Innate and adaptive immune responses against Staphylococcus aureus skin infections

Double positive IL-17A+IFN-γ+CCR6+ ILCs contribute towards the immunopathology of lepromatous leprosy

Leprosy is a skin disease caused by Mycobacterium leprae, characterized by both localized and generalized immune responses. Th1/17 lymphocytes play a crucial role in the immune response against M. leprae. However, adaptive immunity alone is not sufficient to completely eradicate the pathogen, suggesting the involvement of other innate immune cells in pathogen removal. Therefore, we investigated innate lymphoid cells (ILCs), which are the innate counterparts of helper T cells in adaptive immunity and are known to produce IFN-γ and IL-17. In the present study, we evaluated the expression of ILC1 and ILC3 in borderline tuberculoid (BT) and lepromatous leprosy (LL) lesional skin by flow cytometry and real time PCR. Further, the expression of various in-situ genes, including cytokines, chemokines, cytokine receptors chemokine receptors, and transcription factors by qPCR in skin lesions of leprosy patients were analyzed. The phenotypes of ILC1 and ILC3 cells were determined as CD3negCCR6+CD19negIFN-γ+ and CD3negCCR6+CD19negIL-17A+, respectively, by flow-cytometry analysis. BT skin lesions represents high CCR6+expression on total ILCs as compared to LL patients. Our results clearly indicate that ILC1 and ILC3 were highly expressed in skin lesions of BT as compared to LL leprosy patients. Moreover, we observed that double positive (DP) CD3negCCR6+CD19negIFN-γ+IL-17A+ ILCs were up-regulated in LL and showed a pathogenic role. The gene expression of IL-17A and IFN-γ were found to be significantly positively correlated with the percentage of CCR6+ ILCs. On the other hand, CCR6neg ILCs were negatively correlated with ILC1 and ILC3 associated markers. Summarily our results clearly suggest that both ILC1 and ILC3 are important and immune-protective, on the contrary DP (IFN-γ+IL-17A+) ILCs may promote progression and immunopathology of leprosy.

Clinical Features and Antibiotic Susceptibility of Staphylococcus aureus-Infected Dermatoses

Background/Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) poses significant treatment challenges, particularly in community settings. Limited data are available on S. aureus-associated infected dermatoses (ID) in outpatient dermatology clinics. This study examines the clinical characteristics, microbiological profiles, resistance patterns, and treatment outcomes of dermatoses caused by S. aureus. Methods: Between January 2023 and January 2025, consecutive patients with confirmed S. aureus-associated SD were recruited in a dermatology clinic in Heraklion, Greece. Demographic, clinical, and treatment data were collected. Skin swabs underwent bacterial culture and antimicrobial susceptibility testing following CLSI guidelines. Statistical analyses evaluated associations between clinical and microbiological findings. Results: Sixty-eight patients were included, 54.4% of whom were male, with a mean age of 46.7 years (± SD 25.1). MRSA was identified in 22.1% of cases and was significantly associated with female gender (p = 0.014). The most common diagnoses were eczema (35.3%) and folliculitis (19.1%). Oxacillin-resistant patients were more likely to receive systemic therapy (p = 0.039). Resistance rates were highest for benzylpenicillin (81.8%), levofloxacin (54.9%), and erythromycin (39.4%). Resistance rates for fusidic acid, clindamycin, mupirocin, and tetracycline were 38.2%, 20.6%, 16.9%, and 10.3%, respectively. Other pathogens, including Pseudomonas aeruginosa and Escherichia coli, were isolated in 27.9% of cases. Conclusions: This study highlights the high prevalence of MRSA in outpatient dermatology settings, emphasizing the need for local antimicrobial resistance surveillance to guide treatment strategies and improve outcomes in superinfected dermatoses.

Staphyloccocus aureus biofilm, in absence of planktonic bacteria, produces factors that activate counterbalancing inflammatory and immune-suppressive genes in human monocytes

Staphyloccocus aureus (S. aureus) is a major bacterial pathogen in orthopedic periprosthetic joint infection (PJI). S. aureus forms biofilms that promote persistent infection by shielding bacteria from immune cells and inducing an antibiotic-tolerant metabolic state. We developed an in vitro system to study S. aureus biofilm interactions with primary human monocytes in the absence of planktonic bacteria. In line with previous in vivo data, S. aureus biofilm induced expression of inflammatory genes such as TNF and IL1B, and their anti-inflammatory counter-regulator IL10. S. aureus biofilm also activated expression of PD-1 ligands, and IL-1RA, molecules that have the potential to suppress T cell function or differentiation of protective Th17 cells. Gene induction did not require monocyte:biofilm contact and was mediated by a soluble factor(s) produced by biofilm-encased bacteria that was heat resistant and >3 kD in size. Activation of suppressive genes by biofilm was sensitive to suppression by Jak kinase inhibition. These results support an evolving paradigm that biofilm plays an active role in modulating immune responses, and suggest this occurs via production of a soluble vita-pathogen-associated molecular pattern, a molecule that signals microbial viability. Induction of T cell suppressive genes by S. aureus biofilm provides insights into mechanisms that can suppress T cell immunity in PJI.

Absence of Langerhans cells resulted in over-influx of neutrophils and increased bacterial burden in skin wounds

Langerhans cells (LCs) are resident dendritic cells in the epidermis and their roles in presenting antigens derived from microorganisms present in the skin has been well appreciated. However, it is generally thought that incoming neutrophils are mainly responsible for eradicating invading pathogens in the early stage of wounds and a role of LCs in innate immunity is elusive. In the current study, we showed that wounds absent of LCs had a delayed closure. Mechanistically, LCs were the primary cells in warding off bacteria invasion at the early stage of wound healing. Without LCs, commensal bacteria quickly invaded and propagated in the wounded area. keratinocytes surrounding the wounds responded to the excessive bacteria by elevated production of CXCL5, resulting in an over-influx of neutrophils. The over-presence of activated neutrophils, possibly together with the aggravated invasion of bacteria, was detrimental to epidermal progenitor cell propagation and re-epithelialization. These observations underscore an indispensable role of LCs as effective guardians that preclude both bacteria invasion and damages inflicted by secondary inflammation.

In Vitro Anti-inflammatory Effects of Larch Turpentine, Turpentine Oil, Eucalyptus Oil, and Their Mixture as Contained in a Marketed Ointment

An ointment containing larch turpentine, turpentine oil, and eucalyptus oil has been used for almost a century for the symptomatic treatment of mild, localized, purulent inflammations of the skin. Its clinical efficacy in the treatment of skin infections has been shown in clinical trials, but the mode of action of the active ingredients on inflammation is not known. We studied the anti-inflammatory properties of the active ingredients of the ointment and their mixture in a human monocyte cell model, in which the cells were stimulated with lipopolysaccharide and incubated with the test substances. The cytotoxic threshold of each test substance and the mixture was identified using the alamarBlue assay, and their anti-inflammatory activity was assessed by measuring the release of interleukins IL-1β, IL-6, IL-8, monocyte chemoattractant protein-1, prostaglandin E2, and TNF-α. Cell toxicity was observed at a mixture concentration of 10 µg/mL. All immunological assays were carried out at nontoxic concentrations. Larch turpentine decreased IL-1β, monocyte chemoattractant protein-1, and prostaglandin E2 release at a concentration of 3.9 µg/mL and TNF-α at concentrations > 1.95 µg/mL, whereas eucalyptus oil and turpentine oil had no relevant inhibitory effects. The mixture dose-dependently inhibited IL-1β, IL-6, monocyte chemoattractant protein-1, prostaglandin E2, and TNF-α release at concentrations > 1 µg/mL. IL-8 release was only marginally affected. The anti-inflammatory activity of the herbal ingredients and their mixture was confirmed in this model. This effect seems to be mediated mainly by larch turpentine, with turpentine oil and eucalyptus oil exerting an additive or possibly synergistic function.

LECs regulate neutrophil clearance through IL-17RC/CMTM4/NF-κB axis at sites of inflammation or infection

The lymphatic system plays a vital role in the regulation of tissue fluid balance and the immune response to inflammation or infection. The effects of lymphatic endothelial cells (LECs) on the regulation of neutrophil migration have not been well-studied. In three murine models: imiquimod-induced skin inflammation, Staphylococcus aureus-induced skin infection, and ligature-induced periodontitis, we show that numerous neutrophils migrate from inflamed or infected tissues to the draining lymph nodes via lymphatic vessels. Moreover, inflamed or infected tissues express a high level of interleukin (IL)-17A and tumor necrosis factor (TNF)-α, simultaneously with a significant increase in the release of neutrophil attractors, including CXCL1, CXCL2, CXCL3, and CXCL5. Importantly, in vitro stimulation of LECs with IL-17A plus TNF-α synergistically promoted these chemokine secretions. Mechanistically, tetra-transmembrane protein CMTM4 directly binds to IL-17RC in LECs. IL-17A plus TNF-α stimulates CXC chemokine secretion by promoting nuclear factor-kappa B signaling. In contrast, knockdown of CMTM4 abrogates IL-17A plus TNF-α activated nuclear factor-kappa B signaling pathways. Lastly, the local administration of adeno-associated virus for CMTM4 in Prox1-CreERT2 mice, mediating LEC-specific overexpression of CMTM4, promotes the drainage of neutrophils by LECs and alleviates immune pathological responses. Thus, our findings reveal the vital role of LECs-mediated neutrophil attraction and clearance at sites of inflammation or infection.

