Characterization of TLR2, NOD2, and related cytokines in mammary glands infected by Staphylococcus aureus in a rat model

Minthostachys verticillata essential oil modulates cytokine synthesis and Staphylococcus aureus internalization in MAC-T cells at least through TLR4/MyD88/NFkB pathway

The aim of this study was to evaluate the activation pathway(s) triggered by Minthostachys verticillata essential oil (EO) in bovine mammary epithelial cells (MAC-T) challenged with a strain of bovine Staphylococcus aureus. MAC-T cells were stimulated with EO, S. aureus or pre-treated with EO and then challenged with S. aureus. Cytokine's release was measured by ELISA. The mRNA for TLR2, TLR4, NOD2, MyD88 and NFκB was quantified by RT-qPCR. S. aureus adherence and internalization was also evaluated. MAC-T cells stimulated with S. aureus synthesized high levels of IL-1ß and IL-6 were kept up to 48 h, while IL-4 levels were not altered. Cells pre-treated with EO for 2 and 6 h and then challenged with S. aureus showed a significant increase of IL-1β and IL-6. However, in these cells, a decrease in IL-1ß and IL-6 levels and an increase of IL-4 values was observed from 24 h. No significant increase in the expression levels of TLR2 or NOD2 was detected in all stimulated cells. However, the expression of TLR4, MyD88 and NFκB was increased in cells stimulated with S. aureus at 2 and 6 h as well as in cells pre-treated with EO between 2 and 6 h and then challenged with S. aureus. The NFκB expression levels was similar to control at 24 h in all stimulated cells, although pro-inflammatory cytokine levels and TLR4 and MyD88 expression levels remained high in cells stimulated with S. aureus. This results suggested the activation of other pathways independent of MyD88 by the pathogen that involucrated the activation of others transcription factors. Pre-treatment with EO during 2, 6 and 24 h did not affect S. aureus adherence but decreased its internalization. In conclusion, pre-treatment with EO increased the IL-1β and IL-6 synthesis during the first hours post-challenged with S. aureus up-regulating TLR4/MyD88/NFκB pathway. Furthermore, EO increased the IL-4 levels from 6 to 24 h down-regulating the NFκB and possibly other transcription factors activated by the pathogen, which decreased its internalization into MAC-T cells.

Elevated muramyl dipeptide by sialic acid-facilitated postantibiotic pathobiont expansion contributes to gut dysbiosis-induced mastitis in mice

INTRODUCTION

In responses to antibiotics exposure, gut dysbiosis is a risk factor not only for pathogen infection but also for facilitating pathobiont expansion, resulting in increased inflammatory responses in the gut and distant organs. However, how this process is regulated has not been fully elucidated.

OBJECTIVES

In this study, we investigated the role of sialic acid, a host-derived carbohydrate, in the pathogenesis of gut dysbiosis-derived inflammation in distant organs.

METHODS

Ampicillin (Amp)-induced gut dysbiotic mice were treated with N-glycolylneuraminic acid (Neu5Gc) and N-acetylneuraminic acid (Neu5Ac) for three weeks to assess the role of sialic acids in mastitis. The underlying mechanism by which sialic acids regulate mastitis was explored using 16S rRNA sequencing, transcriptomics and employed multiple molecular approaches.

RESULTS

Administration of Neu5Ac and Neu5Gc exacerbated gut dysbiosis-induced mastitis and systemic inflammation. The gut dysbiosis caused by Amp was also aggravated by sialic acid. Notably, increased Enterococcus expansion, which was positively correlated with inflammatory markers, was observed in both Neu5Ac- and Neu5Gc-treated gut dysbiotic mice. Treatment of mice with Enterococcus cecorum (E. cecorum) aggravated gut dysbiosis-induced mastitis. Mechanically, sialic acid-facilitated E. cecorum expansion promoted muramyl dipeptide (MDP) release, which induced inflammatory responses by activating the NOD2-RIP2-NF-κB axis.

CONCLUSIONS

Collectively, our data reveal a role of sialic acid-facilitated postantibiotic pathobiont expansion in gut dysbiosis-associated inflammation, highlighting a potential strategy for disease prevention by regulating the MDP-NOD2-RIP2 axis.

