Quorum Sensing and Toxin Production in Staphylococcus aureus Osteomyelitis: Pathogenesis and Paradox

Response of Staphylococcus aureus physiology and Agr quorum sensing to low-shear modeled microgravity

Staphylococcus aureus is commonly isolated from astronauts returning from spaceflight. Previous analysis of omics data from S. aureus low Earth orbit cultures indicated significantly increased expression of the Agr quorum sensing system and its downstream targets in spaceflight samples compared to ground controls. In this current study, the rotary cell culture system (RCCS) was used to investigate the effect of low-shear modeled microgravity (LSMMG) on S. aureus physiology and Agr activity. When cultured in the same growth medium and temperature as the previous spaceflight experiment, S. aureus LSMMG cultures exhibited decreased agr expression and altered growth compared to normal gravity control cultures, which are typically oriented with oxygenation membrane on the bottom of the high aspect rotating vessel (HARV). When S. aureus was grown in an inverted gravity control orientation (oxygenation membrane on top of the HARV), reduced Agr activity was observed relative to both traditional control and LSMMG cultures, signifying that oxygen availability may affect the observed differences in Agr activity. Metabolite assays revealed increased lactate and decreased acetate excretion in both LSMMG and inverted control cultures. Secretomics analysis of LSMMG, control, and inverted control HARV culture supernatants corroborated these results, with inverted and LSMMG cultures exhibiting a decreased abundance of Agr-regulated virulence factors and an increased abundance of proteins expressed in low-oxygen conditions. Collectively, these studies suggest that the orientation of the HARV oxygenation membrane can affect S. aureus physiology and Agr quorum sensing in the RCCS, a variable that should be considered when interpreting data using this ground-based microgravity model.IMPORTANCES. aureus is commonly isolated from astronauts returning from spaceflight and from surfaces within human-inhabited closed environments such as spacecraft. Astronaut health and immune function are significantly altered in spaceflight. Therefore, elucidating the effects of microgravity on S. aureus physiology is critical for assessing its pathogenic potential during long-term human space habitation. These results also highlight the necessity of eliminating potential confounding factors when comparing simulated microgravity model data with actual spaceflight experiments.

Jellyfish protein hydrolysates: Multifunctional bioactivities unveiled in the battle against diabetes, inflammation, and bacterial pathogenesis

This study investigates the multifunctional bioactivities of pepsin-hydrolyzed jellyfish by-products (Rhopilema hispidum and Lobonema smithii), focusing on their anti-α-glucosidase activity, anti-inflammatory effects, anti-bacterial properties, and ability to inhibit biofilm formation of Staphylococcus aureus. Our findings revealed that jellyfish protein hydrolysates, particularly from Rhopilema hispidum, exhibit significant anti-α-glucosidase activity, surpassing the well-known α-glucosidase inhibitor Acarbose. Furthermore, we demonstrated the anti-inflammatory capabilities of these hydrolysates in suppressing lipopolysaccharide (LPS)-induced nitric oxide production in murine macrophage cells. This effect was dose-dependent and non-cytotoxic, highlighting the hydrolysate potential in treating inflammation-related conditions. Regarding anti-bacterial activity, pepsin-hydrolyzed jellyfish selectively exhibited a potent effect against S. aureus, including Methicillin-susceptible and Methicillin-resistant strains. This activity was evident at minimum inhibitory concentrations (MIC) of 25 μg/mL for S. aureus ATCC10832, while a modest effect was observed against other Gram-positive strains. The hydrolysates effectively delayed bacterial growth dose-dependently, suggesting their use as alternative agents against bacterial infections. Most notably, pepsin-hydrolyzed jellyfish showed significant anti-biofilm activity against S. aureus. The umbrella section hydrolysate of Rhopilema hispidum was particularly effective, reducing biofilm formation through downregulating the icaA gene, crucial for biofilm development. Furthermore, the hydrolysates modulated the expression of the agrA gene, a key regulator in the pathogenesis of S. aureus. In conclusion, pepsin-hydrolyzed jellyfish protein hydrolysates exhibit promising multifunctional bioactivities, including anti-diabetic, anti-inflammatory, antibacterial, and anti-biofilm properties. These findings suggest their potential application in pharmaceutical and nutraceutical fields, particularly in managing diabetic risks, inflammation, bacterial infections, and combating the biofilm-associated pathogenicity of S. aureus.

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.

Emerging strategies and therapeutic innovations for combating drug resistance in Staphylococcus aureus strains: A comprehensive review

In recent years, antibiotic therapy has encountered significant challenges due to the rapid emergence of multidrug resistance among bacteria responsible for life-threatening illnesses, creating uncertainty about the future management of infectious diseases. The escalation of antimicrobial resistance in the post-COVID era compared to the pre-COVID era has raised global concern. The prevalence of nosocomial-related infections, especially outbreaks of drug-resistant strains of Staphylococcus aureus, have been reported worldwide, with India being a notable hotspot for such occurrences. Various virulence factors and mutations characterize nosocomial infections involving S. aureus. The lack of proper alternative treatments leading to increased drug resistance emphasizes the need to investigate and examine recent research to combat future pandemics. In the current genomics era, the application of advanced technologies such as next-generation sequencing (NGS), machine learning (ML), and quantum computing (QC) for genomic analysis and resistance prediction has significantly increased the pace of diagnosing drug-resistant pathogens and insights into genetic intricacies. Despite prompt diagnosis, the elimination of drug-resistant infections remains unattainable in the absence of effective alternative therapies. Researchers are exploring various alternative therapeutic approaches, including phage therapy, antimicrobial peptides, photodynamic therapy, vaccines, host-directed therapies, and more. The proposed review mainly focuses on the resistance journey of S. aureus over the past decade, detailing its resistance mechanisms, prevalence in the subcontinent, innovations in rapid diagnosis of the drug-resistant strains, including the applicants of NGS and ML application along with QC, it helps to design alternative novel therapeutics approaches against S. aureus infection.

