SigV Mediates Lysozyme Resistance in Enterococcus faecalis via RsiV and PgdA

An innovative Pickering W/O/W nanoemulsion co-encapsulating hydrophilic lysozyme and hydrophobic Perilla leaf oil for extending shelf life of fish products

A Pickering water-in-oil-in-water nanoemulsion co-encapsulating lysozyme (LYS) and Perilla leaf oil (PO) was prepared using whey protein isolate-tannin acid conjugated nanoparticles (WPI-TA NPs) as emulsifiers, called LYS-PO-NE, and subsequently analyzed. The nano size and multiple phases was confirmed based on the results of confocal laser scanning microscope, scanning electron microscope, and droplet size analysis. LYS-PO-NE had high encapsulation efficiencies of 89.36 % (PO) and 43.91 % (LYS) and both could be released at a slow and continuous rate. The PO addition increased the droplet size, and the LYS addition delayed the release of PO. LYS-PO-NE also showed good storage, pH, thermal, and salt stability, and an effective combined bactericidal activity of LYS and PO against spoilage bacteria. Furthermore, the results of chilled salmon storage experiments indicated that LYS-PO-NE could extend the shelf life of chilled salmon to at least 6 days, demonstrating the potential in the shelf life for fish products.

The role of site-2-proteases in bacteria: a review on physiology, virulence, and therapeutic potential

Site-2-proteases are a class of intramembrane proteases involved in regulated intramembrane proteolysis. Regulated intramembrane proteolysis is a highly conserved signaling mechanism that commonly involves sequential digestion of an anti-sigma factor by a site-1- and site-2-protease in response to external stimuli, resulting in an adaptive transcriptional response. Variation of this signaling cascade continues to emerge as the role of site-2-proteases in bacteria continues to be explored. Site-2-proteases are highly conserved among bacteria and play a key role in multiple processes, including iron uptake, stress response, and pheromone production. Additionally, an increasing number of site-2-proteases have been found to play a pivotal role in the virulence properties of multiple human pathogens, such as alginate production in Pseudomonas aeruginosa, toxin production in Vibrio cholerae, resistance to lysozyme in enterococci and antimicrobials in several Bacillus spp, and cell-envelope lipid composition in Mycobacterium tuberculosis. The prominent role of site-2-proteases in bacterial pathogenicity highlights the potential of site-2-proteases as novel targets for therapeutic intervention. In this review, we summarize the role of site-2-proteases in bacterial physiology and virulence, as well as evaluate the therapeutic potential of site-2-proteases.

Disruption of the tagF Orthologue in the epa Locus Variable Region of Enterococcus faecalis Causes Cell Surface Changes and Suppresses an eep-Dependent Lysozyme Resistance Phenotype

The disease-producing capacity of the opportunistic pathogen Enterococcus faecalis is enhanced by the ability of the bacterium to evade killing by antimicrobial agents. Survival of E. faecalis in the presence of the human antimicrobial enzyme lysozyme is mediated in part by the site 2 metalloprotease Eep; however, a complete model of enterococcal lysozyme resistance has not been elucidated. To better understand the molecular basis for lysozyme resistance in E. faecalis, we analyzed Δeep suppressor mutants that acquire resistance to lysozyme through mutation of the gene OG1RF_11713, a predicted teichoic acid biosynthesis-encoding gene located within the variable region of the enterococcal polysaccharide antigen (epa) locus. Sequence comparisons revealed that OG1RF_11713 is most similar to the cytidine-5'-diphosphate (CDP)-glycerol:poly-(glycerolphosphate)glycerophosphotransferase TagF from Staphylococcus epidermidis. Inactivation of OG1RF_11713 in both the wild-type and Δeep genetic backgrounds was sufficient to increase the resistance of E. faecalis OG1RF to lysozyme. Minimal amounts of N-acetylgalactosamine were detectable in cell wall carbohydrate extracts of OG1RF_11713 deletion mutants, and this was associated with a reduction in negative cell surface charge. Targeted disruption of OG1RF_11713 was also associated with increased susceptibility to the antibiotic polymyxin B and membrane-targeting detergents and decreased susceptibility to the lantibiotic nisin. This work implicates OG1RF_11713 as a major determinant of cell envelope integrity and provides further validation that lysozyme resistance is intrinsically linked to the modification of enterococcal cell wall polysaccharides. IMPORTANCE Enterococcus faecalis is a leading cause of health-care-associated infections for which there are limited treatment options. E. faecalis is resistant to several antibiotics and to high concentrations of the human antimicrobial enzyme lysozyme. The molecular mechanisms that mediate lysozyme resistance in E. faecalis are complex and remain incompletely characterized. This work demonstrates that a gene located within the variable region of the enterococcal polysaccharide antigen locus of E. faecalis strain OG1RF (OG1RF_11713), which is predicted to encode a component of the teichoic acid biosynthesis machinery, is part of the lysozyme resistance circuitry and is important for enterococcal cell wall integrity. These findings suggest that OG1RF_11713 is a potential target for new therapeutic strategies to combat enterococcal infections.

