Induction of cell-mediated immunity to Staphylococcus aureus in the mouse mammary gland by local immunization with a live attenuated mutant

Vitexin Mitigates Staphylococcus aureus-Induced Mastitis via Regulation of ROS/ER Stress/NF-κB/MAPK Pathway

Mastitis, caused by a variety of pathogenic microorganisms, seriously threatens the safety and economic benefits of the dairy industry. Vitexin, a flavone glucoside found in many plant species, has been widely reported to have antioxidant, anti-inflammatory, antiviral, anticancer, neuroprotective, and cardioprotective effects. However, few studies have explored the effect of vitexin on mastitis. This study is aimed at exploring whether the antioxidant and anti-inflammatory functions of vitexin can improve Staphylococcus aureus-induced mastitis and its possible molecular mechanism. The expression profiles of S. aureus-infected bovine mammary epithelial cells and gland tissues from the GEO data set (GSE94056 and GSE139612) were analyzed and found that DEGs were mainly involved in immune signaling pathways, apoptosis, and ER stress through GO and KEGG enrichment. Vitexin blocked the production of ROS and increased the activity of antioxidant enzymes (SOD, GSH-PX, and CAT) via activation of PPARγ in vivo and in vitro. In addition, vitexin reduced the production of inflammatory cytokines (TNF-α, IL-1β, and IL-6) and inhibited apoptosis in MAC-T cells and mouse mammary tissues infected with Staphylococcus aureus. Moreover, vitexin decreased the expression of PDI, Ero1-Lα, p-IRE1α, PERK, p-eIF2α, and CHOP protein but increased BiP in both mammary gland cells and tissues challenged by S. aureus. Western blot results also found that the phosphorylation levels of JNK, ERK, p38, and p65 were reduced in vitexin-treated tissues and cells. Vitexin inhibited the production of ROS through promoting PPARγ, increased the activity of antioxidant enzymes, and reduced inflammatory cytokines and apoptosis by alleviating ER stress and inactivation MAPKs and NF-κB signaling pathway. Vitexin maybe have great potential to be a preventive and therapeutic agent for mastitis.

Evaluation of the Efficacy of a Cholera-Toxin-Based Staphylococcus aureus Vaccine against Bovine Intramammary Challenge

Staphylococcus aureus (S. aureus) is a primary agent of bovine mastitis and a source of significant economic loss for the dairy industry. We previously reported antigen-specific immune induction in the milk and serum of dairy cows following vaccination with a cholera toxin A₂ and B subunit (CTA₂/B) based vaccine containing the iron-regulated surface determinant A (IsdA) and clumping factor A (ClfA) antigens of S. aureus (IsdA + ClfA-CTA₂/B). The goal of the current study was to assess the efficacy of this vaccine to protect against S. aureus infection after intramammary challenge. Six mid-lactation heifers were randomized to vaccinated and control groups. On days 1 and 14 animals were inoculated intranasally with vaccine or vehicle control, and on day 20 animals were challenged with S. aureus. Clinical outcome, milk quality, bacterial shedding, and somatic cell count (SCC) were followed for ten days post-challenge. Vaccinated animals did not show signs of clinical S. aureus mastitis and had lower SCCs compared to control animals during the challenge period. Reductions in bacterial shedding were observed but were not significant between groups. Antibody analysis of milk and serum indicated that, upon challenge, vaccinated animals produced enhanced IsdA- and ClfA-CTA₂/B specific immunoglobulin G (IgG) responses, while responses to CTA₂/B alone were not different between groups. Responses after challenge were largely IgG1 against the IsdA antigen and mixed IgG1/IgG2 against the ClfA antigen. In addition, there was a significant increase in interferon gamma (IFN-γ) expression from blood cells in vaccinated animals on day 20. While preliminary, these findings support evidence of the induction of active immunity by IsdA + ClfA-CTA₂/B, and further assessment of this vaccine is warranted.

