Anti-virulence compounds against Staphylococcus aureus associated with bovine mastitis: A new therapeutic option?

Alternative treatment candidates to antibiotic therapy for bovine mastitis in the post-antibiotic era: a comprehensive review

Mastitis, an inflammation of mammary tissue frequently associated with infection, is a prevalent disease among dairy animals. Bacterial intra-mammary infection is identified as a primary cause of bovine mastitis (BM). In dairy cattle, antimicrobials are used for mastitis treatment during the lactating phase and for dry cow therapy. Although self-curing can occur, the success of mastitis treatment depends on several factors, including the type of bacteria responsible for the infection, the effectiveness of the administered antibiotics, and the host's overall immune response. Moreover, the growing resistance of microorganisms to antibiotics has restricted the available treatment options for managing intramammary infections. In addition, the utilization of critically essential antimicrobials in animals raised for food production may elevate the risk of human infections that are challenging to treat. Therefore, it is crucial to have alternative treatments with equivalent or superior effectiveness as part of any stewardship program. These may include the application of nanotechnology, stem cell technology, photodynamic and laser radiation or the use of traditional herbal medical plants, nutraceuticals, antibacterial peptides, bacteriocins, antibodies therapy, bacteriophages, phage lysins, and probiotics as alternatives to antibiotics. This review aims to discuss the potential of vaccination as an indirect strategy, along with nanotechnology, probiotics, stem cell therapy, antimicrobial peptides, photodynamic therapy, laser irradiation, and antibody treatments as direct approaches. These approaches are examined as possible alternative therapeutic options to antibiotic treatment for BM.

Disarming Staphylococcus aureus: Review of Strategies Combating This Resilient Pathogen by Targeting Its Virulence

Staphylococcus aureus is a formidable pathogen notorious for its antibiotic resistance and diverse virulence mechanisms, including toxin production, biofilm formation, and immune evasion. This article explores innovative anti-virulence strategies to disarm S. aureus by targeting critical virulence factors without exerting bactericidal pressure. Key approaches include inhibiting adhesion and biofilm formation, neutralizing toxins, disrupting quorum sensing (e.g., Agr system inhibitors), and blocking iron acquisition pathways. Additionally, interventions targeting two-component regulatory systems are highlighted. While promising, challenges such as strain variability, biofilm resilience, pharmacokinetic limitations, and resistance evolution underscore the need for combination therapies and advanced formulations. Integrating anti-virulence strategies with traditional antibiotics and host-directed therapies offers a sustainable solution to combat multidrug-resistant S. aureus, particularly methicillin-resistant strains (MRSA), and mitigate the global public health crisis.

Understanding the bovine mastitis co-infections: Coexistence with Enterobacter alters S. aureus antibiotic susceptibility and virulence phenotype

The World Health Organization recently reported an alarming evolution and spread of antibiotic resistance, a global risk factor recognized as a One Health challenge. In veterinary, the general lack of clear treatment guidelines often leads to antibiotic misuse. Bovine mastitis is responsible for major economic losses and the main cause of antibiotic administration in the dairy industry, favoring the emergence of multi-resistant phenotypes. The complexity of inter-microbial and host-pathogen interactions in the mammary gland, demonstrated by culture-independent techniques, not only complicates the prediction of antibiotic treatment outcomes but also underscores the urgent need for further research in this field. This work evaluated the interactions between S. aureus L33 and Enterobacter sp. L34 obtained from an intramammary co-infection. The behavior of the dual-species culture resembled that of the Enterobacter monoculture in all the evaluated contexts. Most of the selected S. aureus virulence factors and the antibiotic susceptibility were altered by coexisting with Enterobacter. Under the protection of Enterobacter, S. aureus was able to survive upon exposure to concentrations of cloxacillin and other antibiotics that would be bactericidal for the monoculture. This could have serious implications for bacterial clearance of mastitis originating from the underestimated co-infections. These findings highlight the importance of broadening our knowledge of how microbial interactions in intramammary infections could contribute to antibiotic treatments failures. Moreover, they open new perspectives for the design of bovine mastitis therapies that consider the ecological context in order to optimize the antibiotic usage, improve the success rates and reduce antibiotic resistance.