C-phycocyanin alleviated cisplatin-induced oxidative stress and inflammation via gut microbiota—metabolites axis in mice

C-phycocyanin is a natural protein extracted from Spirulina platensis. We aim to investigate the preventive effect of C-phycocyanin on cisplatin chemotherapy-induced oxidative damage and inflammation. The result showed that C-phycocyanin treatment reduced cisplatin-induced mortality and inflammation including decreased levels of serum IL6, kidney MCP1, and liver IL1β. Furthermore, C-phycocyanin also exerted antioxidant effects on mice, including increased GSH-Px, GGT, and GSH levels in the liver and increased CAT and SOD levels in the kidney. HepG2 cells experiments showed that C-phycocyanin exhibited none of the prevention effects on cisplatin injury. Faecalibaculum showed the greatest reduction among genera after cisplatin treatment, which was related to the enrichment of Romboutsia and Lactobacillus genera. C-phycocyanin treatment reduced the populations of harmful bacteria of Enterococcus faecalis, which was positively correlated with inflammation induced by cisplatin. C-phycocyanin increased the contents of 23-nordeoxycholic acid and β-muricholic acid. Moreover, C-phycocyanin increased amino acid-related metabolites, Nα-acetyl-arginine and trimethyl-lysine contents, and decreased fatty acid esters of hydroxy fatty acids (FAHFAs) contents. In conclusion, C-phycocyanin inhibited inflammation via the 23-nordeoxycholic acid-Enterococcus faecalis-inflammation axis, and enhanced the antioxidant capacity of kidney via Lactobacillus-NRF2 pathway. C-phycocyanin alleviated cisplatin injury via the modulation of gut microbiota, especially Lactobacillus and Enterococcus, as well as regulation of metabolites, especially bile acid and FAHFAs, which highlight the effect of C-phycocyanin and provide a new strategy to prevent cisplatin injury.

Activation of the Extracytoplasmic Function σ Factor σV in Clostridioides difficile Requires Regulated Intramembrane Proteolysis of the Anti-σ Factor RsiV

Clostridioides (Clostridium) difficile is one of the leading causes of nosocomial diarrhea. Lysozyme is a common host defense against many pathogenic bacteria. C. difficile exhibits high levels of lysozyme resistance, which is due in part to the extracytoplasmic functioning (ECF) σ factor, σ^V. It has been previously demonstrated that genes regulated by σ^V are responsible for peptidoglycan modifications that provide C. difficile with high lysozyme resistance. σ^V is not unique to C. difficile however, and its role in lysozyme resistance and its mechanism of activation has been well characterized in Bacillus subtilis where the anti-σ, RsiV, sequesters σ^V until lysozyme directly binds to RsiV, activating σ^V. However, it remains unclear if the mechanism of σ^V activation is similar in C. difficile. Here, we investigated how activation of σ^V is controlled in C. difficile by lysozyme. We found that C. difficile RsiV was degraded in the presence of lysozyme. We also found that disruption of a predicted signal peptidase cleavage site blocked RsiV degradation and σ^V activation, indicating that the site-1 protease is likely a signal peptidase. We also identified a conserved site-2 protease, RasP, that was required for site-2 cleavage of RsiV and σ^V activation in response to lysozyme. Combined with previous work showing RsiV directly binds lysozyme, these data suggested that RsiV directly binds lysozyme in C. difficile, which leads to RsiV destruction via cleavage at site-1 by signal peptidase and then at site-2 by RasP, ultimately resulting in σ^V activation and increased resistance to lysozyme. IMPORTANCE Clostridioides difficile is a major cause of hospital-acquired diarrhea and represents an urgent concern due to the prevalence of antibiotic resistance and the rate of recurrent infections. We previously showed that σ^V and the regulon under its control were involved in lysozyme resistance. We have also shown in B. subtilis that the anti-σ RsiV acts as a direct sensor for lysozyme. which results in the destruction of RsiV and activation of σ^V. Here, we described the proteases required for degradation of RsiV in C. difficile in response to lysozyme. Our data indicated that the mechanism is highly conserved between B. subtilis and C. difficile.