Efficacy of Aloe vera, Ananas comosus, and Sansevieria masoniana Cream on the Skin Wound Infected with MRSA

The tropical area has a lot of herbal medicines such as Aloe vera (AV), Ananas comosus (AC), and Sansevieria masoniana (SM). All the three have a unique potential effect as an antibacterial and wound-healing promoter. The aim of this study is to explore the role of AV, AC, and SM on the skin wound infected with methicillin-resistant Staphylococcus aureus (MRSA). Forty-five adult female Sprague Dawley rats weighing 250–300 grams were divided into 5 groups. All the groups were exposed to two round full-thickness punch biopsy and infected with MRSA. The group C was the control group/untreated; group BC was treated with base cream/without extract; group AV was treated with 75% AV cream; group AC was treated with 75% AC cream, and group SM was treated with 75% SM cream. The wounds were observed on days 5, 10, and 15. The healing of skin wounds was measured by a percentage of closure, skin tensile strength, and histopathology. The result showed that AV, AC, and SM have a similar potential effect on healing in the wound that was infected with MRSA compared to the groups C and BC (P < 0.05). It shows that all the three herbal formulations can be used as the alternative therapy to the wound infected with MRSA.

Generation of a Novel Staphylococcus aureus Ghost Vaccine and Examination of Its Immunogenicity against Virulent Challenge in Rats

Staphylococcus aureus is a Gram-positive pathogen that causes a wide range of infections in humans and animals. Bacterial ghosts are nonliving, empty cell envelopes and are well represented as novel vaccine candidates. In this study, we examined the immunogenicity and protective efficacy of S. aureus ghosts (SAGs) against a virulent challenge in rats. Nonliving SAGs were generated by using the MIC of sodium hydroxide. The formation of a transmembrane lysis tunnel structure in SAGs was visualized by scanning electron microscopy. To investigate these SAGs as a vaccine candidate, rats were divided into four groups, A (nonimmunized control), B (orally immunized), C (subcutaneously immunized), and D (intravenously immunized). The IgG antibody responses were significantly stronger in the SAG-immunized groups than in the nonimmunized control group (P < 0.05). Moreover, a significant increase in the populations of CD4(+) and CD8(+) T cells was observed in all three immunized groups (P < 0.05). We also found that serum bactericidal antibodies were significantly elicited in the SAG-immunized groups (P < 0.05). Most importantly, the bacterial loads in the immunized groups were significantly lower than those in the nonimmunized control group (P < 0.01). These results suggest that immunization with SAGs induces immune responses and provides protection against a virulent S. aureus challenge.

Comparative studies of the immunogenicity and protective potential of biofilm vs planktonic Staphylococcus aureus vaccine against bovine mastitis using non-invasive mouse mastitis as a model system

This study was undertaken to compare the immunogenicity and protective potential of biofilm vs planktonic Staphylococcus aureus vaccine for the prevention of mastitis using the mouse as a model system. Mice immunized with formalin-killed whole cell vaccine of S. aureus residing in a biofilm when delivered via an intramammary route produced a cell mediated immune response. Mice immunized with this biofilm vaccine showed significant reductions in colonization by S. aureus in mammary glands, severity of clinical symptoms and tissue damage in mammary glands in comparison with the mice immunized with formalin-killed whole cells of planktonic S. aureus. The planktonic vaccine administered by a subcutaneous route produced a significantly higher humoral immune response (IgG1 and IgG) than the biofilm vaccine. However, considering the host response, tissue damage, the clinical severity and colonization of S. aureus in mammary glands, the biofilm vaccine performed better in immunogenicity and protective potential when administered by the intramammary route.

CD4 T cell antigens from Staphylococcus aureus Newman strain identified following immunization with heat-killed bacteria

Staphylococcus aureus is a commensal bacterium associated with the skin and mucosal surfaces of humans and animals that can also cause chronic infection. The emergence of antibiotic-resistant strains such as methicillin-resistant S. aureus (MRSA) and strains causing chronic intramammary infections (IMI) in cows results in severe human and livestock infections. Conventional approaches to vaccine development have yielded only a few noneffective vaccines against MRSA or IMI strains, so there is a need for improved vaccine development. CD4 T lymphocytes are required for promoting gamma interferon (IFN-γ) mediated immunoglobulin isotype switching in B lymphocytes to produce high-affinity IgG antibodies and IFN-γ-mediated phagocyte activation for an effective resolution of bacterial infection. However, the lack of known CD4 T cell antigens from S. aureus has made it difficult to design effective vaccines. The goal of this study was to identify S. aureus proteins recognized by immune CD4 T cells. Using a reverse genetics approach, 43 antigens were selected from the S. aureus Newman strain. These included lipoproteins, proteases, transcription regulators, an alkaline shock protein, conserved-domain proteins, hemolysins, fibrinogen-binding protein, staphylokinase, exotoxin, enterotoxin, sortase, and protein A. Screening of expressed proteins for recall T cell responses in outbred, immune calves identified 13 proteins that share over 80% sequence identity among MRSA or IMI strains. These may be useful for inclusion in a broadly protective multiantigen vaccine against MRSA or IMI.