The Application of Rat Models in Staphylococcus aureus Infections

Staphylococcus aureus (S. aureus) is a major human pathogen and can cause a wide range of diseases, including pneumonia, osteomyelitis, skin and soft tissue infections (SSTIs), endocarditis, mastitis, bacteremia, and so forth. Rats have been widely used in the field of infectious diseases due to their unique advantages, and the models of S. aureus infections have played a pivotal role in elucidating their pathogenic mechanisms and the effectiveness of therapeutic agents. This review outlined the current application of rat models in S. aureus infections and future prospects for rat models in infectious diseases caused by S. aureus.

Anti-inflammatory effects of chlorogenic acid from Taraxacum officinale on LTA-stimulated bovine mammary epithelial cells via the TLR2/NF-κB pathway

Mastitis is an inflammatory disease caused by microbial infection. Chlorogenic acid (CGA), one of the major phenolic acids in Taraxacum officinale, has natural antioxidant and anti-inflammatory properties in various cell types; however, the effects of CGA on Lipoteichoic acid (LTA)-induced bovine mammary epithelial cells (BMECs) have not been investigated. In this study, the CGA content in T. officinale was determined by High-performance liquid chromatography (HPLC). BMECs were infected with LTA to induce the mastitis model. Different concentrations of CGA were administered after establishing the LTA infection. The results showed that the T. officinale contained CGA 1.36 mg/g. CGA significantly reduced the pro-inflammatory gene and protein expression of TNF-α, IL-6, and IL-1β. In addition, CGA downregulated the NO, TLR2, and NF-κB signaling pathways in LTA-infected bovine mammary epithelial cells. Our results indicate that CGA reduced the expression of TNF-α, IL-6, IL-1β, and TLR2 by inhibiting the phosphorylation of proteins in the NF-κB signaling pathways in a dose-dependent manner. This finding suggests that CGA may be a potential agent for the treatment of mastitis in dairy cows.

Salvia miltiorrhiza polysaccharides ameliorates Staphylococcus aureus-induced mastitis in rats by inhibiting activation of the NF-κB and MAPK signaling pathways

The lactation capacity of dairy cows is critical to the productivity of the animals. Mastitis is a disease that directly affects the lactation capacity of cows. Staphylococcus aureus (S. aureus) is one of the most important pathogens that causes mastitis in dairy cows. The anti-inflammatory effect of Salvia miltiorrhiza polysaccharides (SMPs) has been demonstrated in mice and chickens. However, the effectiveness of SMPs in preventing and treating mastitis is unclear. Therefore, the purpose of this study was to explore the protective effect and mechanism of SMPs on mastitis caused by S. aureus. S. aureus was used to induce mastitis in rats, and three doses of SMPs (87.5, 175, 350 mg/kg, BW/d) were administered as treatments. The bacterial load, histopathology, and myeloperoxidase (MPO) and N-acetyl-β-D-glucosaminidase (NAGase) activities of mammary glands were observed and measured. Cytokines, including interleukin (IL)-1β, interleukin (IL)-6, and tumor necrosis factor α (TNF-α), were examined by qRT-PCR and ELISA. Key proteins in the NF-κB and MAPK signaling pathways were analyzed by Western blotting. The results showed that SMP supplementation could significantly reduce the colonization of S. aureus and the recruitment of inflammatory cells in mammary glands. S. aureus-induced gene transcription and protein expression of IL-1β, IL-6, and TNF-α were significantly suppressed in mammary glands. In addition, the increase in NF-κB and MAPK protein phosphorylation was inhibited by SMPs. These results revealed that supplementation with SMPs protected the mammary gland of rats against damage caused by S. aureus and alleviated the inflammatory response. This study provides a certain experimental basis for the treatment of S. aureus-induced mastitis with SMPs in the future.