Unveiling the mechanism of essential oil action against skin pathogens: from ancient wisdom to modern science

Essential oils are among the most well-known phyto-compounds, and since ancient times, they have been utilized in medicine. Over 100 essential oils have been identified and utilized as therapies for various skin infections and related ailments. While numerous commercial medicines are available in different dosage forms to treat skin diseases, the persisting issues include their side effects, toxicity, and low efficacy. As a result, researchers are seeking novel classes of compounds as substitutes for synthetic drugs, aiming for minimal side effects, no toxicity, and high efficacy. Essential oils have shown promising antimicrobial activity against skin-associated pathogens. This review presents essential knowledge and scientific information regarding essential oil's antimicrobial capabilities against microorganisms that cause skin infections. Essential oils mechanisms against different pathogens have also been explored. Many essential oils exhibit promising activity against various microbes, which has been qualitatively assessed using the agar disc diffusion experiment, followed by determining the minimum inhibitory concentration for quantitative evaluation. It has been observed that Staphylococcus aureus and Candida albicans have been extensively researched in the context of skin-related infections and their antimicrobial activity, including established modes of action. In contrast, other skin pathogens such as Staphylococcus epidermidis, Streptococcus pyogens, Propionibacterium acnes, and Malassezia furfur have received less attention or neglected. This review report provides an updated understanding of the mechanisms of action of various essential oils with antimicrobial properties. This review explores the anti-infectious activity and mode of action of essential against distinct skin pathogens. Such knowledge can be valuable in treating skin infections and related ailments.

IL-10 inhibition during immunization improves vaccine-induced protection against Staphylococcus aureus infection

Staphylococcus aureus is a major human pathogen. An effective anti-S. aureus vaccine remains elusive as the correlates of protection are ill-defined. Targeting specific T cell populations is an important strategy for improving anti-S. aureus vaccine efficacy. Potential bottlenecks that remain are S. aureus-induced immunosuppression and the impact this might have on vaccine-induced immunity. S. aureus induces IL-10, which impedes effector T cell responses, facilitating persistence during both colonization and infection. Thus, it was hypothesized that transient targeting of IL-10 might represent an innovative way to improve vaccine efficacy. In this study, IL-10 expression was elevated in the nares of persistent carriers of S. aureus, and this was associated with reduced systemic S. aureus-specific Th1 responses. This suggests that systemic responses are remodeled because of commensal exposure to S. aureus, which negatively implicates vaccine function. To provide proof of concept that targeting immunosuppressive responses during immunization may be a useful approach to improve vaccine efficacy, we immunized mice with T cell-activating vaccines in combination with IL-10-neutralizing antibodies. Blocking IL-10 during vaccination enhanced effector T cell responses and improved bacterial clearance during subsequent systemic and subcutaneous infection. Taken together, these results reveal a potentially novel strategy for improving anti-S. aureus vaccine efficacy.

Immune cells in skin inflammation, wound healing, and skin cancer

Given the self-evident importance of cutaneous immunity in the maintenance of body-surface homeostasis, disturbance of the steady-state skin is inextricably intertwined with dysfunction in cutaneous immunity. It is often overlooked by people that skin, well-known as a solid physical barrier, is also a strong immunological barrier, considering the abundant presence of immune cells including lymphocytes, granulocytes, dendritic cells, and macrophages. What's more, humoral immune components including cytokines, immunoglobulins, and antimicrobial peptides are also rich in the skin. This review centers on skin inflammation (acute and chronic, infection and aseptic inflammation), wound healing, and skin cancer to elucidate the elaborate network of immune cells in skin diseases.

Staphylococcus aureus Infections and Human Intestinal Microbiota

Staphylococcus aureus (S. aureus) is a common pathogen that can cause many human diseases, such as skin infection, food poisoning, endocarditis, and sepsis. These diseases can be minor infections or life-threatening, requiring complex medical management resulting in substantial healthcare costs. Meanwhile, as the critically ignored "organ," the intestinal microbiome greatly impacts physiological health, not only in gastrointestinal diseases but also in disorders beyond the gut. However, the correlation between S. aureus infection and intestinal microbial homeostasis is largely unknown. Here, we summarized the recent progress in understanding S. aureus infections and their interactions with the microbiome in the intestine. These summarizations will help us understand the mechanisms behind these infections and crosstalk and the challenges we are facing now, which could contribute to preventing S. aureus infections, effective treatment investigation, and vaccine development.

Novel small-molecule compound YH7 inhibits the biofilm formation of Staphylococcus aureus in a sarX-dependent manner

The emergence of antibiotic-resistant and biofilm-producing Staphylococcus aureus isolates presents major challenges for treating staphylococcal infections. Biofilm inhibition is an important anti-virulence strategy. In this study, a novel maleimide-diselenide hybrid compound (YH7) was synthesized and demonstrated remarkable antimicrobial activity against methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) in both planktonic cultures and biofilms. The minimum inhibitory concentration (MIC) of YH7 for S. aureus isolates was 16 µg/mL. Quantification of biofilms demonstrated that the sub-MIC (4 µg/mL) of YH7 significantly inhibits biofilm formation in both MSSA and MRSA. Confocal laser scanning microscopy analysis further confirmed the biofilm inhibitory potential of YH7. YH7 also significantly suppressed bacterial adherence to A549 cells. Moreover, YH7 treatment significantly inhibited S. aureus colonization in nasal tissue of mice. Preliminary mechanistic studies revealed that YH7 exerted potent biofilm-suppressing effects by inhibiting polysaccharide intercellular adhesin (PIA) synthesis, rather than suppressing bacterial autolysis. Real-time quantitative PCR data indicated that YH7 downregulated biofilm formation-related genes (clfA, fnbA, icaA, and icaD) and the global regulatory gene sarX, which promotes PIA synthesis. The sarX-dependent antibiofilm potential of YH7 was validated by constructing S. aureus NCTC8325 sarX knockout and complementation strains. Importantly, YH7 demonstrated a low potential to induce drug resistance in S. aureus and exhibited non-toxic to rabbit erythrocytes, A549, and BEAS-2B cells at antibacterial concentrations. In vivo toxicity assays conducted on Galleria mellonella further confirmed that YH7 is biocompatible. Overall, YH7 demonstrated potent antibiofilm activity supports its potential as an antimicrobial agent against S. aureus biofilm-related infections. IMPORTANCE Biofilm-associated infections, characterized by antibiotic resistance and persistence, present a formidable challenge in healthcare. Traditional antibacterial agents prove inadequate against biofilms. In this study, the novel compound YH7 demonstrates potent antibiofilm properties by impeding the adhesion and the polysaccharide intercellular adhesin production of Staphylococcus aureus. Notably, its exceptional efficacy against both methicillin-resistant and methicillin-susceptible strains highlights its broad applicability. This study highlights the potential of YH7 as a novel therapeutic agent to address the pressing issue of biofilm-driven infections.

Increased S. aureus colonization and reduced antimicrobial peptide expression in erythrodermic psoriasis

BACKGROUND

Erythrodermic psoriasis (EP) is a severe and rare condition characterized by prominent erythema and scaling over 75 % of the body surface area. Unlike psoriasis vulgaris (PV), EP carries high risk of systemic involvement, including superficial skin infections and sepsis, particularly those caused by Staphylococcus aureus.

OBJECTIVE

To explore the microecological characteristics of EP and detect the levels of antimicrobial peptides (AMPs) in both skin and serum of EP patients.

METHODS

In this study, skin microbiomes of 10 EP patients were analyzed through 16S rRNA gene sequencing. The expressions of AMPs, Interleukin-4/13 (IL-4/13), Interleukin-17 (IL-17) and Interferon-γ (IFN-γ) in skin were detected via immunohistochemical staining and serum levels of AMP were evaluated by ELISA. We also enrolled 10 AD and 10 PV patients as controls.

