Staphylococcal enterotoxin H induced apoptosis of bovine mammary epithelial cells in vitro

Staphylococcal Enterotoxins: Description and Importance in Food

Staphylococcus aureus stands out as one of the most virulent pathogens in the genus Staphylococcus. This characteristic is due to its ability to produce a wide variety of staphylococcal enterotoxins (SEs) and exotoxins, which in turn can cause staphylococcal food poisoning (SFP), clinical syndromes such as skin infections, inflammation, pneumonia, and sepsis, in addition to being associated with the development of inflammation in the mammary glands of dairy cattle, which results in chronic mastitis and cell necrosis. SEs are small globular proteins that combine superantigenic and emetic activities; they are resistant to heat, low temperatures, and proteolytic enzymes and are tolerant to a wide pH range. More than 24 SE genes have been well described (SEA-SEE, SEG, SEH, SEI, SEJ, SElK, SElL, SElM, SElN, SElO, SElP, SElQ, SElR, SElS, SElT, SElU, SElV, SElW, SElX, SElY, and SElZ), being a part of different SFP outbreaks, clinical cases, and isolated animal strains. In recent years, new genes (sel26, sel27, sel28, sel31, sel32, and sel33) from SEs have been described, as well as two variants (seh-2p and ses-3p) resulting in a total of thirty-three genes from Ses, including the nine variants that are still in the process of genetic and molecular structure evaluation. SEs are encoded by genes that are located in mobile genetic elements, such as plasmids, prophages, pathogenicity islands, and the enterotoxin gene cluster (egc), and housed in the genomic island of S. aureus. Both classical SEs and SE-like toxins (SEls) share phylogenetic relationships, structure, function, and sequence homology, which are characteristics for the production of new SEs through recombination processes. Due to the epidemiological importance of SEs, their rapid assessment and detection have been crucial for food security and public health; for this reason, different methods of identification of SEs have been developed, such as liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS), molecular methods, and whole-genome sequencing; providing the diagnosis of SEs and a better understanding of the occurrence, spread, and eradication of SEs. This review provides scientific information on the enterotoxins produced by S. aureus, such as structural characteristics, genetic organization, regulatory mechanisms, superantigen activity, mechanisms of action used by SEs at the time of interaction with the immune system, methods of detection of SEs, and recent biocontrol techniques used in food.

The Yeast and Hypha Phases of Candida krusei Induce the Apoptosis of Bovine Mammary Epithelial Cells via Distinct Signaling Pathways

Infection with Candida spp. is a significant cause of bovine mastitis globally. We previously found that C. krusei was the main pathogen causing mycotic mastitis in dairy cows in Yinchuan, Ningxia, China. However, whether the infection of this pathogen could induce apoptosis in BMECs remained unclear. In this report, we explored the apoptosis and underlying mechanism of BMECs induced by C. krusei yeast and hypha phases using a pathogen/host cell co-culture model. Our results revealed that both the yeast and hypha phases of C. krusei could induce BMEC apoptosis; however, the yeast phase induced more cell apoptosis than the hypha phase, as assessed via electronic microscopy and flow cytometry assays. This finding was further corroborated via the measurement of the mitochondrial membrane potential (MMP) and the TUNEL test. Infection by both the yeast and hypha phases of C. krusei greatly induced the expression of proteins associated with cell death pathways and important components of toll-like receptor (TLR) signaling, including TLR2 and TLR4 receptors, as determined via a Western blotting assay. BMECs mainly underwent apoptosis after infection by the C. krusei yeast phase through a mitochondrial pathway. Meanwhile, BMEC apoptosis induced by the C. krusei hypha phase was regulated by a death ligand/receptor pathway. In addition, C. krusei-induced BMEC apoptosis was regulated by both the TLR2/ERK and JNK/ERK signaling pathways. These data suggest that the yeast phase and hypha phase of C. krusei induce BMEC apoptosis through distinct cell signaling pathways. This study represents a unique perspective on the molecular processes underlying BMEC apoptosis in response to C. krusei infection.

Staphylococcal Enterotoxins Promote Virulence in Bacterial Keratitis

Purpose

Staphylococcus aureus is an important cause of corneal infections (keratitis). To better understand the virulence mechanisms mediating keratitis, a recent comparative genomics study revealed that a set of secreted enterotoxins were found with higher prevalence among ocular versus non-ocular S. aureus clinical infection isolates, suggesting a key role for these toxins in keratitis. Although well known to cause toxic shock syndrome and S. aureus food poisoning, enterotoxins have not yet been shown to mediate virulence in keratitis.

