Enhanced antibacterial activity of the gentamicin against multidrug-resistant strains when complexed with Canavalia ensiformis lectin

Glucose-Binding Dioclea bicolor Lectin (DBL): Purification, Characterization, Structural Analysis, and Antibacterial Properties

In this study, we purified a lectin isolated from the seeds of Dioclea bicolor (DBL) via affinity purification. Electrophoresis analysis revealed that DBL had three bands, α, β, and γ chains, with molecular masses of approximately 29, 14, and 12 kDa, respectively. Gel filtration chromatography revealed that the native form of DBL had a molecular mass of approximately 100 kDa, indicating that it is a tetramer. Interestingly, DBL-induced hemagglutination was inhibited by several glucosides, mannosides, ampicillin, and tetracycline with minimum inhibitory concentration (MIC) values of 1.56-50 mM. Analysis of the complete amino acid sequence of DBL revealed the presence of 237 amino acids with high similarity to other Diocleinae lectins. Circular dichroism showed the prominent β-sheet secondary structure of DBL. Furthermore, DBL structure prediction revealed a Discrete Optimized Protein Energy (DOPE) score of -26,642.69141/Normalized DOPE score of -1.84041. The DBL monomer was found to consist a β-sandwich based on its 3D structure. Molecular docking showed the interactions between DBL and α-D-glucose, N-acetyl-D-glucosamine, α-D-mannose, α-methyl-D-mannoside, ampicillin, and tetracycline. In addition, DBL showed antimicrobial activity with an MIC of 125 μg/mL and exerted synergistic effects in combination with ampicillin and tetracycline (fractional inhibitory concentration index ≤ 0.5). Additionally, DBL significantly inhibited biofilm formation and showed no toxicity in murine fibroblasts (p < 0.05). These results suggest that DBL exhibits antimicrobial activity and works synergistically with antibiotics.

Structural characterization of a galectin from the marine sponge Aplysina lactuca (ALL) with synergistic effects when associated with antibiotics against bacteria

Lectins presents the ability to interact with glycans and trigger varied responses, including the inhibition of the development of various pathogens. Structural studies of these proteins are essential to better understand their functions. In marine sponges, so far only a few lectins have their primary structures completely determined. Thus, the objective of this work was to structurally characterize and evaluate antibacterial potential, in association with different antibiotics, of the lectin isolated from the marine sponge Aplysina lactuta (ALL). ALL is a homotetramer of 60 kDa formed by four 15 kDa-subunits. The lectin showed affinity only for the glycoproteins fetuin, asialofetuin, mucin type III, and bovine submaxillary mucin type I. The complete amino acid sequences of two isoforms of ALL, named ALL-a and ALL-b, were determined by a combination of Edman degradation and overlapped peptides sequenced by tandem mass spectrometry. ALL-a and ALL-b have 144 amino acids with molecular masses of 15,736 Da and 15,985 Da, respectively. Both structures contain conserved residues typical of the galectin family. ALL is a protein with antibacterial potential, when in association with ampicillin and oxacillin the lectin potentiates its antibiotic effect, included Methicillin-resistant Staphylococcus strains. Thus, ALL shows to be a molecule with potential for the development of new antibacterial drugs.

Isolation of lectin from Musa acuminata for its antibiofilm potential against Methicillin-resistant Staphylococcus aureus and its synergistic effect with Enterococcus species

Methicillin resistant Staphylococcus aureus (MRSA) is an emerging pathogen posing a considerable burden on the healthcare system due to its involvement in skin and soft tissue infections (SSTIs). Lectins are carbohydrate binding proteins found ubiquitously in animals, plants and microorganisms. Extraction and isolation of proteins from Musa acuminata were performed by using Affinity chromatography with Sephadex G 75 to determine antibiofilm activity against MRSA. Enterococcus strains obtained from dairy products, beans and vegetables were also screened for its potential to inhibit growth and biofilm formation of MRSA by using 96 well microtiter plates. Synergistic effect of cell free supernatant of Enterococcus with proteins from ripe banana were also tested. BanLec was successfully isolated and appeared as 15 KDa band after SDS-PAGE (15%) while multiple bands of unbound protein fractions were observed. The unbound fractions showed inhibition of planktonic cells and biofilm but BanLec exhibited no significant effect. The CFS of Enterococcus faecium (LCM002), Enterococcus lactis (LCM003) and Enterococcus durans (LCM004 and LCM005) displayed antagonistic effects against pathogen. The synergistic effect of CFS from E. lactis (LCM003) and unbound proteins showed inhibition of biofilm and pathogenic growth. This study demonstrates the use of Enterococcus species and plant proteins against pathogens and results suggested that it can inhibit the growth of resistant strains of Staphylococcus aureus and their synergistic effect has opened new ways to tackle emerging resistance. Furthermore, after assessment of Enterococcus as probiotics, this could be used in food industries as well as in treatment of severe skin infections.