Targeting mucosal immunity in the battle to develop a mastitis vaccine

The mucosal immune system encounters antigens that enhance and suppress immune function, and serves as a selective barrier against invading pathogens. The mammary gland not only encounters antigens but also produces a nutrient evolved to protect and enhance mucosal development in the neonate. Efforts to manipulate antibody concentrations in milk to prevent mastitis, an infection of the mammary gland, have been hampered both by complexity and variation in target pathogens and limited knowledge of cellular immunity in the gland. Successful vaccination strategies must overcome the natural processes that regulate types and concentrations of milk antibodies for neonatal development, and enhance cellular immunity. Furthermore, the need to overcome dampening of immunity caused by non-pathogenic encounters to successfully prevent establishment of infection is an additional obstacle in vaccine development at mucosal sites. A significant mastitis pathogen, Staphylococcus aureus, not only resides as a normal flora on a multitude of species, but also causes clinical disease with limited treatment options. Using the bovine model of S. aureus mastitis, researchers can decipher the role of antigen selection and presentation by mammary dendritic cells, enhance development of central and effector memory function, and subsequently target specific memory cells to the mammary gland for successful vaccine development. This brief review provides an overview of adaptive immunity, previous vaccine efforts, current immunological findings relevant to enhancing immune memory, and research technologies that show promise in directing future vaccine efforts to enhance mammary gland immunity and prevent mastitis.

Suppression of the inflammatory immune response prevents the development of chronic biofilm infection due to methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is a common cause of prosthetic implant infections, which can become chronic due to the ability of S. aureus to grow as a biofilm. Little is known about adaptive immune responses to these infections in vivo. We hypothesized that S. aureus elicits inflammatory Th1/Th17 responses, associated with biofilm formation, instead of protective Th2/Treg responses. We used an adapted mouse model of biofilm-mediated prosthetic implant infection to determine chronic infection rates, Treg cell frequencies, and local cytokine levels in Th1-biased C57BL/6 and Th2-biased BALB/c mice. All C57BL/6 mice developed chronic S. aureus implant infection at all time points tested. However, over 75% of BALB/c mice spontaneously cleared the infection without adjunctive therapy and demonstrated higher levels of Th2 cytokines and anti-inflammatory Treg cells. When chronic infection rates in mice deficient in the Th2 cytokine interleukin-4 (IL-4) via STAT6 mutation in a BALB/c background were assessed, the mice were unable to clear the S. aureus implant infection. Additionally, BALB/c mice depleted of Treg cells via an anti-CD25 monoclonal antibody (MAb) were also unable to clear the infection. In contrast, the C57BL/6 mice that were susceptible to infection were able to eliminate S. aureus biofilm populations on infected intramedullary pins once the Th1 and Th17 responses were diminished by MAb treatment with anti-IL-12 p40. Together, these results indicate that Th2/Treg responses are mechanisms of protection against chronic S. aureus implant infection, as opposed to Th1/Th17 responses, which may play a role in the development of chronic infection.

Role of interleukin-17A in cell-mediated protection against Staphylococcus aureus infection in mice immunized with the fibrinogen-binding domain of clumping factor A