RESULTS

EP patients retained rich microbial diversity, dominated by S. aureus. The AMPs of hBD2, LL-37, and RNase7 in EP keratinocytes were significantly lower than those in PV, but higher than those in AD. The expression levels of IL-4, IL-13 and IFN-γ in lesions are similar between EP and AD, but quite different from PV. What's more, the serum AMP levels in EP were similar to those in PV while significantly lower than in AD.

CONCLUSION

We found EP patients have a rich microbial diversity dominated by S. aureus in lesions, while lower serum and skin AMPs expressions, which may account for the increased incidence of S. aureus cutaneous infections and sepsis in EP patients.

Mammary γδ T cells promote IL-17A-mediated immunity against Staphylococcus aureus-induced mastitis in a microbiota-dependent manner

Mastitis, a common disease for female during lactation period that could cause a health risk for human or huge economic losses for animals, is mainly caused by S. aureus invasion. Here, we found that neutrophil recruitment via IL-17A-mediated signaling was required for host defense against S. aureus-induced mastitis in a mouse model. The rapid accumulation and activation of Vγ4+ γδ T cells in the early stage of infection triggered the IL-17A-mediated immune response. Interestingly, the accumulation and influence of γδT17 cells in host defense against S. aureus-induced mastitis in a commensal microbiota-dependent manner. Overall, this study, focusing on γδT17 cells, clarified innate immune response mechanisms against S. aureus-induced mastitis, and provided a specific response to target for future immunotherapies. Meanwhile, a link between commensal microbiota community and host defense to S. aureus mammary gland infection may unveil potential therapeutic strategies to combat these intractable infections.

The secretome of Staphylococcus aureus strains with opposite within-herd epidemiological behavior affects bovine mononuclear cell response

Staphylococcus aureus modulates the host immune response directly by interacting with the immune cells or indirectly by secreting molecules (secretome). Relevant differences in virulence mechanisms have been reported for the secretome produced by different S. aureus strains. The present study investigated the S. aureus secretome impact on peripheral bovine mononuclear cells (PBMCs) by comparing two S. aureus strains with opposite epidemiological behavior, the genotype B (GTB)/sequence type (ST) 8, associated with a high within-herd prevalence, and GTS/ST398, associated with a low within-herd prevalence. PBMCs were incubated with different concentrations (0%, 0.5%, 1%, and 2.5%) of GTB/ST8 and GTS/ST398 secretome for 18 and 48 h, and the viability was assessed. The mRNA levels of pro- (IL1-β and STAT1) and anti-inflammatory (IL-10, STAT6, and TGF-β) genes, and the amount of pro- (miR-155-5p and miR-125b-5p) and anti-inflammatory (miR-146a and miR-145) miRNAs were quantified by RT-qPCR. Results showed that incubation with 2.5% of GTB/ST8 secretome increased the viability of cells. In contrast, incubation with the GTS/ST398 secretome strongly decreased cell viability, preventing any further assays. The GTB/ST8 secretome promoted PBMC polarization towards the pro-inflammatory phenotype inducing the overexpression of IL1-β, STAT1 and miR-155-5p, while the expression of genes involved in the anti-inflammatory response was not affected. In conclusion, the challenge of PBMC to the GTS/ST398 secretome strongly impaired cell viability, while exposure to the GTB/ST8 secretome increased cell viability and enhanced a pro-inflammatory response, further highlighting the different effects exerted on host cells by S. aureus strains with epidemiologically divergent behaviors.

Detection and characterization of potential virulence determinants in Staphylococcus pseudintermedius and S. schleiferi strains isolated from canine otitis externa in Korea

BACKGROUND

A recent increase in the occurrence of canine skin and soft tissue infections, including otitis externa and pyoderma, caused by antimicrobial-resistant Staphylococcus pseudintermedius and S. schleiferi has become a significant public and veterinary health issues.

OBJECTIVE

We investigated the virulence potentials associated with the occurrence of canine otitis externa in S. pseudintermedius and S. schleiferi.

METHODS

In this study, the prevalence of genes encoding leukocidins, exfoliative toxins, and staphylococcal enterotoxins (SEs) was investigated using previously characterized S. pseudintermedius (n = 26) and S. schleiferi (n = 19) isolates derived from canine otitis externa. Susceptibility to cathelicidins (K9CATH and PMAP-36) and hydrogen peroxide (H2O2) was also examined in both staphylococcal species.

RESULTS

A high prevalence of genes encoding leukocidins (lukS/F-I, lukS1/F1-S, and lukS2/F2-S), exfoliative toxins (siet, expB, and sset), and SEs was identified in both S. pseudintermedius and S. schleiferi isolates. Notably, S. pseudintermedius isolates possessed higher number of SE genes, especially newer SE genes, than S. schleiferi isolates harboring egc clusters. Although no significant differences in susceptibility to K9CATH and H2O2 were observed between the two isolate groups, S. pseudintermedius isolates exhibited enhanced resistance to PMAP-36 compared to S. schleiferi isolates.

CONCLUSIONS

These findings suggest that high a prevalence of various toxin genes together with enhanced resistance to cathelicidins may contribute to the pathogenicity of S. pseudintermedius and S. schleiferi in canine cutaneous infections.

Antigen specific activation of cytotoxic CD8+ T cells by Staphylococcus aureus infected dendritic cells

Staphylococcus aureus (S. aureus) is a pathogen associated with a wide variety of diseases, from minor to life-threatening infections. Antibiotic-resistant strains have emerged, leading to increasing concern about the control of S. aureus infections. The development of vaccines may be one way to overcome these resistant strains. However, S. aureus ability to internalize into cells - and thus to form a reservoir escaping humoral immunity - is a challenge for vaccine development. A role of T cells in the elimination of persistent S. aureus has been established in mice but it remains to be established if CD8+ T cells could display a cytotoxic activity against S. aureus infected cells. We examined in vitro the ability of CD8+ T cells to recognize and kill dendritic cells infected with S. aureus. We first evidenced that both primary mouse dendritic cells and DC2.4 cell line can be infected with S. aureus. We then generated a strain of S. aureus expressing a model CD8 epitope and transgenic F5 CD8+ T cells recognizing this model epitope were used as reporter T cells. In response to S. aureus-infected dendritic cells, F5 CD8+ T cells produced IFN-γ in an antigen-specific manner and displayed an increased ability to kill infected cells. Altogether, these results demonstrate that cells infected by S. aureus display bacteria-derived epitopes at their surface that are recognized by CD8+ T cells. This paves the way for the development of CD8+ T cell-based therapies against S. aureus.

The Sympathetic Nervous System Is Necessary for Development of CD4+ T-Cell Memory Following Staphylococcus aureus Infection

Lymph nodes and spleens are innervated by sympathetic nerve fibers that enter alongside arteries. Despite discovery of these nerve fibers nearly 40 years ago, the role of these nerves during response to infection remains poorly defined. We have found that chemical depletion of sympathetic nerve fibers compromises the ability of mice to develop protective immune memory to a Staphylococcus aureus infection. Innate control of the primary infection was not impacted by sympathectomy. Germinal center formation is also compromised in nerve-depleted animals; however, protective antibody responses are still generated. Interestingly, protective CD4+ T-cell memory fails to form in the absence of sympathetic nerves after S aureus infection.

The effect of Staphylococcus aureus on innate and adaptive immunity and potential immunotherapy for S. aureus-induced osteomyelitis

Osteomyelitis is a chronic inflammatory bone disease caused by infection of open fractures or post-operative implants. Particularly in patients with open fractures, the risk of osteomyelitis is greatly increased as the soft tissue damage and bacterial infection are often more severe. Staphylococcus aureus, one of the most common pathogens of osteomyelitis, disrupts the immune response through multiple mechanisms, such as biofilm formation, virulence factor secretion, and metabolic pattern alteration, which attenuates the effectiveness of antibiotics and surgical debridement toward osteomyelitis. In osteomyelitis, immune cells such as neutrophils, macrophages and T cells are activated in response to pathogenic bacteria invasion with excessive inflammatory factor secretion, immune checkpoint overexpression, and downregulation of immune pathway transcription factors, which enhances osteoclastogenesis and results in bone destruction. Therefore, the study of the mechanisms of abnormal immunity will be a new breakthrough in the treatment of osteomyelitis.