Selenium Attenuates S. aureus-Induced Inflammation by Regulation TLR2 Signaling Pathway and NLRP3 Inflammasome in RAW 264.7 Macrophages

This study aimed to investigate the effects of selenium (Se) on the expression of Toll-like receptor (TLR) 2 and pyrin domain-containing protein (NLRP)3 inflammasome in macrophages infected by Staphylococcus aureus (S. aureus). RAW 264.7 macrophages were treated with 2 μmol/L Na2SeO3 for 12 h before infection with S. aureus for 2 h. Through Western blot, qRT-PCR, and ELISA analysis, the core molecules of TLR2 signaling pathway and NLRP3 inflammasome in RAW 264.7 macrophages were detected. Results showed that Se significantly reduced the elevated mRNA expression of TLR2, myeloid differentiation factor-88 (Myd88), NLRP3, Caspase-recruitment domain (ASC), and Caspase-1 induced by S. aureus. Furthermore, compared with I group, the protein expression of TLR2, Myd88, NLRP3, ASC, and Caspase-1 were suppressed in T group. In addition, the mRNA and protein expression of interleukin-1 beta (IL-1β) induced by S. aureus were also decreased after Se treatment. In conclusion, Se inhibits S. aureus-induced inflammation by suppressing the activation of the TLR2 signaling pathway and NLRP3 inflammasome in RAW 264.7 macrophages.

Taraxacum mongolicum protects against Staphylococcus aureus-infected mastitis by exerting anti-inflammatory role via TLR2-NF-κB/MAPKs pathways in mice

ETHNOPHARMACOLOGICAL RELEVANCE

As a traditional Chinese medicine, Taraxacum mongolicum has been widely used for the prevention and treatment of a variety of inflammatory and infectious diseases, and also clinically used as a remedy for mastitis. However, the scientific rationale and mechanism behind its use on mastitis in vivo are still unclear.

AIM OF THE STUDY

This study aimed to investigate the protective effect and potential mechanism of Taraxacum mongolicum Hand.-Mazz. (T. mongolicum) on mastitis infected by Staphylococcus aureus (S. aureus).

MATERIALS AND METHODS

Female ICR mice were given intragastrically 2.5, 5 and 10 g/kg of T. mongolicum extract twice per day for 6 consecutive days, and infected with S. aureus via teat canal to induce mastitis. Pro-inflammatory cytokine tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β) levels were determined by ELISA. Myeloperoxidase (MPO) activity and distribution were measured by reagent kit and immunohistochemistry. Histopathological changes of mammary gland tissues were observed by H&E staining. Toll-like receptor 2 (TLR2) expression, phosphorylations of related proteins in nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinases (MAPKs) signaling pathways were detected by western blot.

RESULTS

T. mongolicum decreased TNF-α, IL-6 and IL-1β levels, and reduced MPO activity and distribution in sera and mammary glands with S. aureus-infected mastitis. In addition, T. mongolicum effectively attenuated histopathological damages and cell necrosis of mammary gland tissues infected by S. aureus. Moreover, T. mongolicum inhibited the expression of TLR2, and the phosphorylations of inhibitor κBα (IκBα), p65, p38, extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK) proteins in mammary glands with S. aureus-infected mastitis.

CONCLUSIONS

This study suggests that T. mongolicum protects against S. aureus-infected mastitis by exerting anti-inflammatory role, which is attributed to the inhibition of TLR2-NF-κB/MAPKs pathways.

Hederacoside-C Inhibition of Staphylococcus aureus-Induced Mastitis via TLR2 & TLR4 and Their Downstream Signaling NF-κB and MAPKs Pathways In Vivo and In Vitro

Hederacoside-C (HDC) is a biological active ingredient, extracted from the leaves of Hedera helix. It has been reported to have anti-inflammatory properties. However, the effects of HDC on Staphylococcus aureus (S. aureus)-induced mastitis have not been reported yet. Here, we evaluated the anti-inflammatory effects of HDC on S. aureus-induced mastitis both in vivo on mammary gland tissues and in vitro on RAW 264.7 cells. The ascertained histopathological changes and MPO activity revealed that HDC defended mammary glands from tissue destruction and inflammatory cell infiltration induced by S. aureus. The results of ELISA, western blot, and qRT-PCR indicated that HDC significantly inhibited the expressions IL-6, IL-1β, and TNF-α and enhanced the IL-10 by downregulating and upregulating their relevant genes, respectively. Furthermore, HDC markedly suppressed the TLR2 and TLR4 expressions by attenuating the MAPKs (p38, ERK, JNK) and NF-κB (p65 and IκBα) pathways followed by decreasing the phosphorylation of p38, ERK, JNK, p65, and IκBα. The above parameters enhanced the mammary gland defense and reduced inflammation. These findings suggested that HDC may have the potential to be an effective anti-inflammatory drug for the S. aureus-induced mice mastitis and in RAW 264.7 cells.