Clumping factor A (ClfA) is a fibrinogen-binding cell wall-attached protein and an important virulence factor of Staphylococcus aureus. Previous studies reported that an immunization with the fibrinogen-binding domain of ClfA (ClfA(40-559)) protected animals against S. aureus infection. It was reported that some cytokines are involved in the pathogenesis of staphylococcal diseases and in host defense against S. aureus infection. However, the role of cytokines in the protective effect of ClfA(40-559) as a vaccine has not been elucidated. In this study, we demonstrated that the spleen cells of ClfA(40-559)-immunized mice produced a large amount of interleukin-17A (IL-17A). The protective effect of immunization was exerted in wild-type mice but not in IL-17A-deficient mice. IL-17A mRNA expression was increased in the spleens and kidneys of immunized mice after infection. CXCL2 and CCL2 mRNA expression was increased in the spleens and kidneys, respectively. Consistent with upregulation of the mRNA expression, neutrophils infiltrated into the spleens extensively and macrophage infiltration was observed in the kidneys of immunized mice. These results suggest that immunization with ClfA(40-559) induces the IL-17A-producing cells and that IL-17-mediated cellular immunity is involved in the protective effect induced by immunization with ClfA(40-559) against S. aureus infection.

Phytol-based novel adjuvants in vaccine formulation: 2. Assessment of efficacy in the induction of protective immune responses to lethal bacterial infections in mice

BACKGROUND

Adjuvants are known to significantly enhance vaccine efficacy. However, commercial adjuvants often have limited use because of toxicity in humans. The objective of this study was to determine the comparative effectiveness of a diterpene alcohol, phytol and its hydrogenated derivative PHIS-01, relative to incomplete Freund's adjuvant (IFA), a commonly used adjuvant in augmenting protective immunity in mice against E. coli and S. aureus, and in terms of inflammatory cytokines.

METHODS

Vaccines, consisting of heat-attenuated E. coli or S. aureus and either of the two phytol-based adjuvants or IFA, were tested in female BALB/c mice. The vaccines were administered intraperitoneally at 10-day intervals. The efficacy of the phytol and PHIS-01, as compared to IFA, was assessed by ELISA in terms of anti-bacterial antibody and inflammatory cytokines. We also examined the ability of the vaccines to induce specific protective immunity by challenging mice with different doses of live bacteria.

RESULTS AND DISCUSSION

IFA, phytol, and PHIS-01 were equally efficient in evoking anti-E. coli antibody response and in providing protective immunity against live E. coli challenges. In contrast, the antibody response to S. aureus was significant when PHIS-01 was used as the adjuvant. However, in terms of the ability to induce protective immunity, phytol was most effective against S. aureus. Moreover, during challenges with live E. coli and S. aureus immune mice produced much less IL-6, the mediators of fatal septic shock syndromes.

CONCLUSION

Our results show that vaccine formulations containing phytol and PHIS-01 as adjuvants confer a robust and protective immunity against both Gram-negative and Gram-positive bacteria without inducing adverse inflammatory cytokine due to IL-6.

The role of gamma interferon in acquired host resistance against Staphylococcus aureus infection in mice

We investigated the expression of an acquired host resistance against Staphylococcus aureus infection in mice. When C57BL/6 mice were immunized with viable S. aureus and challenged with S. aureus eight weeks later, the elimination of S. aureus from the spleen and liver was enhanced in the immunized mice compared with the nonimmunized mice. When gamma interferon (IFN-gamma(-/-)) mice were immunized and challenged, the bacterial numbers in the organs of immunized mice were comparable to those in the nonimmunized mice, suggesting that IFN-gamma plays a critical role in an acquired host resistance against S. aureus infection. IFN-gamma(-/-) mice produced the lower level of anti-S. aureus immunoglobulin M (IgM) and IgG2a antibodies compared with C57BL/6 mice. To elucidate the role of IFN-gamma produced during a challenge with S. aureus, a single injection of anti-IFN-gamma monoclonal antibody to mice was carried out 1 h before challenge. An acquired resistance against S. aureus infection was inhibited by injecting with anti-IFN-gamma monoclonal antibody. However, anti-IFN-gamma monoclonal antibody treatment failed to modulate anti-S. aureus IgM, IgG1 or IgG2a responses in these animals. These results demonstrated that IFN-gamma is required for an acquired resistance against S. aureus infection in mice. However, IFN-gamma induced during the challenge failed to affect the secondary antibody responses.