Differential survival of Staphylococcal species in macrophages

Staphylococcus aureus is considered an extracellular pathogen, yet the bacterium is able to survive within and escape from host cells. An agr/sae mutant of strain USA300 is unable to escape from macrophages but can replicate and survive within. We questioned whether such "non-toxic" S. aureus resembles the less pathogenic coagulase-negative Staphylococcal (CoNS) species like S. epidermidis, S. carnosus, S. lugdunensis, S. capitis, S. warneri, or S. pettenkoferi. We show that the CoNS are more efficiently killed in macrophage-like THP-1 cells or in human primary macrophages. Mutations in katA, copL, the regulatory system graRS, or sigB did not impact bacterial survival in THP-1 cells. Deletion of the superoxide dismutases impaired S. aureus survival in primary macrophages but not in THP-1 cells. However, expression of the S. aureus-specific sodM in S. epidermidis was not sufficient to protect this species from being killed. Thus, at least in those cells, better bacterial survival of S. aureus could not be linked to higher protection from ROS. However, "non-toxic" S. aureus was found to be insensitive to pH, whereas most CoNS were protected when phagosomal acidification was inhibited. Thus, species differences are at least partially linked to differences in sensitivity to acidification.

Thwarting resistance: MgrA inhibition with methylophiopogonanone a unveils a new battlefront against S. aureus

Limitations in the clinical treatment of Staphylococcus aureus (S. aureus) infections have arisen due to the advent of antibiotic-resistant strains. Given the immense potential of therapeutic strategies targeting bacterial virulence, the role of MgrA as a pivotal virulence determinant in S. aureus-orchestrating resistance, adherence, and hundreds of virulence targets-becomes indispensable. In this investigation, leveraging advanced virtual screening and fluorescence anisotropy assays, we discerned methylophiopogonanone A (Mo-A), a flavonoid derivative, as a potent disruptor of the MgrA-DNA interaction nexus. Subsequent analysis revealed that Mo-A effectively inhibits the expression of virulence factors such as Hla and Pvl in S. aureus and markedly reduces its adhesion capability to fibrinogen. On a cellular landscape, Mo-A exerts a mitigating influence on the deleterious effects inflicted by S. aureus USA300 on A549 cells. Furthermore, our data indicate that Mo-A downregulates the transcription of genes associated with immune evasion, such as nucleases (nuc), Staphylococcal Chemotaxis Inhibitory Protein (chips), and Staphylococcal Complement Inhibitor (scin), thereby undermining immune escape and amplifying neutrophil chemotaxis. Upon application in an in vivo setting, Mo-A assumes a protective persona in a murine model of S. aureus USA300-induced pneumonia and demonstrates efficacy in the Galleria mellonella infection model. Of note, S. aureus displayed no swift acquisition of resistance to Mo-A, and the effect was synergistically enhanced when used in combination with vancomycin. Our findings add substantive weight to the expanding field of virulence-targeted therapeutic strategies and set the stage for more comprehensive exploration of Mo-A potential in combating antibiotic-resistant S. aureus.

Staphylococcus aureus From an Acute Fracture-related Infection Displays Important Bacteriological and Histopathologic Differences From a Chronic Equivalent in a Murine Bone Infection Model

BACKGROUND

Staphylococcus aureus is the leading pathogen in fracture-related infection. Previous in vitro experiments, in vivo testing in wax moth larvae, and genomic analysis of clinical S. aureu s isolates from fracture-related infection identified low-virulence (Lo-SA5464) and high-virulence (Hi-SA5458) strains. These findings correlated with acute fracture-related infection induced by Hi-SA5458, whereas Lo-SA5464 caused a chronic fracture-related infection in its human host. However, it remains unclear whether and to what extent the causative pathogen is attributable to these disparities in fracture-related infections.

QUESTION/PURPOSE

Are there differences in the course of infection when comparing these two different clinical isolates in a murine fracture-related infection model, as measured by (1) clinical observations of weight loss, (2) quantitative bacteriology, (3) immune response, and (4) radiographic and histopathologic morphology?

METHODS

Twenty-five (including one replacement animal) female (no sex-specific influences expected), skeletally mature C57Bl/6N inbred mice between 20 and 28 weeks old underwent femoral osteotomy stabilized by titanium locking plates. Fracture-related infection was established by inoculation of high-virulence S. aureus EDCC 5458 (Hi-SA5458) or low-virulence S. aureus EDCC 5464 (Lo-SA5464) in the fracture gap. Each of these groups consisted of 12 randomly assigned animals. Mice were euthanized 4 and 14 days postsurgery, resulting in six animals per group and timepoint. The severity and progression of infection were assessed in terms of clinical observation of weight loss, quantitative bacteriology, quantitative serum cytokine levels, qualitative analysis of postmortem radiographs, and semiquantitative histopathologic evaluation.