Methods

A set of clinical isolate test strains, including a keratitis isolate that encodes five enterotoxins (sed, sej, sek, seq, ser), its corresponding enterotoxin deletion mutant and complementation strain, a keratitis isolate devoid of enterotoxins, and the non-ocular S. aureus strain USA300 along with its corresponding enterotoxin deletion and complementation strains, were evaluated for cellular adhesion, invasion and cytotoxicity in a primary corneal epithelial model as well as with microscopy. Additionally, strains were evaluated in an in vivo model of keratitis to quantify enterotoxin gene expression and measure disease severity.

Results

We demonstrate that, although enterotoxins do not impact bacterial adhesion or invasion, they do elicit direct cytotoxicity in vitro toward corneal epithelial cells. In an in vivo model, sed, sej, sek, seq, ser were found to have variable gene expression across 72 hours of infection and test strains encoding enterotoxins resulted in increased bacterial burden as well as a reduced host cytokine response.

Conclusions

Our results support a novel role for staphylococcal enterotoxins in promoting virulence in S. aureus keratitis.

A culture-, amplification-independent, and rapid method for identification of pathogens and antibiotic resistance profile in bovine mastitis milk

Introduction

Rapid and accurate diagnosis of causative pathogens in mastitis would minimize the imprudent use of antibiotics and, therefore, reduce the spread of antimicrobial resistance. Whole genome sequencing offers a unique opportunity to study the microbial community and antimicrobial resistance (AMR) in mastitis. However, the complexity of milk samples and the presence of a high amount of host DNA in milk from infected udders often make this very challenging.

Methods

Here, we tested 24 bovine milk samples (18 mastitis and six non-mastitis) using four different commercial kits (Qiagens' DNeasy^® PowerFood^® Microbial, Norgens' Milk Bacterial DNA Isolation, and Molzyms' MolYsis™ Plus and Complete5) in combination with filtration, low-speed centrifugation, nuclease, and 10% bile extract of male bovine (Ox bile). Isolated DNA was quantified, checked for the presence/absence of host and pathogen using PCR and sequenced using MinION nanopore sequencing. Bioinformatics analysis was performed for taxonomic classification and antimicrobial resistance gene detection.

Results

The results showed that kits designed explicitly for bacterial DNA isolation from food and dairy matrices could not deplete/minimize host DNA. Following using MolYsis™ Complete 5 + 10% Ox bile + micrococcal nuclease combination, on average, 17% and 66.5% of reads were classified as bovine and Staphylococcus aureus reads, respectively. This combination also effectively enriched other mastitis pathogens, including Escherichia coli and Streptococcus dysgalactiae. Furthermore, using this approach, we identified important AMR genes such as Tet (A), Tet (38), fosB-Saur, and blaZ. We showed that even 40 min of the MinION run was enough for bacterial identification and detecting the first AMR gene.

Conclusion

We implemented an effective method (sensitivity of 100% and specificity of 92.3%) for host DNA removal and bacterial DNA enrichment (both gram-negative and positive) directly from bovine mastitis milk. To the best of our knowledge, this is the first culture- and amplification-independent study using nanopore-based metagenomic sequencing for real-time detection of the pathogen (within 5 hours) and the AMR profile (within 5-9 hours), in mastitis milk samples. These results provide a promising and potential future on-farm adaptable approach for better clinical management of mastitis.

Exploring the Role of Staphylococcus aureus in Inflammatory Diseases

Staphylococcus aureus is a very common Gram-positive bacterium, and S. aureus infections play an extremely important role in a variety of diseases. This paper describes the types of virulence factors involved, the inflammatory cells activated, the process of host cell death, and the associated diseases caused by S. aureus. S. aureus can secrete a variety of enterotoxins and other toxins to trigger inflammatory responses and activate inflammatory cells, such as keratinocytes, helper T cells, innate lymphoid cells, macrophages, dendritic cells, mast cells, neutrophils, eosinophils, and basophils. Activated inflammatory cells can express various cytokines and induce an inflammatory response. S. aureus can also induce host cell death through pyroptosis, apoptosis, necroptosis, autophagy, etc. This article discusses S. aureus and MRSA (methicillin-resistant S. aureus) in atopic dermatitis, psoriasis, pulmonary cystic fibrosis, allergic asthma, food poisoning, sarcoidosis, multiple sclerosis, and osteomyelitis. Summarizing the pathogenic mechanism of Staphylococcus aureus provides a basis for the targeted treatment of Staphylococcus aureus infection.