Nitrate Reductase NarGHJI Modulates Virulence via Regulation of agr Expression in Methicillin-Resistant Staphylococcus aureus Strain USA300 LAC

Staphylococcus aureus is a pathogenic bacterium with a widespread distribution that can cause diverse severe diseases. The membrane-bound nitrate reductase NarGHJI serves respiratory function. However, little is known about its contribution to virulence. In this study, we demonstrated that narGHJI disruption results in the downregulation of virulence genes (e.g., RNAIII, agrBDCA, hla, psmα, and psmβ) and reduces the hemolytic activity of the methicillin-resistant S. aureus (MRSA) strain USA300 LAC. Moreover, we provided evidence that NarGHJI participates in regulating host inflammatory response. A mouse model of subcutaneous abscess and Galleria mellonella survival assay demonstrated that the ΔnarG mutant was significantly less virulent than the wild type. Interestingly, NarGHJI contributes to virulence in an agr-dependent manner, and the role of NarGHJI differs between different S. aureus strains. Our study highlights the novel role of NarGHJI in regulating virulence, thereby providing a new theoretical reference for the prevention and control of S. aureus infection. IMPORTANCE Staphylococcus aureus is a notorious pathogen that poses a great threat to human health. The emergence of drug-resistant strains has significantly increased the difficulty of preventing and treating S. aureus infection and enhanced the pathogenic ability of the bacterium. This indicates the importance of identifying novel pathogenic factors and revealing the regulatory mechanisms through which they regulate virulence. The nitrate reductase NarGHJI is mainly involved in bacterial respiration and denitrification, which can enhance bacterial survival. We demonstrated that narGHJI disruption results in the downregulation of the agr system and agr-dependent virulence genes, suggesting that NarGHJI participates in the regulation of S. aureus virulence in an agr-dependent manner. Moreover, the regulatory approach is strain specific. This study provides a new theoretical reference for the prevention and control of S. aureus infection and reveals new targets for the development of therapeutic drugs.

Effects of cadmium and diethylhexyl phthalate on skin microbiota of Rana chinensis tadpoles

Skin microbiotas play a crucial role in the health, homeostasis, and immune function of amphibians. The contaminants in water could affect the structure and composition of microbial communities. The effects of coexisting pollutants on frogs cannot be adequately explained by a single exposure due to the coexistence of Cd and DEHP in the environment. Following exposure to Cd and/or DEHP, we examined the histological characteristics of Rana chensinensis tadpoles. We also used the 16S rRNA gene sequencing technique to assess the relative abundance of skin microbial communities among tadpoles from each treatment group. Our findings indicate that R. chensinensis' skin experienced some degree of injury due to exposure to Cd and DEHP, which led to the imbalance of their skin microbial community homeostasis and thus interfered with the normal trial status of the host. That may eventually lead to the decline of the amphibian population.

Turpentine Ointment in Bacterial Skin Infections: A Randomized, Placebo-Controlled, Double-Blind Clinical Trial

BACKGROUND

Turpentine-containing substances are considered effective in treating cutaneous bacterial infections, but reliable clinical data are scant.

OBJECTIVE

We investigated the efficacy and safety of an ointment containing larch turpentine (from Larix decidua), eucalyptus oil (from Eucalyptus globulus), and turpentine oil (from Pinus pinaster) in outpatients with painful skin abscesses in a randomized, placebo-controlled, double-blind study.

INTERVENTION

116 outpatients with skin abscesses used verum or placebo for 10 days. Sum score of the patient's discomforts, changes in abscess size, rate of therapeutic success, and complete healing served as outcome parameters.

RESULTS

Fifty-four patients were treated with verum and 56 with placebo. According to the patient's discomfort sum score, patients in the verum group showed a better improvement compared to the placebo group (7.3 vs. 4.7; p = 0.024), and subjective assessment by the investigators revealed a higher treatment success rate after verum (70% vs. 48%; p = 0.021). Complete healing was documented in 67% of the patients receiving verum versus 46% in the placebo group (p = 0.037). There was a positive trend toward a larger decrease in the abscess sizes in the verum group compared to the placebo group (p = 0.07).

CONCLUSION

The ointment studied is an effective and safe option for the treatment of bacterial skin diseases.

Staphylococcus aureus lipoproteins in infectious diseases

Infections with the Gram-positive bacterial pathogen Staphylococcus aureus remain a major challenge for the healthcare system and demand new treatment options. The increasing antibiotic resistance of S. aureus poses additional challenges, consequently inflicting a huge strain in the society due to enormous healthcare costs. S. aureus expresses multiple molecules, including bacterial lipoproteins (Lpps), which play a role not only in immune response but also in disease pathogenesis. S. aureus Lpps, the predominant ligands of TLR2, are important for bacterial survival as they maintain the metabolic activity of the bacteria. Moreover, Lpps possess many diverse properties that are of vital importance for the bacteria. They also contribute to host cell invasion but so far their role in different staphylococcal infections has not been fully defined. In this review, we summarize the current knowledge about S. aureus Lpps and their distinct roles in various infectious disease animal models, such as septic arthritis, sepsis, and skin and soft tissue infections. The molecular and cellular response of the host to S. aureus Lpp exposure is also a primary focus.

Identification and characterization of the pathogenic potential of phenol-soluble modulin toxins in the mouse commensal Staphylococcus xylosus

In contrast to the virulent human skin commensal Staphylococcus aureus, which secretes a plethora of toxins, other staphylococci have much reduced virulence. In these species, commonly the only toxins are those of the phenol-soluble modulin (PSM) family. PSMs are species-specific and have only been characterized in a limited number of species. S. xylosus is a usually innocuous commensal on the skin of mice and other mammals. Prompted by reports on the involvement of PSMs in atopic dermatitis (AD) and the isolation of S. xylosus from mice with AD-like symptoms, we here identified and characterized PSMs of S. xylosus with a focus on a potential involvement in AD phenotypes. We found that most clinical S. xylosus strains produce two PSMs, one of the shorter α- and one of the longer β-type, which were responsible for almost the entire lytic and pro-inflammatory capacities of S. xylosus. Importantly, PSMα of S. xylosus caused lysis and degranulation of mast cells at degrees higher than that of S. aureus δ-toxin, the main PSM previously associated with AD. However, S. xylosus did not produce significant AD symptoms in wild-type mice as opposed to S. aureus, indicating that promotion of AD by S. xylosus likely requires a predisposed host. Our study indicates that non-specific cytolytic potency rather than specific interaction underlies PSM-mediated mast cell degranulation and suggest that the previously reported exceptional potency of δ-toxin of S. aureus is due to its high-level production. Furthermore, they suggest that species that produce cytolytic PSMs, such as S. xylosus, all have the capacity to promote AD, but a high combined level of PSM cytolytic potency is required to cause AD in a non-predisposed host.

Potential of propolis antifungal activity for clinical applications

The high incidence of skin diseases of microbial origin along with the widespread increase of microbial resistance demand for therapeutic alternatives. Research on natural compounds has been opening new perspectives for the development of new therapies with health positive impacts. Propolis, a resinous mixture produced by honeybees from plant exudates, is widely used as a natural medicine since ancient times, mainly due to its antimicrobial properties. More recently, antioxidant, anti-tumor, anti-inflammatory, hepatoprotective and immunomodulatory activities were also reported for this natural product, highlighting its high potential pharmacological interest. In the present work, an extensive review of the main fungi causing skin diseases as well as the effects of natural compounds, particularly propolis, against such disease-causing microorganisms was organized and compiled in concise handy tables. This information allows to conclude that propolis is a highly effective antimicrobial agent suggesting that it could be used as an alternative skin treatment against pathogenic microorganisms and also as a cosmeceutic component or as a source of bioactive ingredients.

An Up-To-Date Review Regarding Cutaneous Benefits of Origanum vulgare L. Essential Oil

Due to the plethora of pharmacological activities reported in the literature, Origanum vulgare L. is a valuable aromatic plant for the medicine of the XXI century. Recent studies highlight that Origanum vulgare L. essential oil (OvEo) has gained attention in the dermatological field due to the cosmeceutical potential correlated with the presence of thymol and carvacrol. As a result of the fulminant expansion of bacterial resistance to antibiotics and the aggressiveness of skin infections, OvEo was extensively studied for its antimicrobial activity against Staphyloccocus spp. and Pseudomonas aeruginosa. Moreover, researchers have also assessed the anti-inflammatory activity of OvEo, suggesting its tissue remodeling and wound healing potential. Whereas OvEo comprises important biological activities that are used in a wide range of pathologies, recently, essential oils have shown great potential in the development of new therapeutic alternatives for skin disorders, such as acne, wounds or aging. Furthermore, substantial efforts have been committed to the development of modern formulations, such as microemulsions and nanoemulsions, in order to create the possibility for topical application. The review brings to the fore the most recent findings in the dermatological field regarding potential plant-based therapies involving OvEo, emphasizing the modern pharmaceutical formulation approaches and the cutaneous benefits in skin disorders.