RESULTS

For clinical observations of weight change, no differences were seen at Day 4 between Hi-SA5458- and Lo-SA5464-infected animals (mean -0.6 ± 0.1 grams versus -0.8 ± 0.2 grams, mean difference -0.2 grams [95% CI -0.8 to 0.5 grams]; p =0.43), while at 14 days, the Hi-SA5458 group lost more weight than the Lo-SA5464 group (mean -1.55 ± 0.2 grams versus -0.8 ± 0.3 grams; mean difference 0.7 grams [95% CI 0.2 to 1.3 grams]; p = 0.02). Quantitative bacteriological results 4 days postoperatively revealed a higher bacterial load in soft tissue samples in Hi-SA5458-infected animals than in the Lo-SA5464-infected cohort (median 6.8 x 10 7 colony-forming units [CFU]/g, range 2.2 x 10 7 to 2.1 x 10 9 CFU/g versus median 6.0 x 10 6 CFU/g, range 1.8 x 10 5 to 1.3 x 10 8 CFU/g; difference of medians 6.2 x 10 7 CFU/g; p = 0.03). At both timepoints, mice infected with the Hi-SA5458 strain also displayed higher proportions of bacterial dissemination into organs than Lo-SA5464-infected animals (67% [24 of 36 organs] versus 14% [five of 36 organs]; OR 12.0 [95% CI 3.7 to 36]; p < 0.001). This was accompanied by a pronounced proinflammatory response on Day 14, indicated by increased serum cytokine levels of interleukin-1β (mean 9.0 ± 2.2 pg/mL versus 5.3 ± 1.5 pg/mL; mean difference 3.6 pg/mL [95% CI 2.0 to 5.2 pg/mL]; p < 0.001), IL-6 (mean 458.6 ± 370.7 pg/mL versus 201.0 ±89.6 pg/mL; mean difference 257.6 pg/mL [95% CI 68.7 to 446.5 pg/mL]; p = 0.006), IL-10 (mean 15.9 ± 3.5 pg/mL versus 9.9 ± 1.0 pg/mL; mean difference 6.0 pg/mL [95% CI 3.2 to 8.7 pg/mL]; p < 0.001), and interferon-γ (mean 2.7 ± 1.9 pg/mL versus 0.8 ± 0.3 pg/mL; mean difference 1.8 pg/mL [95% CI 0.5 to 3.1 pg/mL]; p = 0.002) in Hi-SA5458-infected compared with Lo-SA5464-infected animals. The semiquantitative histopathologic assessment on Day 4 revealed higher grades of granulocyte infiltration in Hi-SA5458-infected animals (mean grade 2.5 ± 1.0) than in Lo-SA5464-infected animals (mean grade 1.8 ± 1.4; mean difference 0.7 [95% CI 0.001 to 1.4]; p = 0.0498). On Day 14, bone healing at the fracture site was present to a higher extent in Lo-SA5464-infected animals than in Hi-SA5458-infected animals (mean grade 0.2 ± 0.4 versus 1.8 ± 1.2; mean difference -1.6 [95% CI -2.8 to -0.5]; p = 0.008).

CONCLUSION

Similar to septic infection in a human host, infection with Hi-SA5458 in this murine model was characterized by a higher bacterial load, more-pronounced systemic dissemination, and stronger systemic and local inflammation. Thus, there is strong support for the idea that pathogenic virulence plays a crucial role in fracture-related infections. To confirm our observations, future studies should focus on characterizing S. aureus virulence at the genomic and transcriptomic levels in more clinical isolates and patients. Comparing knockout and wildtype strains in vitro and in vivo, including the S. aureus strains studied, could confirm our findings and identify the genomic features responsible for S. aureus virulence in fracture-related infections.

CLINICAL RELEVANCE

For translational use, virulence profiles of S. aureus may be useful in guiding treatment decisions in the future. Once specific virulence targets are identified, one approach to fracture-related infections with high-virulence strains might be the development of antivirulence agents, particularly to treat or prevent septic dissemination. For fracture-related infections with low virulence, prolonged antimicrobial therapy or exchange of an indwelling implant might be beneficial owing to slower growth and persistence capacity.

Integrative tissue, cellular and molecular responsiveness of an innovative ex vivo model of the Staphylococcus aureus-mediated bone infection

Osteomyelitis is a pathological condition of the bone, frequently associated with the presence of infectious agents - namely Staphylococcus aureus - that induce inflammation and tissue destruction. Recent advances in the understanding of its pathophysiology and the identification of innovative therapeutic approaches were gathered from experimental in vitro and in vivo systems. However, cell culture models offer limited representativeness of the cellular functionality and the cell-cell and cell-matrix interactions, further failing to mimic the three-dimensional tissue organization; and animal models allow for limited mechanistic assessment given the complex nature of systemic and paracrine regulatory systems and are endorsed with ethical constraints. Accordingly, this study aims at the establishment and assessment of a new ex vivo bone infection model, upon the organotypic culture of embryonic chicken femurs colonized with S. aureus, highlighting the model responsiveness at the molecular, cellular, and tissue levels. Upon infection with distinct bacterial inoculums, data reported an initial exponential bacterial growth, followed by diminished metabolic activity. At the tissue level, evidence of S. aureus-mediated tissue destruction was attained and demonstrated through distinct methodologies, conjoined with decreased osteoblastic/osteogenic and increased osteoclastic/osteoclastogenic functionalities-representative of the osteomyelitis clinical course. Overall, the establishment and characterization of an innovative bone tissue infection model that is simple, reproducible, easily manipulated, cost-effective, and simulates many features of human osteomyelitis, further allowing the maintenance of the bone tissue's three-dimensional morphology and cellular arrangement, was achieved. Model responsiveness was further demonstrated, showcasing the capability to improve the research pipeline in bone tissue infection-related research.

Electron beam irradiation degrades the toxicity and alters the protein structure of Staphylococcus aureus alpha-hemolysin

α-Hemolysin (Hla) is a potent pore-forming toxin (PFT) produced by Staphylococcus aureus that exacerbates the pathogenesis of S. aureus enterotoxicity and plays a role in population food poisoning. Hla lyses cells by binding to host cell membranes and oligomerizing to form heptameric structures, thereby disrupting the cell barrier. Although the broad bactericidal effect of electron beam irradiation (EBI) has been demonstrated whether it has a damaging or degrading effect on Hla's remains unknown. In this study, EBI was found to have the effect of altering the secondary structure of Hla proteins, verifying that the damaging effect of EBI-treated Hla on intestinal and skin epithelial cell barriers was significantly reduced. It was noted by hemolysis and protein interactions that EBI treatment significantly disrupted the binding of Hla to its high-affinity receptor, but did not affect the binding between Hla monomers to form heptamers. Thus, EBI can effectively reduce the threat of Hla to food safety.