Attenuation and persistence of and ability to induce protective immunity to a Staphylococcus aureus aroA mutant in mice

Staphylococcus aureus is the most important etiological agent of bovine mastitis, a disease that causes significant economic losses to the dairy industry. Several vaccines to prevent the disease have been tested, with limited success. The aim of this study was to obtain a suitable attenuated aro mutant of S. aureus by transposon mutagenesis and to demonstrate its efficacy as a live vaccine to induce protective immunity in a murine model of intramammary infection. To do this, we transformed S. aureus RN6390 with plasmid pTV1ts carrying Tn917. After screening of 3,493 erythromycin-resistant colonies, one mutant incapable of growing on plates lacking phenylalanine, tryptophan, and tyrosine was isolated and characterized. Molecular characterization of the mutant showed that the affected gene was aroA and that the insertion occurred 756 bp downstream of the aroA start codon. Complementation of the aroA mutant with a plasmid carrying aroA recovered the wild-type phenotype. The mutant exhibited a 50% lethal dose (1 x 10(6) CFU/mouse) higher than that of the parental strain (4.3 x 10(4) CFU/mouse). The aroA mutant showed decreased ability to persist in the lungs, spleens, and mammary glands of mice. Intramammary immunization with the aroA mutant stimulated both Th1 and Th2 responses in the mammary gland, as ascertained by reverse transcription-PCR, and induced significant protection from challenge with either the parental wild-type or a heterologous strain isolated from a cow with mastitis.

Mouse models to study the pathogenesis and control of bovine mastitis. A review

Mastitis is a major infectious disease affecting high yielding cows in dairy herds. Because of its economic impact and due to the animal welfare policy, the pathogenesis of this intramammary infection was studied extensively over the past 50 years. Still, the costs associated with the use of dairy cows for mastitis research constitute a major drawback. As an alternative, a mouse model of experimentally induced mastitis was developed some decades ago. This model has been increasingly used as it appears to be very suited for studying ruminant mastitis due to similarities between mice and cows. The various techniques for inducing mastitis in mice as well as the different pathogens and initial inoculum doses used are also compared in this review. Moreover, recent findings concerning the administration of antimicrobial and immunomodulatory agents are discussed. In addition, information is provided on the most novel approaches for the study of mastitis including the use of mutant pathogen strains and transgenic mice.

The pathogenesis and control of Staphylococcus aureus-induced mastitis: study models in the mouse

The intramammary colonisation by Staphylococcus aureus provokes mastitis in the cow. Once established, the infection is difficult to eradicate with available therapies and may become chronic. The present article focuses on the use of the experimental mouse model of S. aureus-induced mastitis as a practical approach for the study of bovine mastitis. Results obtained regarding the pathogenesis of S. aureus and the development of new therapeutic approaches are discussed.

Involvement of granulysin-producing T cells in the development of superficial microbial folliculitis

BACKGROUND

Granulysin is a recently identified antimicrobial protein expressed on cytotoxic T cells, natural killer (NK) cells and NKT cells. It has been shown that granulysin contributes to the defence mechanisms against mycobacterial infection. Superficial microbial folliculitis is a common skin disease. In a previous report, we showed that, as a first line of defence, alpha-defensin, a human neutrophil peptide, and beta-defensin (human beta-defensin-2) were expressed in infiltrating neutrophils and in lesional epidermal keratinocytes, respectively, in superficial folliculitis. As we also observed many infiltrating lymphocytes in lesional dermis, we hypothesized that infiltrating lymphocytes may possess antimicrobial substances, such as granulysin, and play a role in the defence mechanism as a second line of defence.

OBJECTIVES

Seven specimens of superficial microbial folliculitis diagnosed clinically and histologically were examined by means of immunohistochemistry. To identify the phenotype of cells expressing granulysin, confocal laser microscopic examination was performed.

RESULTS

A dense lymphoid cell infiltrate was observed in pustules, in the perivascular regions. A large number of these lymphoid cells were positive for granulysin. Phenotypically, cells consisted of CD3+ T cells, CD8+ T cells and UCHL-1+ T cells. CD20+ cells and CD56+ cells were not observed. Microscopic examination with a confocal laser showed that the lymphocytes producing granulysin were CD3+ and CD4+ T cells but not CD8+ T cells.

CONCLUSIONS

We showed that many granulysin-bearing T cells infiltrated affected follicles and perilesional dermis in superficial microbial folliculitis. However, few granulysin-positive lymphoid cells were observed in sterile pustular lesions. Our observations indicated that adaptive immunity such as granulysin, a lymphocyte-produced antimicrobial protein, may play an important role in the cutaneous defence mechanism.