Selenium Plays an Anti-Inflammatory Role by Regulation NLRP3 Inflammasome in Staphylococcus aureus-Infected Mouse Mammary Gland

Selenium is an essential micronutrient that plays an important role in immunity. However, the mechanism that Selenium modulates mastitis is not fully clear. In this experiment, we investigated whether selenium can inhibit the activation of the NLRP3 inflammasome in a mouse model of Staphylococcus aureus-induced mastitis. Eighty BALB/c female mice were fed with experimental Selenium deficiency basal diet for 2 weeks to achieve the purpose of selenium consumption until pregnancy. Pregnant mice were randomly divided into four groups (control group; selenium supplement group; Staphylococcus aureus infection group and Staphylococcus aureus infection after selenium supplement group). Twenty-four hours after challenging, all mice were euthanized and mammary tissue samples were aseptically collected. Through pathological staining, western blot analysis, real-time fluorescence quantitative polymerase chain reaction analysis, and enzyme-linked immunosorbent assay, the regulation effect of Selenium on NLRP3 inflammasome was detected. The result showed that compared with the control group, selenium significantly inhibited the expression of NLRP3, ASC, Caspase-1, Caspase-1 p20, and Pro-IL-1β (p < 0.01). Meanwhile the mRNA expression and release of IL-1β was suppressed in the treatment group compared with Staphylococcus aureus infection group (p < 0.01). Therefore, these results suggest that dietary selenium can attenuate Staphylococcus aureus mastitis by inhibition of the NLRP3 inflammasome.

Staphylococcus aureus induces mammary gland fibrosis through activating the TLR/NF-κB and TLR/AP-1 signaling pathways in mice

To investigate the TLR-NF-κB/AP-1 pathways in S. aureus infection-induced mammary gland fibrosis, mice were infected with S. aureus isolated from the mammary glands of cows with mastitis. Lactating mice were divided into three groups: control group (CON); PBS control group (PBS) and the S. aureus-treated group (S. aureus). Pathological observations revealed that neutrophil infiltration into mammary gland tissue was obviously induced by S. aureus at the early stage of infection (1-7 d). With persistent S. aureus infection, mammary gland fibrosis developed and was characterized by infiltration and proliferation of macrophage, lymphocyte and fibroblast and ECM hyperplasia (7-21 d). Immunohistochemistry staining showed upregulation of fibrosis associated cytokines viz bFGF and PDGF-BB. Real-time qPCR and Western blot analysis revealed that transcription and translation of TLR2, TLR4, bFGF, PDGF-BB, α-SMA and COL Ⅰ α1 was significantly upregulated by S. aureus. NF-κB p65 and AP-I c-jun were translocated into the nucleus after S. aureus infection. There was no remarkable difference between the CON and PBS groups. The datas indicate that mammary gland fibrosis in mice is induced by S. aureus, which promotes cytokine release and the expression of ECM though activating the TLR/NF-κB p65 and TLR/AP-1 c-jun signaling pathways.

Organic Selenium Ameliorates Staphylococcus aureus-Induced Mastitis in Rats by Inhibiting the Activation of NF-κB and MAPK Signaling Pathways

Mastitis is an economically important disease in dairy cows, which is often caused by Staphylococcus aureus (S. aureus). Selenium is an indispensable element for physiological function and contributes to reduce injury of the mammary glands in mastitis. However, adequate sources of selenium have always been an important consideration for livestock. Therefore, the study aimed to explore the protective effect and mechanism of Selenohomolanthionine (SeHLan) on mastitis induced by S. aureus. The S. aureus-induced rat model was established and three doses (0.2, 2, 20 μg/kg body weight/day) of dietary OS were supplemented. The bacterial load, histopathology, and myeloperoxidase (MPO) of the mammary glands were performed and determined. Cytokines, including interleukin (IL)-1β, TNF-α, and IL-6, were detected using qRT-PCR. The key proteins of NF-κB and MAPK signaling pathways were analyzed by Western blot. The results revealed that OS supplementation could reduce the recruitment of neutrophils and macrophages in mammary tissues, but did not decrease S. aureus load in the tissues. The overexpression levels of IL-1β, TNF-α, and IL-6 induced by S. aureus were inhibited after OS treatment. Furthermore, the increased phosphorylation of NF-κB and MAPKs proteins were also suppressed. The results suggest that dietary supplementation with adequate OS during pregnancy contributes to protect the mammary glands from injury caused by S. aureus and alleviate the inflammatory response.

