Synergy of the Bacteriocin AS-48 and Antibiotics against Uropathogenic Enterococci

Synergistic Activity of Ingulados Bacteria with Antibiotics against Multidrug-Resistant Pathogens

Antimicrobial resistance is a critical challenge due to the overuse of conventional antimicrobials, and alternative solutions are urgently needed. This study investigates the efficacy of compounds derived from lactic acid bacteria (LAB) fermentation combined with antibiotics against multidrug-resistant pathogens isolated from clinical cases in a hospital setting. Strains of Escherichia coli, Klebsiella pneumoniae, and Enterococcus faecium and faecalis were isolated and selected from blood, respiratory, and urine samples. They were tested against the fermentation products from the Ingulados LAB collection (BAL5, BAL6, BAL8, BAL13, and BAL16), recognized for their antimicrobial efficacy against veterinary pathogens. The activity against multidrug-resistant (MDR) pathogens was evaluated initially, followed by synergy tests using checkerboard assays and subsequent analysis. Bioinformatic assessments and supernatant treatments were performed to characterize the nature of the compounds responsible for the antimicrobial activity. Notably, BAL16 exhibited significant growth inhibition against multidrug-resistant E. faecium. Synergy tests highlighted its combined activity with tetracycline through FICI and surface analysis and bioinformatic analysis unveiled the protein fraction containing bacteriocins as the underlying mechanism. This study highlights BAL16 fermentation products potential as valuable antimicrobial agents against MDR E. faecium infections, attributed to bacteriocins. Further in-depth studies are necessary for complete bacteriocin characterization.

Advances in the preclinical characterization of the antimicrobial peptide AS-48

Antimicrobial resistance is a natural and inevitable phenomenon that constitutes a severe threat to global public health and economy. Innovative products, active against new targets and with no cross- or co-resistance with existing antibiotic classes, novel mechanisms of action, or multiple therapeutic targets are urgently required. For these reasons, antimicrobial peptides such as bacteriocins constitute a promising class of new antimicrobial drugs under investigation for clinical development. Here, we review the potential therapeutic use of AS-48, a head-to-tail cyclized cationic bacteriocin produced by Enterococcus faecalis. In the last few years, its potential against a wide range of human pathogens, including relevant bacterial pathogens and trypanosomatids, has been reported using in vitro tests and the mechanism of action has been investigated. AS-48 can create pores in the membrane of bacterial cells without the mediation of any specific receptor. However, this mechanism of action is different when susceptible parasites are studied and involves intracellular targets. Due to these novel mechanisms of action, AS-48 remains active against the antibiotic resistant strains tested. Remarkably, the effect of AS-48 against eukaryotic cell lines and in several animal models show little effect at the doses needed to inhibit susceptible species. The characteristics of this molecule such as low toxicity, microbicide activity, blood stability and activity, high stability at a wide range of temperatures or pH, resistance to proteases, and the receptor-independent effect make AS-48 unique to fight a broad range of microbial infections, including bacteria and some important parasites.

Embedding Biomimetic Magnetic Nanoparticles Coupled with Peptide AS-48 into PLGA to Treat Intracellular Pathogens

Among the strategies employed to overcome the development of multidrug-resistant bacteria, directed chemotherapy combined with local therapies (e.g., magnetic hyperthermia) has gained great interest. A nano-assembly coupling the antimicrobial peptide AS-48 to biomimetic magnetic nanoparticles (AS-48-BMNPs) was demonstrated to have potent bactericidal effects on both Gram-positive and Gram-negative bacteria when the antimicrobial activity of the peptide was combined with magnetic hyperthermia. Nevertheless, intracellular pathogens remain challenging due to the difficulty of the drug reaching the bacterium. Thus, improving the cellular uptake of the nanocarrier is crucial for the success of the treatment. In the present study, we demonstrate the embedding cellular uptake of the original nano-assembly into THP-1, reducing the toxicity of AS-48 toward healthy THP-1 cells. We optimized the design of PLGA[AS-48-BMNPs] in terms of size, colloidal stability, and hyperthermia activity (either magnetic or photothermal). The stability of the nano-formulation at physiological pH values was evaluated by studying the AS-48 release at this pH value. The influence of pH and hyperthermia on the AS-48 release from the nano-formulation was also studied. These results show a slower AS-48 release from PLGA[AS-48-BMNPs] compared to previous nano-formulations, which could make this new nano-formulation suitable for longer extended treatments of intracellular pathogens. PLGA[AS-48-BMNPs] are internalized in THP-1 cells where AS-48 is liberated slowly, which may be useful to treat diseases and prevent infection caused by intracellular pathogens. The treatment will be more efficient combined with hyperthermia or photothermia.