Global Risk of Bacterial Skin Infections and Herpesviridae Infections with Ustekinumab, Secukinumab, and Tumour Necrosis Factor-alpha Inhibitors: Spontaneous Reports of Adverse Drug Reactions from the World Health Organization Pharmacovigilance Center

Genetic defects in interleukin-12/23/17 immunity are associated with an increased risk of Staphylococcus aureus and herpesvirus skin infections. This study analysed spontaneous safety reports from the WHO Pharmacovigilance Center of bacterial skin or herpesvirus infections associated with secukinumab, ustekinumab and tumour necrosis factor-α inhibitors. Associations found in disproportionality analyses were expressed as reporting odds ratios (ROR). For bacterial skin infections, ustekinumab showed the strongest association (ROR 6.09; 95% confidence interval (95% CI) 5.44-6.81), and, among the tumour necrosis factor-α inhibitors, infliximab showed the strongest association (ROR 4.18; 95% CI 3.97-4.40). Risk was comparable between infliximab and secukinumab (ROR 3.51; 95% CI 3.00-4.09). Secukinumab showed the strongest association with herpes simplex infection (ROR 4.80; 95% CI 3.78-6.10). All biologics were equally associated with herpes zoster. Infliximab was the only biologic associated with cytomegalovirus infection (ROR 5.66; 95% CI 5.08-6.31) and had the strongest association with Epstein-Barr virus infection (ROR 6.90; 95% CI 6.03-7.90). All biologics evaluated were positively associated with bacterial skin infections, herpes simplex, and herpes zoster, compared with all other drugs in the WHO database for which individual case safety reports were collected. The possibility of under-reporting, reporting bias and difference in causality assessment between countries and reporters must be taken into account when interpreting the results of disproportionality analyses.

Synergistic Antimicrobial Effect of Lactiplantibacillus plantarum and Lawsonia inermis Against Staphylococcus aureus

Purpose

The developed resistance of pathogenic microorganisms towards the currently used antimicrobial agents requires the fast search for newer potent antimicrobials. One of the most important ways to combat the previously mentioned disaster is the use of natural alternatives like medicinal plants. Our study aimed to estimate the anti-inflammatory property, and antibacterial effects of probiotics Lactiplantibacillus plantarum and ethanol extracts of Lawsonia inermis leaves against Staphylococcus aureus when they were used separately or collectively as synergism.

Material and Methods

Experimentally induced infected wound model in mice was created and divided into 10 groups then treated for two days by L. plantarum and L. inermis individually or in combination, followed by biochemical assays. The antibacterial, anti-inflammatory, and wound healing activity were evaluated through histopathological sections taken before and after treatment.

Results

Our results revealed that L. plantarum and L. inermis mixture could inhibit growth of S. aureus and decrease the minimal inhibitory concentration (MIC) of L. plantarum to 2 mg/mL. The mixture decreased level of both interleukin 6 (IL-6) and interferon-alpha (TNF-α) to a level near the normal uninfected group. Histopathological study showed that animals treated with both L. plantarum and L. inermis had achieved almost 90% healing.

Conclusion

These results suggest that L. plantarum and L. inermis mixture has synergistic effect on healing of infected wound.

Rapid pathogen-specific recruitment of immune effector cells in the skin by secreted toxins

Swift recruitment of phagocytic leucocytes is critical in preventing infection when bacteria breach through the protective layers of the skin. According to canonical models, this occurs via an indirect process that is initiated by contact of bacteria with resident skin cells and which is independent of the pathogenic potential of the invader. Here we describe a more rapid mechanism of leucocyte recruitment to the site of intrusion of the important skin pathogen Staphylococcus aureus that is based on direct recognition of specific bacterial toxins, the phenol-soluble modulins (PSMs), by circulating leucocytes. We used a combination of intravital imaging, ear infection and skin abscess models, and in vitro gene expression studies to demonstrate that this early recruitment was dependent on the transcription factor EGR1 and contributed to the prevention of infection. Our findings refine the classical notion of the non-specific and resident cell-dependent character of the innate immune response to bacterial infection by demonstrating a pathogen-specific high-alert mechanism involving direct recruitment of immune effector cells by secreted bacterial products.

Dihydrophenanthrenes from a Sicilian Accession of Himantoglossum robertianum (Loisel.) P. Delforge Showed Antioxidant, Antimicrobial, and Antiproliferative Activities

The peculiar aspect that emerges from the study of Orchidaceae is the presence of various molecules, which are particularly interesting for pharmaceutical chemistry due to their wide range of biological resources. The aim of our study was to investigate the properties of two dihydrophenanthrenes, isolated, for the first time, from Himantoglossum robertianum (Loisel.) P. Delforge (Orchidaceae) bulbs and roots. Chemical and spectroscopic study of the bulbs and roots of Himantoglossumrobertianum (Loisel.) P. Delforge resulted in the isolation of two known dihydrophenanthrenes-loroglossol and hircinol-never isolated from this plant species. The structures were evaluated based on ¹H-NMR, ¹³C-NMR, and two-dimensional spectra, and by comparison with the literature. These two molecules have been tested for their possible antioxidant, antimicrobial, antiproliferative, and proapoptotic activities. In particular, it has been shown that these molecules cause an increase in the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) in polymorphonuclear leukocytes (PMN); show antimicrobial activity against Escherichia coli and Staphylococcus aureus, and have anti-proliferative effects on gastric cancer cell lines, inducing apoptosis effects. Therefore, these two molecules could be considered promising candidates for pharmaceutical and nutraceutical preparations.

Wounds and Skin and Soft Tissue Infections in People Who Inject Drugs and the Utility of Syringe Service Programs in Their Management

Significance: Opioid use disorder and transition to injection drug use (IDU) are an urgent, nationwide public health crisis. Wounds and skin and soft tissue infections (SSTIs) are common complications of IDU that disproportionately affect people who inject drugs (PWID) and are a major source of morbidity and mortality for this population. Critical Issues: Injections in a nonsterile environment and reusing or sharing needles facilitates bacterial inoculation, with subsequent risk of serious complications such as sepsis, gangrene, amputation, and death. PWID are susceptible to infections with a wide spectrum of organisms beyond common culprits of SSTI, including Clostridium and Bacillus spp., as well as Candida. Recent Advances: Syringe services programs (SSPs) are cost-effective and successful in reducing harms associated with IDU. SSPs provide new equipment to PWID and aid in discarding used equipment. SSPs aim to reduce the risks of unhygienic injecting practices, which are associated with transmission of infections and blood-borne pathogens. Future Directions: Concurrently run SSPs and wound care clinics are uniquely positioned to facilitate care to PWID. Providing new, sterile equipment as well as early wound care intervention can reduce morbidity and mortality as well as health care expenditures by reducing the number of SSTI and injection-related wounds that require hospital admission. Establishment of wound care clinics as part of an SSP represents an untapped potential to reduce harm.

Trained Immunity as a Preventive Measure for Surgical Site Infections

Even with strict implementation of preventive measures, surgical site infections (SSIs) remain among the most prevalent health care-associated infections. New strategies to prevent SSIs would thus have a huge impact, also in light of increasing global rates of antimicrobial drug resistance. Considering the indispensable role of innate immune cells in host defense in surgical wounds, enhancing their function may represent a potential strategy for prevention of SSIs. Trained immunity is characterized by metabolic, epigenetic, and functional reprogramming of innate immune cells. These functional changes take place at multiple levels, namely, at the level of bone marrow precursors, circulating innate immune cells, and resident tissue macrophages. Experimental studies have shown that induction of trained immunity can protect against various infections. Increasing evidence suggests that it may also lower the risk and severity of SSIs. This may occur through several different mechanisms. First, trained immunity enhances local host defense against soft tissue infections, including those caused by Staphylococcus aureus, the most common cause of SSIs. Second, training effects on nonimmune cells such as fibroblasts have been shown to improve wound repair. Third, trained immunity may prevent or reverse the postoperative immunoparalysis that contributes to risk of infections following surgery. There are multiple approaches to inducing trained immunity, such as vaccination with the bacillus Calmette-Guérin (BCG) tuberculosis vaccine, topical administration of β-glucan, or treatment with the Toll-like receptor 7 agonist imiquimod. Clinical-experimental studies should establish if and how induction of trained immunity can best help prevent SSIs and what patient groups would most benefit.