Staphylococcus aureus-induced proteomic changes in the mammary tissue of rats: A TMT-based study

Staphylococcus aureus is one of the most important pathogens causing mastitis in dairy cows. The objective of this study was to establish a rat model of mastitis induced by S. aureus infection and to explore changes in the proteomes of mammary tissue in different udder states, providing a better understanding of the host immune response to S. aureus mastitis. On day 3 post-partum, 6 rats were randomly divided into two groups (n = 3), with either 100 μL of PBS (blank group) or a S. aureus suspension containing 2×10⁷ CFU·mL⁻¹ (challenge group) infused into the mammary gland duct. After 24 h of infection, the rats were sacrificed, and mammary gland tissue was collected. Tandem mass tag (TMT)-based technology was applied to compare the proteomes of healthy and mastitic mammary tissues. Compared with the control group, the challenge group had 555 proteins with significant differences in expression, of which 428 were significantly upregulated (FC>1.2 and p<0.05) and 127 were downregulated (FC>0.83 and p<0.05 or p<0.01). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that upregulated differentially significant expressed proteins (DSEPs) were associated with mainly immune responses, including integrin alpha M, inter-α-trypsin inhibitor heavy chain 4, and alpha-2-macroglobulin. This study is the first in which a rat model of S. aureus-induced mastitis was used to explore the proteins related to mastitis in dairy cows by TMT technology, providing a model for replication of dairy cow S. aureus-induced mastitis experiments.

Periodic vicissitudes of different concentrations of a developed prototype killed S. aureus mastitis vaccine on immune modulators, mediators and immunoglobulins in cows

Mastitis is the inflammation of the mammary gland due to microbial infiltration causing a reduced mammary function. This study aims at developing a vaccine using Malaysian local isolate of Staphylococcus aureus and evaluating serum amyloid A, Interleukin-10, IgM and IgG responses periodically. Four bacterin concentrations (10⁶, 10⁷, 10⁸ and 10⁹ cfu/ml of the local isolate of S. aureus) were adjuvanted with aluminium potassium sulphate. Thirty cows grouped into 4 treatment groups (G-) were vaccinated (2 ml) intramuscularly, with a fifth G-A as control. The mean concentration (MC) of serum amyloid A (SAA) was significantly different (sig-d) (p ˂ 0.05) in G-D at 0 h post vaccination (PV), 3 h PV, 24 h PV, weeks 1, 2, 3 and 4 PV (6-, 15-, 5-, 12-, 11-, 4- and 11-fold increased (FI) respectively). The MC of serum amyloid A was also sig-d in G-E at 0 h PV, weeks 1, 2 and 4 PV (3, 8, 5 and 8 FI respectively). The MC of IL-10 was sig-d in G-D and C at 3 h PV and week 2 PV (5 and 2 FI respectively). The IgM MC was sig-d in G-B and C at 3 h PV (5 and 6 FI respectively), at 24 h PV (5 and 9 FI respectively), at week 3 PV(2 and 2 FI respectively) and week 4 PV (3 and 4 FI respectively). The MC of IgG was sig-d in G-E at 0 h, 3 h and week 3 PV(5, 6 and 2 FI respectively) and in G-D at weeks 1-4 (3, 3, 3 and 5 FI respectively). In conclusion, elevated levels of SAA, IgG and IL-10 in G-D(10⁸) informed our choice of best dosage which can be used to evoke immunity in cows.

Staphylococcus aureus modulation of innate immune responses through Toll-like (TLR), (NOD)-like (NLR) and C-type lectin (CLR) receptors

Early recognition of pathogens by the innate immune system is crucial for bacterial clearance. Many pattern recognition receptors (PRRs) such as Toll-like (TLRs) and (NOD)-like (NLRs) receptors have been implicated in initial sensing of bacterial components. The intracellular signaling cascades triggered by these receptors result in transcriptional upregulation of inflammatory pathways. Although this step is crucial for bacterial elimination, it is also associated with the potential for substantial immunopathology, which underscores the need for tight control of inflammatory responses. The leading human bacterial pathogen Staphylococcus aureus expresses over 100 virulence factors that exert numerous effects upon host cells. In this manner, the pathogen seeks to avoid host recognition or perturb PRR-induced innate immune responses to allow optimal survival in the host. These immune system interactions may result in enhanced bacterial proliferation but also provoke systemic cytokine responses associated with sepsis. This review summarizes recent findings on the various mechanisms applied by S. aureus to modulate or interfere with inflammatory responses through PRRs. Detailed understanding of these complex interactions can provide new insights toward future immune-stimulatory therapeutics against infection or immunomodulatory therapeutics to suppress or correct dysregulated inflammation.