A review of chemical signaling mechanisms underlying quorum sensing and its inhibition in Staphylococcus aureus

Staphylococcus aureus is a significant bacterium responsible for multiple infections and is a primary cause of fatalities among patients in hospital environments. The advent of pathogenic bacteria such as methicillin-resistant S. aureus revealed the shortcomings of employing antibiotics to treat bacterial infectious diseases. Quorum sensing enhances S. aureus's survivability through signaling processes. Targeting the key components of quorum sensing has drawn much interest nowadays as a promising strategy for combating infections caused by bacteria. Concentrating on the accessory gene regulator quorum-sensing mechanism is the most commonly suggested anti-virulence approach for S.aureus. Quorum quenching is a common strategy for controlling illnesses triggered by microorganisms since it reduces the pathogenicity of bacteria and improves bacterial biofilm susceptibility to antibiotics, thus providing an intriguing prospect for drug discovery. Quorum sensing inhibition reduces selective stresses and constrains the emergence of antibiotic resistance while limiting bacterial pathogenicity. This review examines the quorum sensing mechanisms involved in S. aureus, quorum sensing targets and gene regulation, environmental factors affecting quorum sensing, quorum sensing inhibition, natural products as quorum sensing inhibitory agents and novel therapeutical strategies to target quorum sensing in S. aureus as drug developing technique to augment conventional antibiotic approaches.

Structure-based design of small molecule inhibitors of the cagT4SS ATPase Cagα of Helicobacter pylori

We here describe the structure-based design of small molecule inhibitors of the type IV secretion system of Helicobacter pylori. The secretion system is encoded by the cag pathogenicity island, and we chose Cagα, a hexameric ATPase and member of the family of VirB11-like proteins, as target for inhibitor design. We first solved the crystal structure of Cagα in a complex with the previously identified small molecule inhibitor 1G2. The molecule binds at the interface between two Cagα subunits and mutagenesis of the binding site identified Cagα residues F39 and R73 as critical for 1G2 binding. Based on the inhibitor binding site we synthesized 98 small molecule derivates of 1G2 to improve binding of the inhibitor. We used the production of interleukin-8 of gastric cancer cells during H. pylori infection to screen the potency of inhibitors and we identified five molecules (1G2_1313, 1G2_1338, 1G2_2886, 1G2_2889, and 1G2_2902) that have similar or higher potency than 1G2. Differential scanning fluorimetry suggested that these five molecules bind Cagα, and enzyme assays demonstrated that some are more potent ATPase inhibitors than 1G2. Finally, scanning electron microscopy revealed that 1G2 and its derivatives inhibit the assembly of T4SS-determined extracellular pili suggesting a mechanism for their anti-virulence effect.

Myricetin Acts as an Inhibitor of Type II NADH Dehydrogenase from Staphylococcus aureus

BACKGROUND

Staphylococcus aureus is a common pathogenic microorganism in humans and animals. Type II NADH oxidoreductase (NDH-2) is the only NADH:quinone oxidoreductase present in this organism and represents a promising target for the development of anti-staphylococcal drugs. Recently, myricetin, a natural flavonoid from vegetables and fruits, was found to be a potential inhibitor of NDH-2 of S. aureus. The objective of this study was to evaluate the inhibitory properties of myricetin against NDH-2 and its impact on the growth and expression of virulence factors in S. aureus.

RESULTS

A screening method was established to identify effective inhibitors of NDH-2, based on heterologously expressed S. aureus NDH-2. Myricetin was found to be an effective inhibitor of NDH-2 with a half maximal inhibitory concentration (IC50) of 2 μM. In silico predictions and enzyme inhibition kinetics further characterized myricetin as a competitive inhibitor of NDH-2 with respect to the substrate menadione (MK). The minimum inhibitory concentrations (MICs) of myricetin against S. aureus strains ranged from 64 to 128 μg/mL. Time-kill assays showed that myricetin was a bactericidal agent against S. aureus. In line with being a competitive inhibitor of the NDH-2 substrate MK, the anti-staphylococcal activity of myricetin was antagonized by MK-4. In addition, myricetin was found to inhibit the gene expression of enterotoxin SeA and reduce the hemolytic activity induced by S. aureus culture on rabbit erythrocytes in a dose-dependent manner.