In vitro and in vivo production and split-intein mediated ligation (SIML) of circular bacteriocins

Circular bacteriocins are antimicrobial peptides produced by bacteria that after synthesis undergo a head-to-tail circularization. Compared to their linear counterparts, circular bacteriocins are, in general, very stable to temperature and pH changes and more resistant to proteolytic enzymes, being considered as one of the most promising groups of antimicrobial peptides for their potential biotechnological applications. Up to now, only a reduced number of circular bacteriocins have been identified and fully characterized, although many operons potentially coding for new circular bacteriocins have been recently found in the genomes of different bacterial species. The production of these peptides is very complex and depends on the expression of different genes involved in their synthesis, circularization, and secretion. This complexity has greatly limited the identification and characterization of these bacteriocins, as well as their production in heterologous microbial hosts. In this work, we have evaluated a synthetic biology approach for the in vitro and in vivo production combined with a split-intein mediated ligation (SIML) of the circular bacteriocin garvicin ML (GarML). The expression of one single gene is enough to produce a protein that after intein splicing, circularizes in an active peptide with the exact molecular mass and amino acid sequence as native GarML. In vitro production coupled with SIML has been validated with other, well described and not yet characterized, circular bacteriocins. The results obtained suggest that this synthetic biology tool holds great potential for production, engineering, improving and testing the antimicrobial activity of circular bacteriocins.

Combined Action of Antibiotics and Bacteriocins against Vancomycin-Resistant Enterococci

Antibiotics have been one of the most important discoveries in the area of applied medical microbiology; however, as a result of various factors, we are currently facing a dramatic and relatively dangerous increase in the number of cases of antibiotic resistance, and the need for new types of antimicrobials continues to grow. New approaches are needed to combat antibiotic-resistant pathogens. Bacteriocins, as part of the group of antimicrobial peptides, can be considered as alternatives and/or complements to known antibiotics. Their narrow spectra of activity can be explored for the control of various pathogens, such as vancomycin-resistant enterococci (VRE), as single therapies or in combination with known antibiotics. In the present study, we isolated bacteriocins from different lactic acid bacteria (LAB) strains, including Enterococcus and Pediococcus, and explored the possible synergistic inhibition of growth by bacteriocins and vancomycin. It was observed in the growth dynamics with previously selected VRE strains that the bacteriocins had a high specificity and a promising inhibitory effect against the VRE strains, and these results were validated by a propidium iodide viability test using flow cytometry. The data obtained indicate that the selected bacteriocins can be used to control VRE in the food industry or even as an alternative treatment to combat infections with antibiotic-resistant bacteria.

The Role of Key Amino Acids in the Antimicrobial Mechanism of a Bacteriocin Model Revealed by Molecular Simulations

The AS-48 bacteriocin is a potent antimicrobial polypeptide with enhanced stability due to its circular sequence of peptidic bonds. The mechanism of biological action is still not well understood in spite of both the elucidation of the molecular structure some years ago and several experiments performed that yielded valuable information about the AS-48 bacterial membrane poration activity. In this work, we present a computational study at an atomistic scale to analyze the membrane disruption mechanism. The process is based on the two-stage model: (1) peptide binding to the bilayer surface and (2) membrane poration due to the surface tension exerted by the peptide. Indeed, the induced membrane tension mechanism is able to explain stable formation of pores leading to membrane disruption. The atomistic detail obtained from the simulations allows one to envisage the contribution of the different amino acids during the poration process. Clustering of cationic residues and hydrophobic interactions between peptide and lipids seem to be essential ingredients in the process. GLU amino acids have shown to enhance the membrane disrupting ability of the bacteriocin. TRP24–TRP24 interactions make also an important contribution in the initial stages of the poration mechanism. The detailed atomistic information obtained from the simulations can serve to better understand bacteriocin structural characteristics to design more potent antimicrobial therapies.

Enterococcus spp. as a Producer and Target of Bacteriocins: A Double-Edged Sword in the Antimicrobial Resistance Crisis Context

Enterococcus spp. are one of the most frequent producers of bacteriocins (enterocins), which provides them with an advantage to compete in their natural environment, which is the gut of humans and many animals. The enterocins’ activity against microorganisms from different phylogenetic groups has raised interest in Enterococcus spp. in different contexts throughout the last decades, especially in the food industry. Nevertheless, some species can also cause opportunistic life-threatening infections and are frequently multidrug-resistant (MDR). Vancomycin-resistant Enterococcus (VRE), in particular, are an ongoing global challenge given the lack of therapeutic options. In this scenario, bacteriocins can offer a potential solution to this persistent threat, either alone or in combination with other antimicrobials. There are a handful of studies that demonstrate the advantages and applications of bacteriocins, especially against VRE. The purpose of this review is to present a current standpoint about the dual role of Enterococcus spp., from important producers to targets needed to be controlled, and the crucial role that enterocins may have in the expansion of enterococcal populations. Classification and distribution of enterocins, the current knowledge about the bacteriocinome of clinical enterococci, and the challenges of bacteriocin use in the fight against VRE infections are particularly detailed.