Selenium ameliorates Staphylococcus aureus-induced inflammation in bovine mammary epithelial cells by inhibiting activation of TLR2, NF-κB and MAPK signaling pathways

BACKGROUND

Staphylococcus aureus (S. aureus) internalization into bovine mammary epithelial cells (bMECs) is considered an important pathogenic mechanism for the establishment of mastitis. Given the interesting link between selenium (Se) status and mastitis, our objective was to prove that Se was essential to suppress pro-inflammatory mediators, in part, by modulation of Toll-like receptor2 (TLR2), nuclear factor kappaB (NF-κB) and mitogen activated protein kinase (MAPK) signal transduction pathway in bMECs.

RESULTS

Results showed that Se (0~ 16 μM) did not affect the growth of bMECs. The mRNA expression of TLR2, Myeloid differentiation factor 88 (Myd88), Interleukin-1 receptor-associated kinase4 (Irak4), Interleukin-1 receptor-associated kinase1 (Irak1) and TNF receptor-associated factor6 (Traf6) in TLR2 signal pathway were increased or significantly increased by S. aureus. Se played an important role in regulating the genes expression of TLR2, Myd88, Traf6 but not in controlling the expression of Irak4 and Irak1. In addition, Se exerted strong inhibitory effects on the genes expression of tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) induced by S. aureus. To further investigate the possible signaling mechanisms involved in the processes, we analyzed the role of MAPK and NF-κB signaling pathway in inflammation response in S. aureus-stimulated bMECs in vitro. Results showed that the phosphorylation of inhibitory kappaB alpha (IκBα), p65, p38 and extracellular regulated protein kinase (Erk) were significantly increased in S. aureus-stimulated bMECs. It indicated that S. aureus activated NF-κB and MAPK signaling pathway. We also examined the effects of Se on the phosphorylation of IκBα, p65, p38 and Erk in NF-κB and MAPK signaling pathway, which have well been proved to control the synthesis and release of pro-inflammatory mediators during inflammation. The findings are exciting, that pretreatment with Se (4, 8 μM) significantly suppressed the phosphorylation of IκBα, p65, p38 and Erk.

CONCLUSIONS

These results suggest that Se down-regulates inflammatory mediators TNF-α, IL-1β and IL-6 gene expressions via TLR2, NF-κB and MAPK signaling pathway in S. aureus-stimulated bMECs, which may be responsible for the anti-inflammatory effect of Se.

Preconditioning with Lipopolysaccharide or Lipoteichoic Acid Protects against Staphylococcus aureus Mammary Infection in Mice

Staphylococcus aureus is one of the most causative agents of mastitis and is associated with chronic udder infections. The persistency of the pathogen is believed to be the result of an insufficient triggering of local inflammatory signaling. In this study, the preclinical mastitis model was used, aiming to evaluate if lipopolysaccharide (LPS) or lipoteichoic acid (LTA) preconditioning could aid the host in more effectively clearing or at least limiting a subsequent S. aureus infection. A prototypic Gram-negative virulence factor, i.e., LPS and Gram-positive virulence factor, i.e., LTA were screened whether they were able to boost the local immune compartment. Compared to S. aureus-induced inflammation, both toxins had a remarkable high potency to efficiently induce two novel selected innate immunity biomarkers i.e., lipocalin 2 (LCN2) and chitinase 3-like 1 (CHI3L1). When combining mammary inoculation of LPS or LTA prior to a local S. aureus infection, we were able to modulate the innate immune response, reduce local bacterial loads, and induce either LCN2 or CHI3L1 at 24 h post-infection. Clodronate depletion of mammary macrophages also identified that macrophages contribute only to a limited extend to the LPS/LTA-induced immunomodulation upon S. aureus infection. Based on histological neutrophil influx evaluation, concomitant local cytokine profiles and LCN2/CHI3L1 patterns, the macrophage-independent signaling plays a major role in the LPS- or LTA-pretreated S. aureus-infected mouse mammary gland. Our results highlight the importance of a vigilant microenvironment during the innate immune response of the mammary gland and offer novel insights for new approaches concerning effective immunomodulation against a local bacterial infection.