The Cationic Antimicrobial Peptide Activity of Lysozyme Reduces Viable Enterococcus faecalis Cells in Biofilms

Enterococcus faecalis, a leading cause of health care-associated infections, forms biofilms and is resistant to many antimicrobial agents. Planktonic-phase E. faecalis is resistant to high concentrations of the enzyme lysozyme, which catalyzes the hydrolysis of N-acetylmuramic acid and N-acetylglucosamine linkages in peptidoglycan and is also a cationic antimicrobial peptide (CAMP). E. faecalis lysozyme resistance in planktonic cells is stimulated upon activation of the extracytoplasmic function sigma factor SigV via cleavage of the anti-sigma factor RsiV by the transmembrane protease Eep. Planktonically grown E. faecalis lacking eep is more sensitive than wild-type strains to growth inhibition by lysozyme. This study was initiated to determine whether E. faecalis OG1RFΔeep biofilms would be protected from lysozyme. Serendipitously, we discovered that exposure of both E. faecalis OG1RF and OG1RFΔeep biofilms to chicken egg white lysozyme resulted in decreases in biofilm cell viability of 3.7 and 3.8 log₁₀ CFU/mL, respectively. Treatment of biofilms of both strains with recombinant purified human lysozyme was associated with reductions in cell viability of >99.9% for both strains. Lysozyme-treated OG1RF and OG1RFΔeep biofilms contained a higher percentage of dead cells by Live/Dead staining and were associated with more extracellular DNA. Heat-inactivated human lysozyme, which was devoid of muramidase activity, as well as the lysozyme-derived CAMP LP9 and the CAMP polymyxin B, decreased biofilm cell viability. These results are consistent with a model in which the CAMP activity, rather than the muramidase activity, of lysozyme causes lysis of E. faecalis biofilm cells despite them having an intact lysozyme resistance-inducing signaling pathway. Finally, lysozyme was also effective in reducing viable biofilm cells of several other E. faecalis strains, including the vancomycin-resistant strain V583 and multidrug-resistant strain MMH594. This study demonstrates the potential for lysozyme to be developed as a novel antibiofilm therapeutic.

Activation of the extracytoplasmic function σ factor σV by lysozyme in Clostridioides difficile

Clostridioides difficile is naturally resistant to high levels of lysozyme an important component of the innate immune defense system. C. difficile encodes both constitutive as well as inducible lysozyme resistance genes. The inducible lysozyme resistance genes are controlled by an alternative σ factor σ^V that belongs to the Extracytoplasmic function σ factor family. In the absence of lysozyme, the activity of σ^V is inhibited by the anti-σ factor RsiV. In the presence of lysozyme RsiV is destroyed via a proteolytic cascade that leads to σ^V activation and increased lysozyme resistance. This review highlights how activity of σ^V is controlled.

Signal Peptidase-Mediated Cleavage of the Anti-σ Factor RsiP at Site 1 Controls σP Activation and β-Lactam Resistance in Bacillus thuringiensis

In Bacillus thuringiensis, β-lactam antibiotic resistance is controlled by the extracytoplasmic function (ECF) σ factor σ^P. σ^P activity is inhibited by the anti-σ factor RsiP. In the presence of β-lactam antibiotics, RsiP is degraded and σ^P is activated. Previous work found that RsiP degradation requires cleavage of RsiP at site 1 by an unknown protease, followed by cleavage at site 2 by the site 2 protease RasP. The penicillin-binding protein PbpP acts as a sensor for β-lactams. PbpP initiates σ^P activation and is required for site 1 cleavage of RsiP but is not the site 1 protease. Here, we describe the identification of a signal peptidase, SipP, which cleaves RsiP at a site 1 signal peptidase cleavage site and is required for σ^P activation. Finally, many B. anthracis strains are sensitive to β-lactams yet encode the σ^P-RsiP signal transduction system. We identified a naturally occurring mutation in the signal peptidase cleavage site of B. anthracis RsiP that renders it resistant to SipP cleavage. We find that B. anthracis RsiP is not degraded in the presence of β-lactams. Altering the B. anthracis RsiP site 1 cleavage site by a single residue to resemble B. thuringiensis RsiP results in β-lactam-dependent degradation of RsiP. We show that mutation of the B. thuringiensis RsiP cleavage site to resemble the sequence of B. anthracis RsiP blocks degradation by SipP. The change in the cleavage site likely explains many reasons why B. anthracis strains are sensitive to β-lactams. IMPORTANCE β-Lactam antibiotics are important for the treatment of many bacterial infections. However, resistance mechanisms have become increasingly more prevalent. Understanding how β-lactam resistance is conferred and how bacteria control expression of β-lactam resistance is important for informing the future treatment of bacterial infections. σ^P is an alternative σ factor that controls the transcription of genes that confer β-lactam resistance in Bacillus thuringiensis, Bacillus cereus, and Bacillus anthracis. Here, we identify a signal peptidase as the protease required for initiating activation of σ^P by the degradation of the anti-σ factor RsiP. The discovery that the signal peptidase SipP is required for σ^P activation highlights an increasing role for signal peptidases in signal transduction, as well as in antibiotic resistance.