Differential Early in vivo Dynamics and Functionality of Recruited Polymorphonuclear Neutrophils After Infection by Planktonic or Biofilm Staphylococcus aureus

Staphylococcus aureus is a human pathogen known for its capacity to shift between the planktonic and biofilm lifestyles. In vivo, the antimicrobial immune response is characterized by the recruitment of inflammatory phagocytes, namely polymorphonuclear neutrophils (PMNs) and monocytes/macrophages. Immune responses to planktonic bacteria have been extensively studied, but many questions remain about how biofilms can modulate inflammatory responses and cause recurrent infections in live vertebrates. Thus, the use of biologically sound experimental models is essential to study the specific immune signatures elicited by biofilms. Here, a mouse ear pinna model of infection was used to compare early innate immune responses toward S. aureus planktonic or biofilm bacteria. Flow cytometry and cytokine assays were carried out to study the inflammatory responses in infected tissues. These data were complemented with intravital confocal imaging analyses, allowing the real-time observation of the dynamic interactions between EGFP + phagocytes and bacteria in the ear pinna tissue of LysM-EGFP transgenic mice. Both bacterial forms induced an early and considerable recruitment of phagocytes in the ear tissue, associated with a predominantly pro-inflammatory cytokine profile. The inflammatory response was mostly composed of PMNs in the skin and the auricular lymph node. However, the kinetics of PMN recruitment were different between the 2 forms in the first 2 days post-infection (pi). Two hours pi, biofilm inocula recruited more PMNs than planktonic bacteria, but with decreased motility parameters and capacity to emit pseudopods. Inversely, biofilm inocula recruited less PMNs 2 days pi, but with an “over-activated” status, illustrated by an increased phagocytic activity, CD11b level of expression and ROS production. Thus, the mouse ear pinna model allowed us to reveal specific differences in the dynamics of recruitment and functional properties of phagocytes against biofilms. These differences would influence the specific adaptive immune responses to biofilms elicited in the lymphoid tissues.

Immunomodulatory and anti-infective effects of Cratylia mollis lectin (Cramoll) in a model of wound infection induced by Staphylococcus aureus

This work evaluated the immunomodulatory and anti-infective effects of Cratylia mollis lectin (Cramoll) in a model of wound infection induced by S. aureus. Swiss mice were divided into 3 groups (n = 12/group): non-inoculated (Control group); inoculated with S. aureus (Sa group); inoculated with S. aureus and treated with Cramoll (Sa + Cramoll group). In each animal, one lesion (64 mm²) was induced on the back and contaminated with S. aureus (~4.0 × 10⁶ CFU/wound). The treatment with Cramoll (5 μg/animal/day) started 1-day post-infection (dpi) and extended for 10 days. Clinical parameters (wound size, inflammatory aspects, etc.) were daily recorded; while cytokines levels, bacterial load and histological aspects were determined in the cutaneous tissue at 4^th dpi or 11^th dpi. The mice infected with S. aureus exhibited a delay in wound contraction and the highest inflammatory scores. These effects were impaired by the treatment with Cramoll which reduced the release of key inflammatory mediators (TNF-α, NO, VEGF) and the bacterial load at wound tissue. Histological evaluations showed a restauration of skin structures in the animals treated with Cramoll. Taken together, these results provide more insights about the healing and immunomodulatory properties of Cramoll and suggest this lectin as a lead compound for treatment of wound infection.

Effects of 17β-Estradiol on Monocyte/Macrophage Response to Staphylococcus aureus: An In Vitro Study

To describe how 17β-estradiol (E2) influence in the monocyte/macrophage response induced by S. aureus in in vitro models of murine peritoneal macrophages (MPMs) and human peripheral blood monocytes (HPBM). MPMs (2 x 10⁵/ml) were isolated from sham (n=3) and ovariectomized (OVX) females (n = 3) and males (n = 3) after induction by thioglycolate. The MPMs obtained from OVX females and males were treated for 24 hours with 17β-estradiol (E2) (10^-7 M), and after that, inoculation with S. aureus was carried out for 6 hours. The macrophages were collected and destined to evaluate the relative gene expression of TNF-α, IL-1β, IL-6, IL-8 and TLR2. For the in vitro model of HPBMs, six men and six women of childbearing age were selected and HPBMs were isolated from samples of the volunteers’ peripheral blood. In women, blood was collected both during menstruation and in the periovulatory period. HPBMs were inoculated with S. aureus for 6 hours and the supernatant was collected for analysis of cytokines by Luminex and the HPBMs were removed for analysis of 84 genes involved in the host’s response to bacterial infections by RT-PCR array. Previous treatment with E2 decreased the gene expression and production of proinflammatory cytokines, such as TNF-α, IL-1β and IL-6 and decreased the expression of TLR2 tanto em MPMs quanto em HPBMs. The analysis of gene expression shows that E2 inhibited the NFκB pathway. It is suggested that 17β-estradiol acts as an immunoprotective in the monocyte/macrophage response induced by S. aureus.

A comparative investigation on the role and interaction of EsxA and EsxB in host immune response

Staphylococcus aureus (S. aureus) is a frequent and major cause of bovine mastitis; it poses a tremendous economic burden to dairy industries of numerous countries. Early-secretion antigen-6 secretion system (ESS) has been viewed as an essential virulence and pathogenic factor of S. aureus. EsxA and EsxB are small acidic proteins secreted by ESS and identified as potential T-cell antigens of S. aureus. Unlike those of Mycobacterium tuberculosis (M. tuberculosis), the EsxA and EsxB of S. aureus do not form a dimer. Instead, EsxA dimerizes with itself or EsaC. Therefore, the interaction of EsxA and EsxB remains incompletely understood. In this study, to explore their interactions, EsxA and EsxB were expressed and used for immunization, alone or in combination, of murine infection models. Both components can interact with each other. Through the analysis of the immune response by immunological method, EsxB could significantly enhance the EsxA-specific IgG2a antibody level and increase the proliferation proportion of CD8⁺ T cells. These results indicate that when vaccinated with EsxA, EsxB can play a critical role in stimulating T helper 1 immunity by activating IgG2a and CD8⁺ T cells. We further show that vaccination with the combination of EsxA and EsxB resulted in enhanced stimulation of TLR-4 and improved protection against S. aureus. The findings may help us better understand the role of EsxB in the virulence and pathogenesis of S. aureus.

Murine Models for Staphylococcal Infection

Staphylococcus aureus is a Gram-positive bacterium that colonizes almost every organ in humans and mice and is a leading cause of diseases worldwide. S. aureus infections can be challenging to treat due to widespread antibiotic resistance and their ability to cause tissue damage. The primary modes of transmission of S. aureus are via direct contact with a colonized or infected individual or invasive spread from a colonization niche in the same individual. S. aureus can cause a myriad of diseases, including skin and soft tissue infections (SSTIs), osteomyelitis, pneumonia, endocarditis, and sepsis. S. aureus infection is characterized by the formation of purulent lesions known as abscesses, which are rich in live and dead neutrophils, macrophages, and surrounded by a capsule containing fibrin and collagen. Different strains of S. aureus produce varying amounts of toxins that evade and/or elicit immune responses. Therefore, animal models of S. aureus infection provide a unique opportunity to understand the dynamics of organ-specific immune responses and modifications in the pathogen that could favor the establishment of the pathogen. With advances in in vivo imaging of fluorescent transgenic mice, combined with fluorescent/bioluminescent bacteria, we can use mouse models to better understand the immune response to these types of infections. By understanding the host and bacterial dynamics within various organ systems, we can develop therapeutics to eliminate these pathogens. This module describes in vivo mouse models of both local and systemic S. aureus infection. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Murine model of Staphylococcus aureus subcutaneous infection Alternate Protocol: Murine tape stripping skin infection model Basic Protocol 2: Sample collection to determine skin structure, production of inflammatory mediators, and bacterial load Basic Protocol 3: Murine model of post-traumatic Staphylococcus aureus osteomyelitis Basic Protocol 4: Intravenous infection of the retro-orbital sinus Support Protocol: Preparation of the bacterial inoculum.

SOCS-1 inhibition of type I interferon restrains Staphylococcus aureus skin host defense

The skin innate immune response to methicillin-resistant Staphylococcus aureus (MRSA) culminates in the formation of an abscess to prevent bacterial spread and tissue damage. Pathogen recognition receptors (PRRs) dictate the balance between microbial control and injury. Therefore, intracellular brakes are of fundamental importance to tune the appropriate host defense while inducing resolution. The intracellular inhibitor suppressor of cytokine signaling 1 (SOCS-1), a known JAK/STAT inhibitor, prevents the expression and actions of PRR adaptors and downstream effectors. Whether SOCS-1 is a molecular component of skin host defense remains to be determined. We hypothesized that SOCS-1 decreases type I interferon production and IFNAR-mediated antimicrobial effector functions, limiting the inflammatory response during skin infection. Our data show that MRSA skin infection enhances SOCS-1 expression, and both SOCS-1 inhibitor peptide-treated and myeloid-specific SOCS-1 deficient mice display decreased lesion size, bacterial loads, and increased abscess thickness when compared to wild-type mice treated with the scrambled peptide control. SOCS-1 deletion/inhibition increases phagocytosis and bacterial killing, dependent on nitric oxide release. SOCS-1 inhibition also increases the levels of type I and type II interferon levels in vivo. IFNAR deletion and antibody blockage abolished the beneficial effects of SOCS-1 inhibition in vivo. Notably, we unveiled that hyperglycemia triggers aberrant SOCS-1 expression that correlates with decreased overall IFN signatures in the infected skin. SOCS-1 inhibition restores skin host defense in the highly susceptible hyperglycemic mice. Overall, these data demonstrate a role for SOCS-1-mediated type I interferon actions in host defense and inflammation during MRSA skin infection.