Computational exploration of natural compounds targeting Staphylococcus aureus: inhibiting AgrA promoter binding for antimicrobial intervention

Staphylococcus aureus is a highly virulent nosocomial pathogen that poses a significant threat to individuals exposed to healthcare settings. Due to its sophisticated machinery for producing virulence factors, S. aureus can cause severe and potentially fatal infections in humans. This study focuses on the response regulator AgrA, which plays a crucial role in regulating the production of virulence factors in S. aureus. The objective is to identify natural compounds that can inhibit the binding of AgrA to its promoter site, thus inhibiting the expression of virulence genes. To achieve this, a pharmacophore model was generated using known drugs and applied to screen the ZINC natural product database. The resulting compounds were subjected to molecular docking-based virtual screening against the C-terminal DNA binding domain of AgrA. Three compounds, namely ZINC000077269178, ZINC000051012304, and ZINC000004266026, were shortlisted based on their strong affinity for key residues involved in DNA binding and transcription initiation. Subsequently, the unbound and ligand-bound complexes were subjected to a 200 ns molecular dynamics simulation to assess their conformational stability. Various analyses, including RMSD, RMSF, Rg, SASA, Principal Component Analysis, and Gibbs free energy landscape, were conducted on the simulation trajectory. The RMSD profile indicated similar fluctuations in both bound and unbound structures, while the Rg profile demonstrated the compactness of the protein without any unfolding during the simulation. Furthermore, Principal component analysis revealed that ligand binding reduced the overall atomic motion of the protein whereas free energy landscape suggested the energy variations obtained in complexes.Communicated by Ramaswamy H. Sarma.

Role of sodium pyruvate in maintaining the survival and cytotoxicity of Staphylococcus aureus under high glucose conditions

Glucose is a crucial carbon source for the growth of Staphylococcus aureus, but an excess of glucose is detrimental and even leads to cell death. Pyruvate, the central metabolite of glycolysis, has been shown to have anti-inflammatory and antioxidant properties. This study aimed to investigate the protective effect of pyruvate on S. aureus under high glucose conditions. Sodium pyruvate greatly increased the cytotoxicity of S. aureus strain BAA-1717 to human erythrocytes and neutrophils in vitro. However, the cytotoxicity and survival of S. aureus were significantly reduced by high glucose, which was restored to normal levels by the addition of sodium pyruvate. The expression of hlg and lukS in S. aureus was higher in the LB-GP cultures than that in LB-G cultures, but there was no significant difference in cytotoxicity between LB-GP and LB-G cultures. Furthermore, the hemolytic activity of S. aureus supernatants could be inhibited by the cell-free culture medium (CFCM) of LB-G cultures, suggesting that high levels of extracellular proteases were presence in the CFCM of LB-G cultures, resulting in degradation of the hemolytic factors. The expression of sarA, which negatively regulates extracellular protease secretion, was higher in LB-GP cultures than that in LB-G cultures. Additionally, sodium pyruvate increased acetate production in S. aureus, which helps maintain cell viability under acidic environment. In conclusion, pyruvate plays an important role in the survival and cytotoxicity of S. aureus under high glucose conditions. This finding may aid in the development of effective treatments for diabetic foot infections.

Flavone inhibits Staphylococcus aureus virulence via inhibiting the sae two component system

The rising prevalence of antibiotic resistance in Staphylococcus aureus calls for the development of innovative antimicrobial agents targeting novel pathways. S. aureus generates various virulence factors that compromise host defense mechanisms. Flavone, a core structure of flavonoids, has been shown to diminish the production of staphyloxanthin and alpha-hemolysin. Nonetheless, the influence of flavone on the majority of other virulence factors in S. aureus and its underlying molecular mechanism remain elusive. In this study, we examined the impact of flavone on the transcriptional profile of S. aureus using transcriptome sequencing. Our findings revealed that flavone substantially downregulated the expression of over 30 virulence factors implicated in immune evasion by the pathogen. Gene set enrichment analysis of the fold change-ranked gene list in relation to the Sae regulon indicated a robust association between flavone-induced downregulation and membership in the Sae regulon. Through the analysis of Sae target promoter-gfp fusion expression patterns, we observed a dose-dependent inhibition of Sae target promoter activity by flavone. Moreover, we discovered that flavone protected human neutrophils from S. aureus-mediated killing. Flavone also decreased the expression of alpha-hemolysin and other hemolytic toxins, resulting in a reduction in S. aureus' hemolytic capacity. Additionally, our data suggested that the inhibitory effect of flavone on the Sae system operates independently of its capacity to lower staphyloxanthin levels. In conclusion, our study proposes that flavone exhibits a broad inhibitory action on multiple virulence factors of S. aureus by targeting the Sae system, consequently diminishing the bacterium's pathogenicity.

Hyperglycemia Increases Severity of Staphylococcus aureus Osteomyelitis and Influences Bacterial Genes Required for Survival in Bone

Hyperglycemia, or elevated blood glucose, renders individuals more prone to developing severe Staphylococcus aureus infections. S. aureus is the most common etiological agent of musculoskeletal infection, which is a common manifestation of disease in hyperglycemic patients. However, the mechanisms by which S. aureus causes severe musculoskeletal infection during hyperglycemia are incompletely characterized. To examine the influence of hyperglycemia on S. aureus virulence during invasive infection, we used a murine model of osteomyelitis and induced hyperglycemia with streptozotocin. We discovered that hyperglycemic mice exhibited increased bacterial burdens in bone and enhanced dissemination compared to control mice. Furthermore, infected hyperglycemic mice sustained increased bone destruction relative to euglycemic controls, suggesting that hyperglycemia exacerbates infection-associated bone loss. To identify genes contributing to S. aureus pathogenesis during osteomyelitis in hyperglycemic animals relative to euglycemic controls, we used transposon sequencing (TnSeq). We identified 71 genes uniquely essential for S. aureus survival in osteomyelitis in hyperglycemic mice and another 61 mutants with compromised fitness. Among the genes essential for S. aureus survival in hyperglycemic mice was the gene encoding superoxide dismutase A (sodA), one of two S. aureus superoxide dismutases involved in detoxifying reactive oxygen species (ROS). We determined that a sodA mutant exhibits attenuated survival in vitro in high glucose and in vivo during osteomyelitis in hyperglycemic mice. SodA therefore plays an important role during growth in high glucose and promotes S. aureus survival in bone. Collectively, these studies demonstrate that hyperglycemia increases the severity of osteomyelitis and identify genes contributing to S. aureus survival during hyperglycemic infection.