Current Knowledge of the Mode of Action and Immunity Mechanisms of LAB-Bacteriocins

Bacteriocins produced by lactic acid bacteria (LAB-bacteriocins) may serve as alternatives for aging antibiotics. LAB-bacteriocins can be used alone, or in some cases as potentiating agents to treat bacterial infections. This approach could meet the different calls and politics, which aim to reduce the use of traditional antibiotics and develop novel therapeutic options. Considering the clinical applications of LAB-bacteriocins as a reasonable and desirable therapeutic approach, it is therefore important to assess the advances achieved in understanding their modes of action, and the resistance mechanisms developed by the producing bacteria to their own bacteriocins. Most LAB-bacteriocins act by disturbing the cytoplasmic membrane through forming pores, or by cell wall degradation. Nevertheless, some of these peptides still have unknown modes of action, especially those that are active against Gram-negative bacteria. Regarding immunity, most bacteriocin-producing strains have an immunity mechanism involving an immunity protein and a dedicated ABC transporter system. However, these immunity mechanisms vary from one bacteriocin to another.

Alternatives to Fight Vancomycin-Resistant Staphylococci and Enterococci

Gram positive pathogens are a significant cause of healthcare-associated infections, with Staphylococci and Enterococci being the most prevalent ones. Vancomycin, a last resort glycopeptide, is used to fight these bacteria but the emergence of resistance against this drug leaves some patients with few therapeutic options. To counter this issue, new generations of antibiotics have been developed but resistance has already been reported. In this article, we review the strategies in place or in development to counter vancomycin-resistant pathogens. First, an overview of traditional antimicrobials already on the market or in the preclinical or clinical pipeline used individually or in combination is summarized. The second part focuses on the non-traditional antimicrobials, such as antimicrobial peptides, bacteriophages and nanoparticles. The conclusion is that there is hitherto no substitute equivalent to vancomycin. However, promising strategies based on drugs with multiple mechanisms of action and treatments based on bacteriophages possibly combined with conventional antibiotics are hoped to provide treatment options for vancomycin-resistant Gram-positive pathogens.

Antimicrobial Activity of the Circular Bacteriocin AS-48 against Clinical Multidrug-Resistant Staphylococcus aureus

The treatment and hospital-spread-control of methicillin-resistant Staphylococcus aureus (MRSA) is an important challenge since these bacteria are involved in a considerable number of nosocomial infections that are difficult to treat and produce prolonged hospitalization, thus also increasing the risk of death. In fact, MRSA strains are frequently resistant to all β-lactam antibiotics, and co-resistances with other drugs such as macrolides, aminoglycosides, and lincosamides are usually reported, limiting the therapeutical options. To this must be added that the ability of these bacteria to form biofilms on hospital surfaces and devices confer high antibiotic resistance and favors horizontal gene transfer of genetic-resistant mobile elements, the spreading of infections, and relapses. Here, we genotypically and phenotypically characterized 100 clinically isolated S. aureus for their resistance to 18 antibiotics (33% of them were OXA resistant MRSA) and ability to form biofilms. From them, we selected 48 strains on the basis on genotype group, antimicrobial-resistance profile, and existing OXA resistance to be assayed against bacteriocin AS-48. The results showed that AS-48 was active against all strains, regardless of their clinical source, genotype, antimicrobial resistance profile, or biofilm formation capacity, and this activity was enhanced in the presence of the antimicrobial peptide lysozyme. Finally, we explored the effect of AS-48 on formed S. aureus biofilms, observing a reduction in S. aureus S-33 viability. Changes in the matrix structure of the biofilms as well as in the cell division process were observed with scanning electron microscopy in both S-33 and S-48 S. aureus strains.

Broadening and Enhancing Bacteriocins Activities by Association with Bioactive Substances

Bacteriocins are antimicrobial peptides some of which are endowed with antiviral, anticancer and antibiofilm properties. These properties could be improved through synergistic interactions of these bacteriocins with other bioactive molecules such as antibiotics, phages, nanoparticles and essential oils. A number of studies are steadily reporting the effects of these combinations as new and potential therapeutic strategies in the future, as they may offer many incentives over existing therapies. In particular, bacteriocins can benefit from combination with nanoparticles which can improve their stability and solubility, and protect them from enzymatic degradation, reduce their interactions with other molecules and improve their bioavailability. Furthermore, the combination of bacteriocins with other antimicrobials is foreseen as a way to reduce the development of antibiotic resistance due to the involvement of several modes of action. Another relevant advantage of these synergistic combinations is that it decreases the concentration of each antimicrobial component, thereby reducing their side effects such as their toxicity. In addition, combination can extend the utility of bacteriocins as antiviral or anticancer agents. Thus, in this review, we report and discuss the synergistic effects of bacteriocin combinations as medicines, and also for other diverse applications including, antiviral, antispoilage, anticancer and antibiofilms.