Protein A Modulates Neutrophil and Keratinocyte Signaling and Survival in Response to Staphylococcus aureus

The type 1 TNF-α receptor (TNFR1) has a central role in initiating both pro-inflammatory and pro-apoptotic signaling cascades in neutrophils. Considering that TNFR1 signals Staphylococcus aureus protein A (SpA), the aim of this study was to explore the interaction of this bacterial surface protein with neutrophils and keratinocytes to underscore the signaling pathways that may determine the fate of these innate immune cells in the infected tissue during staphylococcal skin infections. Using human neutrophils cultured in vitro and isogenic staphylococcal strains expressing or not protein A, we demonstrated that SpA is a potent inducer of IL-8 in neutrophils and that the induction of this chemokine is dependent on the SpA-TNFR1 interaction and p38 activation. In addition to IL-8, protein A induced the expression of TNF-α and MIP-1α highlighting the importance of SpA in the amplification of the inflammatory response. Protein A contributed to reduce neutrophil mortality prolonging their lifespan upon the encounter with S. aureus. Signaling initiated by SpA modulated the type of neutrophil cell death in vitro and during skin and soft tissue infections (SSTI) in vivo triggering the apoptotic pathway instead of necrosis. Moreover, SpA induced pro-inflammatory cytokines in keratinocytes, modulating their survival in vitro and preventing the exacerbated necrosis and ulceration of the epithelium during SSTI in vivo. Taken together, these results highlight the importance of the inflammatory signaling induced by protein A in neutrophils and skin epithelial cells. The ability of protein A to modulate the neutrophil/epithelial cell death program in the skin is of clinical relevance considering that lysis of neutrophils and epithelial cells will promote an intense inflammatory response and contribute to tissue damage, a non-desirable feature of complicated SSTI.

Distinctive Under-Expression Profile of Inflammatory and Redox Genes in the Blood of Elderly Patients with Cardiovascular Disease

Purpose

Chronic low-grade inflammation and oxidative stress are present in most of the pathologic mechanisms underlying non-communicable diseases. Inflammation and redox biomarkers might therefore have a value in disease prognosis and therapy response. In this context, we performed a case–control study for assessing in whole blood the expression profile of inflammation and redox-related genes in elderly subjects with various comorbidities.

Patients and Methods

In the blood of 130 elderly subjects with various pathologies (cardiovascular disease, hypertension, dyslipidemia including hypercholesterolemia, type 2 diabetes mellitus), kept under control by polyvalent disease-specific medication, we investigated by pathway-focused qRT-PCR a panel comprising 84 inflammation-related and 84 redox-related genes.

Results

The study highlights a distinctive expression profile of genes critically involved in NF-κB-mediated inflammation and redox signaling in the blood of patients with cardiovascular disease, characterized by significant down-regulation of the genes NFKB2, NFKBIA, RELA, RELB, AKT1, IRF1, STAT1, CD40, LTA, TRAF2, PTGS1, ALOX12, DUOX1, DUOX2, MPO, GSR, TXNRD2, HSPA1A, MSRA, and PDLIM1. This gene expression profile defines the transcriptional status of blood leukocytes in stable disease under medication control, without discriminating between disease- and therapy-related changes.

Conclusion

The study brings preliminary proof on a minimally invasive strategy for monitoring disease in patients with cardiovascular pathology, from the point of view of inflammation or redox dysregulation in whole blood.

In Vivo and In Vitro Assessments of the Antibacterial Potential of Chitosan-Silver Nanocomposite Against Methicillin-Resistant Staphylococcus aureus-Induced Infection in Rats

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most threatening multidrug-resistant bacteria worldwide. Owing to their efficient antimicrobial properties, nanoparticles have been widely used as an alternative approach for combating the antibiotic-resistant bacteria. Consequently, this study was designed to compare in between the bactericidal effect of low doses (5 mg/kg bwt) of nanoparticles of chitosan (Ch-NPs), silver (Ag-NPs), and chitosan-silver nanocomposites (Ch-Ag NCs) both in vitro and in vivo against experimentally chronic infection induced by methicillin-resistant Staphylococcus aureus (MRSA). The three forms of nanoparticles were tested for their in vitro antimicrobial potential against MRSA by detection of MICs and MBCs using microdilution method. In vivo, thirty-five male albino Wistar rats were used and divided into five groups (n = 7). Group l (negative control), group 2 (MRSA infected and untreated), groups 3, 4, and 5 (MRSA infected then treated with Ch-NPs, Ag-NPs, and Ch-Ag NCs respectively for 7 days). After 6 weeks, blood samples were collected then rats were euthanized to collect different organs (liver, spleen, lungs, and kidneys). Some of them were kept in 10% formalin for histopathological investigations while others used for bacterial re-isolation. Ch-Ag NCs showed the lowest MIC and MBC among the tested nanoparticles. Moreover, the highest histopathological scoring was observed in the infected and untreated group while the lowest scoring was detected in groups treated with Ch-Ag NCs in comparison with the negative control group. The highest bacterial count was noticed in the infected and untreated group followed by those treated with Ch-NPs while the lowest count was observed in group treated with Ch-Ag NCs. Depending on these results, it can be concluded that Ch-Ag NCs have a strong bactericidal effect against MRSA and may be used as alternative option to antibiotics.

Peptides from Animal Origin: A Systematic Review on Biological Sources and Effects on Skin Wounds

Background

Skin wounds are closely correlated with opportunistic infections and sepsis risk. Due to the need of more efficient healing drugs, animal peptides are emerging as new molecular platforms to accelerate skin wound closure and to prevent and control bacterial infection.

Aim

The aim of this study was to evaluate the preclinical evidence on the impact of animal peptides on skin wound healing. In addition, we carried out a critical analysis of the studies' methodological quality. Main Methods. This systematic review was performed according to the PRISMA guidelines, using a structured search on the PubMed-Medline, Scopus, and Web of Science platforms to retrieve studies published until August 25, 2020 at 3 : 00 pm. The studies included were limited to those that used animal models, investigated the effect of animal peptides with no association with other compounds on wound healing, and that were published in English. Bias analysis and methodological quality assessments were examined through the SYRCLE's RoB tool.

Results

Thirty studies were identified using the PRISMA workflow. In general, animal peptides were effective in accelerating skin wound healing, especially by increasing cellular proliferation, neoangiogenesis, colagenogenesis, and reepithelialization. Considering standardized methodological quality indicators, we identified a marked heterogeneity in research protocols and a high risk of bias associated with limited characterization of the experimental designs.

Conclusion

Animal peptides show a remarkable healing potential with biotechnological relevance for regenerative medicine. However, rigorous experimental approaches are still required to clearly delimit the mechanisms underlying the healing effects and the risk-benefit ratio attributed to peptide-based treatments.

(+)-(E)-Chrysanthenyl Acetate: A Molecule with Interesting Biological Properties Contained in the Anthemis secundiramea (Asteraceae) Flowers

Anthemis secundiramea is a perennial herb native widespread throughout the Mediterranean basin. The oil obtained from the flowers of this plant has antimicrobial properties against gram-positive and -negative bacteria, and inhibits the biofilm formation. The extract of A. secundiramea also has antioxidant activity—increasing the activity of different enzymes (SOD, CAT, and GPx). Surprisingly, in the oil extracted from the flowers, there is a single molecule, called (+)-(E)-chrysanthenyl acetate: This makes the A. secundiramea flowers extract extremely interesting for future topical, cosmetic, and nutraceutical applications.

Harnessing antifungal immunity in pursuit of a Staphylococcus aureus vaccine strategy

Staphylococcus aureus (S. aureus) is one of the most common bacterial infections worldwide, and antibiotic resistant strains such as Methicillin-Resistant S. aureus (MRSA) are a major threat and burden to public health. MRSA not only infects immunocompromised patients but also healthy individuals and has rapidly spread from the healthcare setting to the outside community. However, all vaccines tested in clinical trials to date have failed. Immunocompromised individuals such as patients with HIV or decreased levels of CD4+ T cells are highly susceptible to S. aureus infections, and they are also at increased risk of developing fungal infections. We therefore wondered whether stimulation of antifungal immunity might promote the type of immune responses needed for effective host defense against S. aureus. Here we show that vaccination of mice with a fungal β-glucan particle (GP) loaded with S. aureus antigens provides protective immunity to S. aureus. We generated glucan particles loaded with the four S. aureus proteins ClfA, IsdA, MntC, and SdrE, creating the 4X-SA-GP vaccine. Vaccination of mice with three doses of 4X-SA-GP promoted protection in a systemic model of S. aureus infection with a significant reduction in the bacterial burden in the spleen and kidneys. 4X-SA-GP vaccination induced antigen-specific Th1 and Th17 CD4+ T cell and antibody responses and provided long-term protection. This work suggests that the GP vaccine system has potential as a novel approach to developing vaccines for S. aureus.