Effect and Mechanism of Eliminating Staphylococcus aureus by Electron Beam Irradiation and Reducing the Toxicity of Its Metabolites

The purpose of this study was to evaluate the mechanism of sterilization of Staphylococcus aureus by electron beam irradiation (0.5-, 1-, 2-, 4-, and 6-kGy treatments) and whether it reduces the toxicity of its fermentation supernatant. In this study, we investigated the mechanism of sterilization of S. aureus by electron beam irradiation using colony count, membrane potential, intracellular ATP, and UV absorbance measurements; we used hemolytic, cytotoxic, and suckling mouse wound models to verify that electron beam irradiation reduced the toxicity of the S. aureus fermentation supernatant. The results showed that 2 kGy of electron beam irradiation treatment completely inactivated S. aureus in suspension culture, and 4 kGy inactivated cells in S. aureus biofilms. This study suggests that the bactericidal effect of electron beam irradiation on S. aureus may be attributed to reversible damage to the cytoplasmic membrane, resulting in its leakage and the significant degradation of genomic DNA. The combined results of hemolytic, cytotoxic, and suckling mouse wound models demonstrated that the toxicity of S. aureus metabolites was significantly reduced when the electron beam irradiation dose was 4 kGy. In summary, electron beam irradiation has the potential to control S. aureus and reduce its toxic metabolites in food. IMPORTANCE Electron beam irradiation of >1 kGy damaged the cytoplasmic membrane, and reactive oxygen species (ROS) penetrated the cells. Electron beam irradiation of >4 kGy reduces the combined toxicity of virulent proteins produced by Staphylococcus aureus. Electron beam irradiation of >4 kGy can be used to inactivate Staphylococcus aureus and biofilms on milk.

Antimicrobial Activities and Biofilm Inhibition Properties of Trigonella foenumgraecum Methanol Extracts against Multidrug-Resistant Staphylococcus aureus and Escherichia coli

Multidrug-resistant bacteria are becoming the leading cause of death globally due to their resistance to many currently used antibiotics. Bacteria naturally have intrinsic resistance or acquired resistance to certain commonly used antibiotics. Therefore, searching for novel compounds has become necessary. Trigonella foenumgraecum extract was evaluated for antimicrobial and antibiofilm activities against multidrug-resistant bacteria Staphylococcus aureus and Escherichia coli. The minimum inhibitory concentration and minimum bactericidal concentration of the extract were also determined. Moreover, gas chromatography-mass spectrometry (GC-MS) analysis was used to identify the phytochemical components present in the extract. GC-MS analysis revealed that T. foenumgraecum extract contains major compounds such as Phenol, 2-methoxy-3-(2-propenyl)-, n-Hexadecanoic acid, and 9,12,15-Octadecatrienoic acid. Both bacterial strains showed resistance to some of the antibiotics tested. T. foenumgraecum showed inhibitory activity against the tested bacterial strains with a MIC of 500 µg/mL and MBC of 1000 µg/mL. The methanol extract decreased the biofilm activity of both E. coli and S. aureus below the sub-minimum inhibitory concentration. The extract showed antibacterial and antibiofilm activity against the tested bacterial pathogens.

Critical Assessment of the Prospects of Quorum-Quenching Therapy for Staphylococcus aureus Infection

Staphylococcus aureus is an important pathogen that causes a high number of infections and is one of the leading causes of death in hospitalized patients. Widespread antibiotic resistance such as in methicillin-resistant S. aureus (MRSA) has prompted research into potential anti-virulence-targeted approaches. Targeting the S. aureus accessory gene regulator (Agr) quorum-sensing system, a master regulator of virulence, is the most frequently proposed anti-virulence strategy for S. aureus. While much effort has been put into the discovery and screening for Agr inhibitory compounds, in vivo analysis of their efficacy in animal infection models is still rare and reveals various shortcomings and problems. These include (i) an almost exclusive focus on topical skin infection models, (ii) technical problems that leave doubt as to whether observed in vivo effects are due to quorum-quenching, and (iii) the discovery of counterproductive biofilm-increasing effects. Furthermore, potentially because of the latter, invasive S. aureus infection is associated with Agr dysfunctionality. Altogether, the potential of Agr inhibitory drugs is nowadays seen with low enthusiasm given the failure to provide sufficient in vivo evidence for their potential after more than two decades since the initiation of such efforts. However, current Agr inhibition-based probiotic approaches may lead to a new application of Agr inhibition strategies in preventing S. aureus infections by targeting colonization or for otherwise difficult-to-treat skin infections such as atopic dermatitis.

In Silico Genome-Scale Analysis of Molecular Mechanisms Contributing to the Development of a Persistent Infection with Methicillin-Resistant Staphylococcus aureus (MRSA) ST239

The increasing frequency of isolation of methicillin-resistant Staphylococcus aureus (MRSA) limits the chances for the effective antibacterial therapy of staphylococcal diseases and results in the development of persistent infection such as bacteremia and osteomyelitis. The aim of this study was to identify features of the MRSA_ST239 0943-1505-2016 (SA943) genome that contribute to the formation of both acute and chronic musculoskeletal infections. The analysis was performed using comparative genomics data of the dominant epidemic S. aureus lineages, namely ST1, ST8, ST30, ST36, and ST239. The SA943 genome encodes proteins that provide resistance to the host's immune system, suppress immunological memory, and form biofilms. The molecular mechanisms of adaptation responsible for the development of persistent infection were as follows: amino acid substitution in PBP2 and PBP2a, providing resistance to ceftaroline; loss of a large part of prophage DNA and restoration of the nucleotide sequence of beta-hemolysin, that greatly facilitates the escape of phagocytosed bacteria from the phagosome and formation of biofilms; dysfunction of the AgrA system due to the presence of psm-mec and several amino acid substitutions in the AgrC; partial deletion of the nucleotide sequence in genomic island vSAβ resulting in the loss of two proteases of Spl-operon; and deletion of SD repeats in the SdrE amino acid sequence.

