Binding models of CDPPA (orange) with the amino acids found at the active site of FabI and NAD⁺ (purple). (d) RMSD of the CDPPA/FabI/NAD⁺ ternary complex. (e) Number of hydrogen bonds formed in the CDPPA/FabI/NAD⁺ ternary complex. (f) Binding free energy contributions by amino acid residues and CDPPA.

Scheme 1.

(a) Chemical structures of polymerizable catechol-containing monomers. (b) Synthesis of DMA, DMA-Cl, DMA-Br and DMA-I through the modification of DMA with NCS, NBS, and ICI, respectively.