Dioclea violacea lectin increases the effect of neomycin against multidrug-resistant strains and promotes the purification of the antibiotic in immobilized lectin column

DVL is a Man/Glc-binding lectin from Dioclea violacea seeds that has the ability to interact with the antibiotic gentamicin. The present work aimed to evaluate whether the DVL has the ability to interact with neomycin via CRD and to examine the ability of this lectin to modulate the antibiotic effect of neomycin against multidrug-resistant strains (MDR). The hemagglutinating activity test revealed that neomycin inhibited the hemagglutinating activity of DVL with a minimum inhibitory concentration of 50 mM, indicating that the antibiotic interacts with DVL via the carbohydrate recognition domain (CRD). DVL immobilized on cyanogen bromide-activated Sepharose® 4B bound 41 % of the total neomycin applied to the column, indicating that the DVL-neomycin interaction is efficient for purification processes. Furthermore, the minimum inhibitory concentrations (MIC) obtained for DVL against all strains studied were not clinically relevant. However, when DVL was combined with neomycin, a significant increase in antibiotic activity was observed against S. aureus and P. aeruginosa. These results demonstrate the first report of lectin-neomycin interaction, indicating that immobilized DVL has the potential to isolate neomycin by affinity chromatography. Moreover, DVL increased the antibiotic activity of neomycin against MDR, suggesting that it is a potent adjuvant in the treatment of infectious diseases.

Plant Lectins: A Review on their Biotechnological Potential Toward Human Pathogens

The indiscriminate use of antibiotics is associated with the appearance of bacterial resistance. In light of this, plant-based products treating infections are considered potential alternatives. Lectins are a group of proteins widely distributed in nature, capable of reversibly binding carbohydrates. Lectins can bind to the surface of pathogens and cause damage to their structure, thus preventing host infection. The antimicrobial activity of plant lectins results from their interaction with carbohydrates present in the bacterial cell wall and fungal membrane. The data about lectins as modulating agents of antibiotic activity, potentiates the effect of antibiotics without triggering microbial resistance. In addition, lectins play an essential role in the defense against fungi, reducing their infectivity and pathogenicity. Little is known about the antiviral activity of plant lectins. However, their effectiveness against retroviruses and parainfluenza is reported in the literature. Some authors still consider mannose/ glucose/N-Acetylglucosamine binding lectins as potent antiviral agents against coronavirus, suggesting that these lectins may have inhibitory activity against SARS-CoV-2. Thus, it was found that plant lectins are an alternative for producing new antimicrobial drugs, but further studies still need to decipher some mechanisms of action.

Plant lectins: A new antimicrobial frontier

Pathogenic bacteria, viruses, fungi, parasites, and other microbes constantly change to ensure survival. Several pathogens have adopted strict and intricate strategies to fight medical treatments. Many drugs, frequently prescribed to treat these pathogens, are becoming obsolete and ineffective. Because pathogens have gained the capacity to tolerate or resist medications targeted at them, hence the term antimicrobial resistance (AMR), in that regard, many natural compounds have been routinely used as new antimicrobial agents to treat infections. Thus, plant lectins, the carbohydrate-binding proteins, have been targeted as promising drug candidates. This article reviewed more than 150 published papers on plant lectins with promising antibacterial and antifungal properties. We have also demonstrated how some plant lectins could express a synergistic action as adjuvants to boost the efficacy of obsolete or abandoned antimicrobial drugs. Emphasis has also been given to their plausible mechanism of action. The study further reports on the immunomodulatory effect of plant lectins and how they boost the immune system to curb or prevent infection.

Potential Application of Combined Therapy with Lectins as a Therapeutic Strategy for the Treatment of Bacterial Infections

Antibiotic monotherapy may become obsolete mainly due to the continuous emergence of resistance to available antimicrobials, which represents a major uncertainty to human health. Taking into account that natural products have been an inexhaustible source of new compounds with clinical application, lectins are certainly one of the most versatile groups of proteins used in biological processes, emerging as a promising alternative for therapy. The ability of lectins to recognize carbohydrates present on the cell surface allowed for the discovery of a wide range of activities. Currently the number of antimicrobials in research and development does not match the rate at which resistance mechanisms emerge to an effective antibiotic monotherapy. A promising therapeutic alternative is the combined therapy of antibiotics with lectins to enhance its spectrum of action, minimize adverse effects, and reduce resistance to treatments. Thus, this review provides an update on the experimental application of antibiotic therapies based on the synergic combination with lectins to treat infections specifically caused by multidrug-resistant and biofilm-producing Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. We also briefly discuss current strategies involving the modulation of the gut microbiota, its implications for antimicrobial resistance, and highlight the potential of lectins to modulate the host immune response against oxidative stress.