The implications of quorum sensing inhibition in bacterial antibiotic resistance- with a special focus on aquaculture

The aquaculture industry is an expanding and demanding industry and due to an increase in urbanization, with rise in income of developing countries population, it offers to provide a sustainable food supply. However, the industry is facing a number of challenges, out of which few needs to be tackled immediately to maximise the productivity. An upcoming problem is the emergence of antibiotic resistant pathogens due to the unchecked use of antibiotics in aquaculture and human clinical practices. A wide variety of aquatic pathogens such as Edwardsiella, Vibrio, and Aeromonas spp. use quorum sensing (QS) systems, a regulatory process involving cell communication via signalling molecules for the collective function of pathogens which regulates the genes expression including virulent genes. Quorum sensing results in bacterial biofilms formation, which leads to their reduced susceptibility towards antimicrobial agents. The usage of quorum sensing inhibitors (QSIs) has been proposed as an attractive strategy to tackle this problem. Due to the modulation of virulence genes expression, QSIs can be used as novel and viable approach to overcome antibiotic resistance in aquaculture. In this review, we direct our attention to the quorum sensing phenomenon and its viability as a target pathway for tackling the ever-growing problem of antimicrobial resistance in aquaculture. This review also provides a concise compilation of the currently available QSIs and investigates possible natural sources for quorum quenching.

Human Osteoblast-Conditioned Media Can Influence Staphylococcus aureus Biofilm Formation

Osteoblasts are bone-forming and highly active cells participating in bone homeostasis. In the case of osteomyelitis and more specifically prosthetic joint infections (PJI) for which Staphylococcus aureus (S. aureus) is mainly involved, the interaction between osteoblasts and S. aureus results in impaired bone homeostasis. If, so far, most of the studies of osteoblasts and S. aureus interactions were focused on osteoblast response following direct interactions with co-culture and/or internalization models, less is known about the effect of osteoblast factors on S. aureus biofilm formation. In the present study, we investigated the effect of human osteoblast culture supernatant on methicillin sensitive S. aureus (MSSA) SH1000 and methicillin resistant S. aureus (MRSA) USA300. Firstly, Saos-2 cell line was incubated with either medium containing TNF-α to mimic the inflammatory periprosthetic environment or with regular medium. Biofilm biomass was slightly increased for both strains in the presence of culture supernatant collected from Saos-2 cells, stimulated or not with TNF-α. In such conditions, SH1000 was able to develop microcolonies, suggesting a rearrangement in biofilm organization. However, the biofilm matrix and regulation of genes dedicated to biofilm formation were not substantially changed. Secondly, culture supernatant obtained from primary osteoblast culture induced varied response from SH1000 strain depending on the different donors tested, whereas USA300 was only slightly affected. This suggested that the sensitivity to bone cell secretions is strain dependent. Our results have shown the impact of osteoblast secretions on bacteria and further identification of involved factors will help to manage PJI.

Magnetic Composite Rapidly Treats Staphylococcus aureus-Infected Osteomyelitis through Microwave Strengthened Thermal Effects and Reactive Oxygen Species

It is difficult to effectively treat bacterial osteomyelitis using photothermal therapy or photodynamic therapy due to poor penetration of light. Here, a microwave (MW)-excited magnetic composite of molybdenum disulfide (MoS₂ ) / iron oxide (Fe₃ O₄ ) is reported for the treatment of bacteria-infected osteomyelitis. In in vitro and in vivo experiments, MoS₂ /Fe₃ O₄ is shown to effectively eradicate bacteria-infected mouse tibia osteomyelitis, due to MW thermal enhancement and reactive oxygen species (ROS) (¹ O₂ and ·O₂ ^- ) production under MW radiation. In addition, the mechanism of MW heat generation is proposed by MW network vector analysis. By the density functional theory and finite element method, the ROS generation mechanism is proposed. The synergy or conductive network between dielectric MoS₂ and magnetic Fe₃ O₄ can reach both enhancement of the dielectric and magnetic attenuation capability. In addition, abundant interfaces are generated to enhance the attenuation of electromagnetic waves by MoS₂ and Fe₃ O_4, introducing multiple reflections and interfacial polarization. Therefore, MoS₂ /Fe₃ O₄ has excellent MW absorption ability based on the synergy or conductive network between MoS₂ and magnetic Fe₃ O₄ as well as multiple dielectric reflections and interfacial polarization.

Pyrancoumarin derivative LP4C targeting of pyrimidine de novo synthesis pathway inhibits MRSA biofilm and virulence

Staphylococcus aureus poses a serious public health threat because of its multidrug resistance and biofilm formation ability. Hence, developing novel anti-biofilm agents and finding targets are needed to mitigate the proliferation of drug-resistant pathogens. In our previous study, we showed that the pyrancoumarin derivative 2-amino-4-(2,6-dichlorophenyl)-3-cyano-5-oxo-4H, 5H- pyrano [3,2c] chromene (LP4C) can destroy the biofilm of methicillin-resistant S. aureus (MRSA) in vitro and in vivo. Here, we further explored the possible mechanism of LP4C as a potential anti-biofilm drug. We found that LP4C inhibits the expression of enzymes involved in the de novo pyrimidine pathway and attenuates the virulence of MRSA USA300 strain without affecting the agr or luxS quorum sensing system. The molecular docking results indicated that LP4C forms interactions with the key amino acid residues of pyrR protein, which functions as the important regulator of bacterial pyrimidine synthesis. These findings reveal that pyrancoumarin derivative LP4C inhibits MRSA biofilm formation and targeting pyrimidine de novo synthesis pathway.