Bacterial extracellular vesicle-coated multi-antigenic nanovaccines protect against drug-resistant Staphylococcus aureus infection by modulating antigen processing and presentation pathways

Background: Vaccination provides an alternative to antibiotics in addressing drug-resistant Staphylococcus aureus (S. aureus) infection. However, vaccine potency is often limited by a lack of antigenic breadth and a demand on the generation of antibody responses alone.

Methods: In this study, bacterial extracellular vesicles (EVs) coating indocyanine green (ICG)-loaded magnetic mesoporous silica nanoparticles (MSN) were constructed as multi-antigenic vaccines (EV/ICG/MSN) with the ability to modulate antigen presentation pathways in dendritic cells (DCs) to induce cellular immune responses.

Results: Exposing the EV/ICG/MSNs to a laser could promote DC maturation and enhance the proteasome-dependent antigen presentation pathway by facilitating endolysosomal escape, improving proteasome activity, and elevating MHC-I expression. Immunization by EV/ICG/MSNs with laser irradiation in vivo triggered improved CD8⁺ T cell responses while maintaining CD4⁺ T cell responses and humoral immunity. In addition, in vivo tracking data revealed that the vaccine could be efficiently transported from the injection site into lymph nodes. Skin infection experiments showed that the vaccine not only prevented and treated superficial infection but also decreased bacterial invasiveness, thus strongly suggesting that EV/ICG/MSNs were effective in preventing complications resulting from the introduction of S. aureus infections.

Conclusion: This multi-antigenic nanovaccine-based modulation of antigen presentation pathways provides an effective strategy against drug-resistant S. aureus infection.

Human Defensins: A Novel Approach in the Fight against Skin Colonizing Staphylococcus aureus

Staphylococcus aureus is a microorganism capable of causing numerous diseases of the human skin. The incidence of S. aureus skin infections reflects the conflict between the host skin′s immune defenses and the S. aureus’ virulence elements. Antimicrobial peptides (AMPs) are small protein molecules involved in numerous biological activities, playing a very important role in the innate immunity. They constitute the defense of the host′s skin, which prevents harmful microorganisms from entering the epithelial barrier, including S. aureus. However, S. aureus uses ambiguous mechanisms against host defenses by promoting colonization and skin infections. Our review aims to provide a reference collection on host-pathogen interactions in skin disorders, including S. aureus infections and its resistance to methicillin (MRSA). In addition to these, we discuss the involvement of defensins and other innate immunity mediators (i.e., toll receptors, interleukin-1, and interleukin-17), involved in the defense of the host against the skin disorders caused by S. aureus, and then focus on the evasion mechanisms developed by the pathogenic microorganism under analysis. This review provides the “state of the art” on molecular mechanisms underlying S. aureus skin infection and the pharmacological potential of AMPs as a new therapeutic strategy, in order to define alternative directions in the fight against cutaneous disease.

Pathogenesis of Intradermal Staphylococcal Infections: Rabbit Experimental Approach to Natural Staphylococcus aureus Skin Infections

Despite the enormous efforts made to achieve effective tools that fight against Staphylococcus aureus, the results have not been successful. This failure may be due to the absence of truly representative experimental models. To overcome this deficiency, the present work describes and immunologically characterizes the infection for 28 days, in an experimental low-dose (300 colony-forming units) intradermal model of infection in rabbits, which reproduces the characteristic staphylococcal abscess. Surprisingly, when mutant strains in the genes involved in virulence (JΔagr, JΔcoaΔvwb, JΔhla, and JΔpsmα) were inoculated, no strong effect on the severity of lesions was observed, unlike other models that use high doses of bacteria. The inoculation of a human rabbitized (FdltB^r) strain demonstrated its capacity to generate a similar inflammatory response to a wild-type rabbit strain and, therefore, validated this model for conducting these experimental studies with human strains. To conclude, this model proved reproducible and may be an option of choice to check both wild-type and mutant strains of different origins.

Novel Resolution Mediators of Severe Systemic Inflammation

Nonresolving inflammation, a hallmark of underlying severe inflammatory processes such as sepsis, acute respiratory distress syndrome and multiple organ failure is a major cause of admission to the intensive care unit and high mortality rates. Many survivors develop new functional limitations and health problems, and in cases of sepsis, approximately 40% of patients are rehospitalized within three months. Over the last few decades, better treatment approaches have been adopted. Nevertheless, the lack of knowledge underlying the complex pathophysiology of the inflammatory response organized by numerous mediators and the induction of complex networks impede curative therapy. Thus, increasing evidence indicates that resolution of an acute inflammatory response, considered an active process, is the ideal outcome that leads to tissue restoration and organ function. Many mediators have been identified as immunoresolvents, but only a few have been shown to contribute to both the initial and resolution phases of severe systemic inflammation, and these agents might finally substantially impact the therapeutic approach to severe inflammatory processes. In this review, we depict different resolution mediators/immunoresolvents contributing to resolution programmes specifically related to life-threatening severe inflammatory processes.

Exploring the complex role of chemokines and chemoattractants in vivo on leukocyte dynamics

Chemotaxis is fundamental for leukocyte migration in immunity and inflammation and contributes to the pathogenesis of many human diseases. Although chemokines and various other chemoattractants were initially appreciated as important mediators of acute inflammation, in the past years they have emerged as critical mediators of cell migration during immune surveillance, organ development, and cancer progression. Such advances in our knowledge in chemokine biology have paved the way for the development of specific pharmacological targets with great therapeutic potential. Chemoattractants may belong to different classes, including a complex chemokine system of approximately 50 endogenous molecules that bind to G protein-coupled receptors, which are expressed by a wide variety of cell types. Also, an unknown number of other chemoattractants may be generated by pathogens and damaged/dead cells. Therefore, blocking chemotaxis without causing side effects is an extremely challenging task. In this review, we focus on recent advances in understanding how the chemokine system orchestrates immune cell migration and positioning at the whole organ level in homeostasis, inflammation, and infection.

Identification of Key Determinants of Staphylococcus aureus Vaginal Colonization

Staphylococcus aureus is an important pathogen responsible for nosocomial and community-acquired infections in humans, and methicillin-resistant S. aureus (MRSA) infections have continued to increase despite widespread preventative measures. S. aureus can colonize the female vaginal tract, and reports have suggested an increase in MRSA infections in pregnant and postpartum women as well as outbreaks in newborn nurseries. Currently, little is known about specific factors that promote MRSA vaginal colonization and subsequent infection. To study S. aureus colonization of the female reproductive tract in a mammalian system, we developed a mouse model of S. aureus vaginal carriage and demonstrated that both hospital-associated and community-associated MRSA isolates can colonize the murine vaginal tract. Immunohistochemical analysis revealed an increase in neutrophils in the vaginal lumen during MRSA colonization. Additionally, we observed that a mutant lacking fibrinogen binding adhesins exhibited decreased persistence within the mouse vagina. To further identify novel factors that promote vaginal colonization, we performed RNA sequencing to determine the transcriptome of MRSA growing in vivo during vaginal carriage at 5 h, 1 day, and 3 days postinoculation. Over 25% of the bacterial genes were differentially regulated at all time points during colonization compared to laboratory cultures. The most highly induced genes were those involved in iron acquisition, including the Isd system and siderophore transport systems. Mutants deficient in these pathways did not persist as well during in vivo colonization. These results reveal that fibrinogen binding and the capacity to overcome host nutritional limitation are important determinants of MRSA vaginal colonization.IMPORTANCE Staphylococcus aureus is an opportunistic pathogen able to cause a wide variety of infections in humans. Recent reports have suggested an increasing prevalence of MRSA in pregnant and postpartum women, coinciding with the increased incidence of MRSA infections in neonatal intensive care units (NICUs) and newborn nurseries. Vertical transmission from mothers to infants at delivery is a likely route of MRSA acquisition by the newborn; however, essentially nothing is known about host and bacterial factors that influence MRSA carriage in the vagina. Here, we established a mouse model of vaginal colonization and observed that multiple MRSA strains can persist in the vaginal tract. Additionally, we determined that MRSA interactions with fibrinogen and iron uptake can promote vaginal persistence. This study is the first to identify molecular mechanisms which govern vaginal colonization by MRSA, the critical initial step preceding infection and neonatal transmission.