CONCLUSIONS

Myricetin was newly discovered to be a competitive inhibitor of S. aureus NDH-2 in relation to the substrate MK. This discovery offers a fresh perspective on the anti-staphylococcal activity of myricetin.

The active ingredients in Chinese peony pods synergize with antibiotics to inhibit MRSA growth and biofilm formation

Staphylococcus aureus (S. aureus) is a zoonotic pathogen that infects both humans and animals. The rapid spread of methicillin-resistant S. aureus (MRSA) and its resistance to antibiotics, along with its ability to form biofilms, poses a serious challenge to the clinical application of traditional antibiotics. Peony (Paeonia lactiflora Pall.) is a traditional Chinese medicine with multiple pharmacological effects. This study observed the strong antibacterial and antibiofilm activity of the water extract (WE) and ethyl acetate extract (EA) of Chinese peony pods against MRSA. The combination of EA and vancomycin, cefotaxime, penicillin G or methicillin showed a synergistic or additive antibacterial and antibiofilm effects on MRSA, which is closely related to the interaction of 1,2,3,4,6-penta-O-galloyl-β-D-glucose (PG) and methyl gallate (MG). The active ingredients in peony pods have been found to increase the sensitivity of MRSA to antibiotics and demonstrate antibiofilm activity, which is mainly related to the down-regulation of global regulatory factors sarA and sigB, extracellular PIA and eDNA encoding genes icaA and cdiA, quorum sensing related genes agrA, luxS, rnaIII, hld, biofilm virulence genes psma and sspA, and genes encoding clotting factors coa and vwb, but is not related to genes that inhibit cell wall anchoring. In vivo test showed that both WE and EA were non-toxic and significantly prolonged the lifespan of G. mellonella larvae infected with MRSA. This study provides a theoretical basis for further exploration of the combined use of PG, MG and antibiotics to combat MRSA infections.

SMR peptide antagonizes Staphylococcus aureus biofilm formation

The emergence and international dissemination of multi-drug resistant Staphylococcus aureus (S. aureus) strains challenge current antibiotic-based therapies, representing an urgent threat to public health worldwide. In the U.S. alone, S. aureus infections are responsible for 11,000 deaths and 500,000 hospitalizations annually. Biofilm formation is a major contributor to antibiotic tolerance and resistance-induced delays in empirical therapy with increased infection severity, frequency, treatment failure, and mortality. Developing novel treatment strategies to prevent and disrupt biofilm formation is imperative. In this article, we test the Secretion Modification Region (SMR) peptides for inhibitory effects on resistant S. aureus biofilm-forming capacity by targeting the molecular chaperone DnaK. The dose effect of SMR peptides on biofilm formation was assessed using microtiter plate methods and confocal microscopy. Interaction between the antagonist and DnaK was determined by immune precipitation with anti-Flag M2 Affinity and Western blot analysis. Increasing SMR peptide concentrations exhibited increasing blockade of S. aureus biofilm formation with significant inhibition found at 18 µM, 36 µM, and 72 µM. This work supports the potential therapeutic benefit of SMR peptides in reducing biofilm viability and could improve the susceptibility to antimicrobial agents.IMPORTANCEThe development of anti-biofilm agents is critical to restoring bacterial sensitivity, directly combating the evolution of resistance, and overall reducing the clinical burden related to pervasive biofilm-mediated infections. Thus, in this study, the SMR peptide, a novel small molecule derived from the HIV Nef protein, was preliminarily explored for anti-biofilm properties. The SMR peptide was shown to effectively target the molecular chaperone DnaK and inhibit biofilm formation in a dose-dependent manner. These results support further investigation into the mechanism of SMR peptide-mediated biofilm formation and inhibition to benefit rational drug design and the identification of therapeutic targets.