Assessment of the bifidogenic and antibacterial activities of xylooligosaccharide

Xylooligosaccharide (XOS) is an attractive prebiotic mainly due to its bifidogenic effect. However, commercial XOS with different compositions is often applied in the food industry at different doses without specifications. In this study, we evaluated the bifidogenic activity of XOS at different doses with either mixtures or pure fractions with different degrees of polymerization (DP), using three strains of Bifidobacterium spp., including B. breve ATCC 15700, B. bifidum ATCC 29521, and B. animalis subsp. lactis HN019. Three growth indicators showed strain-specific bifidogenic activity of XOS, and the activity was both dose- and fraction-dependent as only certain fractions stimulated significant growth. Adding 0.25% XOS (w/v) also promoted increase in total bifidobacterial population of rat fecal samples fermented in vitro. Albeit the antibacterial activity of XOS fractions can be demonstrated, significant growth inhibition can only be achieved when 4.0% XOS mixture was added in Staphylococcus aureus ATCC 6538 pure culture. In contrast, in the presence of B. lactis HN019, 1.0% XOS showed significant antibacterial activity against S. aureus ATCC 6538 in milk. In addition, RNA sequencing suggested downregulation of genes involved in S. aureus ATCC 6538 infection, pathogenesis, and quorum sensing, by XOS. In conclusion, the report urges scientific specifications on XOS chemistry for its effective application as a novel food ingredient or functional food and provides novel insights into its bifidogenic and antibacterial activities.

Terpenes Combinations Inhibit Biofilm Formation in Staphyloccocus aureus by Interfering with Initial Adhesion

The biofilm is a conglomerate of cells surrounded by an extracellular matrix, which contributes to the persistence of infections. The difficulty in removing the biofilm drives the research for new therapeutic options. In this work, the effect of terpenes (−)-trans-Caryophyllene, (S)-cis-Verbenol, (S)-(−)-Limonene, (R)-(+)-Limonene, and Linalool was evaluated, individually and in combinations on bacterial growth, by assay with resazurin; the formation of biofilm, by assay with violet crystal; and the expression of associated genes, by real-time PCR, in two clinical isolates of Staphyloccocus aureus, ST30-t019 and ST5-t311, responsible for more than 90% of pediatric infections by this pathogen in Paraguay. All combinations of terpenes can inhibit biofilm formation in more than 50% without affecting bacterial growth. The most effective combination was (−)-trans-Caryophyllene and Linalool at a 500 μg/mL concentration for each, with an inhibition percentage of 88%. This combination decreased the expression levels of the sdrD, spa, agr, and hld genes associated with the initial cell adhesion stage and quorum sensing. At the same time, it increased the expression levels of the cap5B and cap5C genes related to the production of capsular polysaccharides. The combinations of compounds tested are promising alternatives to inhibit biofilm formation in S. aureus.

Molecular Mechanisms of Drug Resistance in Staphylococcus aureus

This paper discusses the mechanisms of S. aureus drug resistance including: (1) introduction. (2) resistance to beta-lactam antibiotics, with particular emphasis on the mec genes found in the Staphylococcaceae family, the structure and occurrence of SCCmec cassettes, as well as differences in the presence of some virulence genes and its expression in major epidemiological types and clones of HA-MRSA, CA-MRSA, and LA-MRSA strains. Other mechanisms of resistance to beta-lactam antibiotics will also be discussed, such as mutations in the gdpP gene, BORSA or MODSA phenotypes, as well as resistance to ceftobiprole and ceftaroline. (3) Resistance to glycopeptides (VRSA, VISA, hVISA strains, vancomycin tolerance). (4) Resistance to oxazolidinones (mutational and enzymatic resistance to linezolid). (5) Resistance to MLS-B (macrolides, lincosamides, ketolides, and streptogramin B). (6) Aminoglycosides and spectinomicin, including resistance genes, their regulation and localization (plasmids, transposons, class I integrons, SCCmec), and types and spectrum of enzymes that inactivate aminoglycosides. (7). Fluoroquinolones (8) Tetracyclines, including the mechanisms of active protection of the drug target site and active efflux of the drug from the bacterial cell. (9) Mupirocin. (10) Fusidic acid. (11) Daptomycin. (12) Resistance to other antibiotics and chemioterapeutics (e.g., streptogramins A, quinupristin/dalfopristin, chloramphenicol, rifampicin, fosfomycin, trimethoprim) (13) Molecular epidemiology of MRSA.

Efficacy of antimicrobial peptide LL-37 against biofilm forming Staphylococcus aureus strains obtained from chronic wound infections

The antimicrobial peptide LL-37 showed inhibitory effects against Staphylococcus aureus strains, which often responsible for wound infections. Understanding the molecular mechanisms of biofilm-containing wound infections is important. Thus, this study aimed to investigate both the antimicrobial and biofilm efficacy of LL-37 against biofilm-positive methicillin-susceptible S. aureus (MSSA) strains and biofilm-positive methicillin-resistant S. aureus (MRSA) strains obtained from chronic wound infections and its effect on different quorum sensing and virulence genes at suboptimal concentrations. Fifteen biofilm-forming MRSA and 15 biofilm-forming MSSA strains were included in this study. The minimum inhibitory concentration (MIC) values and biofilm formation were tested by microdilution methods. Real-time PCR was performed to determine gene expression levels. MIC values for LL-37 were 89.6 mg/L and 132.3 mg/L for MSSA and MRSA strains, respectively. No statistically significant difference was found between MRSA and MSSA strains in terms of the effect of LL-37 on biofilm formation. A statistically significant difference was found between MRSA and MSSA strains for atlA, RNAIII, and agrA gene expression levels following exposure to a suboptimal concentration of LL-37. Ultimately, the required LL-37 antimicrobial concentration was quite high; however, LL-37 antibiofilm concentration may be acceptable for use in humans against biofilm-forming MRSA and MSSA strains. This is the first study to investigate to effect of a suboptimal LL-37 concentration on gene expression levels of biofilm-forming MSSA and MRSA strains. LL-37 affected quorum sensing and biofilm producing mechanisms, even at suboptimal MIC concentrations.