Intramammary inoculation of Panax ginseng plays an immunoprotective role in Staphylococcus aureus infection in a murine model

The immunoprotective effect of Panax ginseng (Pg) extract was investigated in a mouse mastitis model. Lactating female mice were intramammarily inoculated with Pg or placebo, and then were challenged with S. aureus, while other group was inoculated with S. aureus alone. The number of bacteria recovered from mammary glands was significantly lower in Pg-treated S. aureus-infected mice (group I) compared with placebo-treated S. aureus-infected mice (group II) and S. aureus-infected mice (group III). The mRNA expression of TLR2, TLR4, IL-1α and TNF-α was influenced by treatment; being the transcript levels for all genes higher in group I compared with group II and III. Activation of NF-κB and the number of monocytes-macrophages in mammary gland tissue was significantly increased in group I compared with group II and III. Pg extract was able to trigger an adequate immune response to confront an infection demonstrating its protective effect and potential for preventing bovine intramammary infections.

Immune response of Staphylococcus aureus strains in a mouse mastitis model is linked to adaptive capacity and genotypic profiles

Staphylococcus aureus is one of the most frequently isolated major pathogens from intramammary infections (IMI) worldwide. The mechanisms by which S. aureus IMI are established and maintained in dairy cows involve both bacterial escape strategies and modulation of the host immune response. Moreover, it was shown that different S. aureus strains have varying effects on the immune response. The aim of this study was to investigate the immune response in a mouse mastitis model of two S. aureus strains isolated from bovine IMI with different clinical manifestation (persistent-P or non-persistent-NP), phenotypic and genotypic profile. Both strains were capable of establishing an IMI after 264h post inoculation (pi). Strain A (NP) showed a more aggressive behaviour than strain B (P) at early stages of IMI, while strain B multiplied initially at a lower rate but increased its replication capacity from 120h pi to the end of the study (264h pi). Strain A triggered a stronger initial inflammatory response compared with strain B inducing higher gene and protein expression of TLR2, NF-κB activation and higher gene expression of IL-1α at initial stage of IMI (6-12h pi) but inducing extensive mammary tissue damage. Immune cells response was different for each S. aureus strain throughout the course of infection, showing mammary glands inoculated with strain A greater initial immune cells stimulation compared with strain B and then a second immune cells stimulation (from 120 to 264h pi) represented by monocytes-macrophages, T and B lymphocytes, mainly stimulated by strain B, consistent with inflammatory process becoming chronic. Strain-specific pathogenicity observed underscores the importance of pathogen factors in the progression of the infectious process. These results contribute to increase the available information on host-pathogen interaction and point out for the need of further research to expand the knowledge about these interactions for developing new strategies to intervene in the IMI progress.

Anti-Inflammatory Activity of the Essential Oil Citral in Experimental Infection with Staphylococcus aureus in a Model Air Pouch

This study proposes to implement an alternative and effective strategy for local treatment of disease provoked by S. aureus. For the analysis of possible anti-inflammatory activity of essential oil, after establishing an air pouch model, 48 male mice of Balb/c were treated, infected, and euthanized at 4 and 8 h. Thus, the total and differential white blood cells were counted in the animal's blood, and cytokines IL-1β, IL-6, and TNF-α were titrated using ELISA in the air pouch lavage. Moreover, TNF-α, IL-1β, and IL-6 gene expression was analyzed through an RT-qPCR array, and S. aureus was quantified using qPCR. Our results, p < 0.05, showed that EOC reduced the quantity of microorganisms. The group of mice treated with essential oil citral showed a significant decrease in TNF-α levels in tests demonstrating anti-inflammatory activity. There is no data about the mutual influence of the air pouch model, essential oil citral, and S. aureus. Thus, considering the interaction of these variables and the anti-inflammatory activity of the essential oil citral, we demonstrated, by alternative local treatment, a new antimicrobial agent that is not an antibiotic.