Metabolic Adaptations During Staphylococcus aureus and Candida albicans Co-Infection

Successful pathogens require metabolic flexibility to adapt to diverse host niches. The presence of co-infecting or commensal microorganisms at a given infection site can further influence the metabolic processes required for a pathogen to cause disease. The Gram-positive bacterium Staphylococcus aureus and the polymorphic fungus Candida albicans are microorganisms that asymptomatically colonize healthy individuals but can also cause superficial infections or severe invasive disease. Due to many shared host niches, S. aureus and C. albicans are frequently co-isolated from mixed fungal-bacterial infections. S. aureus and C. albicans co-infection alters microbial metabolism relative to infection with either organism alone. Metabolic changes during co-infection regulate virulence, such as enhancing toxin production in S. aureus or contributing to morphogenesis and cell wall remodeling in C. albicans. C. albicans and S. aureus also form polymicrobial biofilms, which have greater biomass and reduced susceptibility to antimicrobials relative to mono-microbial biofilms. The S. aureus and C. albicans metabolic programs induced during co-infection impact interactions with host immune cells, resulting in greater microbial survival and immune evasion. Conversely, innate immune cell sensing of S. aureus and C. albicans triggers metabolic changes in the host cells that result in an altered immune response to secondary infections. In this review article, we discuss the metabolic programs that govern host-pathogen interactions during S. aureus and C. albicans co-infection. Understanding C. albicans-S. aureus interactions may highlight more general principles of how polymicrobial interactions, particularly fungal-bacterial interactions, shape the outcome of infectious disease. We focus on how co-infection alters microbial metabolism to enhance virulence and how infection-induced changes to host cell metabolism can impact a secondary infection.

Staphylococcus aureus infections in children

PURPOSE OF REVIEW

Staphylococcus aureus is the most common invasive bacterial pathogen infecting children in the U.S. and many parts of the world. This major human pathogen continues to evolve, and recognition of recent trends in epidemiology, therapeutics and future horizons is of high importance.

RECENT FINDINGS

Over the past decade, a relative rise of methicillin-susceptible S. aureus (MSSA) has occurred, such that methicillin-resistant S. aureus (MRSA) no longer dominates the landscape of invasive disease. Antimicrobial resistance continues to develop, however, and novel therapeutics or preventive modalities are urgently needed. Unfortunately, several recent vaccine attempts proved unsuccessful in humans.

SUMMARY

Recent scientific breakthroughs highlight the opportunity for novel interventions against S. aureus by interfering with virulence rather than by traditional antimicrobial mechanisms. A S. aureus vaccine remains elusive; the reasons for this are multifactorial, and lessons learned from prior unsuccessful attempts may create a path toward an effective preventive. Finally, new diagnostic modalities have the potential to greatly enhance clinical care for invasive S. aureus disease in children.

Pyranoanthocyanins Interfering with the Quorum Sensing of Pseudomonas aeruginosa and Staphylococcus aureus

Bacterial quorum sensing (QS) is a cell-cell communication system that regulates several bacterial mechanisms, including the production of virulence factors and biofilm formation. Thus, targeting microbial QS is seen as a plausible alternative strategy to antibiotics, with potentiality to combat multidrug-resistant pathogens. Many phytochemicals with QS interference activity are currently being explored. Herein, an extract and a compound of bioinspired origin were tested for their ability to inhibit biofilm formation and interfere with the expression of QS-related genes in Pseudomonas aeruginosa and Staphylococcus aureus. The extract, a carboxypyranoanthocyanins red wine extract (carboxypyrano-ant extract), and the pure compound, carboxypyranocyanidin-3-O-glucoside (carboxypyCy-3-glc), did not cause a visible effect on the biofilm formation of the P. aeruginosa biofilms; however, both significantly affected the formation of biofilms by the S. aureus strains, as attested by the crystal violet assay and fluorescence microscopy. Both the extract and the pure compound significantly interfered with the expression of several QS-related genes in the P. aeruginosa and S. aureus biofilms, as per reverse transcription-quantitative polymerase chain reaction (RT-qPCR) results. Indeed, it was possible to conclude that these molecules interfere with QS at distinct stages and in a strain-specific manner. An extract with anti-QS properties could be advantageous because it is easily obtained and could have broad, antimicrobial therapeutic applications if included in topical formulations.

Staphylococcus aureus Toxins: Promoter or Handicap during Infection?

Staphylococcus aureus is an opportunistic and versatile pathogen that can cause several diseases, which range from acute and destructive, to chronic and difficult-to-treat infections [...].

Mechanisms of Antibiotic Failure During Staphylococcus aureus Osteomyelitis

Staphylococcus aureus is a highly successful Gram-positive pathogen capable of causing both superficial and invasive, life-threatening diseases. Of the invasive disease manifestations, osteomyelitis or infection of bone, is one of the most prevalent, with S. aureus serving as the most common etiologic agent. Treatment of osteomyelitis is arduous, and is made more difficult by the widespread emergence of antimicrobial resistant strains, the capacity of staphylococci to exhibit tolerance to antibiotics despite originating from a genetically susceptible background, and the significant bone remodeling and destruction that accompanies infection. As a result, there is a need for a better understanding of the factors that lead to antibiotic failure in invasive staphylococcal infections such as osteomyelitis. In this review article, we discuss the different non-resistance mechanisms of antibiotic failure in S. aureus. We focus on how bacterial niche and destructive tissue remodeling impact antibiotic efficacy, the significance of biofilm formation in promoting antibiotic tolerance and persister cell formation, metabolically quiescent small colony variants (SCVs), and potential antibiotic-protected reservoirs within the substructure of bone.