Diversity and pathogenesis of Staphylococcus aureus from bovine mastitis: current understanding and future perspectives

Staphylococcus aureus is a leading cause of bovine mastitis worldwide. Despite some improved understanding of disease pathogenesis, progress towards new methods for the control of intramammary infections (IMI) has been limited, particularly in the field of vaccination. Although herd management programs have helped to reduce the number of clinical cases, S. aureus mastitis remains a major disease burden. This review summarizes the past 16 years of research on bovine S. aureus population genetics, and molecular pathogenesis that have been conducted worldwide. We describe the diversity of S. aureus associated with bovine mastitis and the geographical distribution of S. aureus clones in different continents. We also describe studies investigating the evolution of bovine S. aureus and the importance of host-adaptation in its emergence as a mastitis pathogen. The available information on the prevalence of virulence determinants and their functional relevance during the pathogenesis of bovine mastitis are also discussed. Although traits such as biofilm formation and innate immune evasion are critical for the persistence of bacteria, the current understanding of the key host-pathogen interactions that determine the outcome of S. aureus IMI is very limited. We suggest that greater investment in research into the genetic and molecular basis of bovine S. aureus pathogenesis is essential for the identification of novel therapeutic and vaccine targets.

Staphylococcus aureus from Minas Artisanal Cheeses: Biocide Tolerance, Antibiotic Resistance and Enterotoxin Genes

Staphylococcus aureus is a common contaminant in artisanal raw-milk cheeses. Tolerance of S. aureus to biocides is a threat to disinfection in the cheese production environment, while antibiotic resistance and enterotoxin production are additional health concerns. This study aimed to evaluate the tolerance of S. aureus isolated from Minas artisanal cheeses to the biocides benzalkonium chloride, hexadecylpyridinium chloride, cetrimide, triclosan, hexachlorophene, and chlorhexidine, and the simultaneous occurrence of genes coding for antibiotic resistance (mecA, aacA-aphD, and tetK), efflux pumps [qacA/B and smr (qacC/D)], and enterotoxins (sea, seb, sec, sed, see, seg, seh, sei, and sej). Among the tested isolates, 38.2% were resistant to at least one biocide, and 73.1% were positive for one or more antibiotic resistance gene. Most of the biocide-tolerant and antibiotic-resistant isolates harbored efflux pump genes, and were positive for at least one staphylococcal enterotoxin gene. The study highlights the need for correct hygiene monitoring programs to ensure the safety of these products.

Anti-Staphylococcus aureus Single-Chain Fragment Variables Play a Protective Anti-Inflammatory Role In Vitro and In Vivo

Staphylococcus aureus is a causative agent of bovine mastitis, capable of causing significant economic losses to the dairy industry worldwide. This study focuses on obtaining single-chain fragment variables (scFvs) against the virulence factors of S. aureus and evaluates the protective effect of scFvs on bovine mammary epithelial (MAC-T) cells and mice mammary gland tissues infected by S. aureus. After five rounds of bio-panning, four scFvs targeting four virulence factors of S. aureus were obtained. The complementarity-determining regions (CDRs) of these scFvs exhibited significant diversities, especially CDR3 of the VH domain. In vitro, each of scFvs was capable of inhibiting S. aureus growth and reducing the damage of MAC-T cells infected by S. aureus. Preincubation of MAC-T cells with scFvs could significantly attenuate the effect of apoptosis and necrosis compared with the negative control group. In vivo, the qPCR and ELISA results demonstrated that scFvs reduced the transcription and expression of Tumor Necrosis Factor alpha (TNF-α), interleukin-1β (IL-1β), IL-6, IL-8, and IL-18. Histopathology and myeloperoxidase (MPO) results showed that scFvs ameliorated the histopathological damages and reduced the inflammatory cells infiltration. The overall results demonstrated the positive anti-inflammatory effect of scFvs, revealing the potential role of scFvs in the prevention and treatment of S. aureus infections.

miR-142-5p regulates lipopolysaccharide-induced bovine epithelial cell proliferation and apoptosis via targeting BAG5

Bovine mastitis is a threat to the health of the dairy cow. MicroRNAs (miRs) serve an important role in the progression of bovine mastitis, regulating immune and defense responses. The present study aimed to investigate the possible effects and mechanisms of bovine mastitis underlying miR-142-5p and Bcl-2 associated athanogene 5 (BAG5) in in vitro lipopolysaccharide (LPS)-induced models. Reverse transcription-quantitative PCR and western blotting were performed to determine mRNA and protein expression levels, respectively. ELISAs were conducted to assess the levels of cytokines and an immunofluorescence assay was performed to determine the expression of BAG5. Cell Counting Kit-8, clone formation and 5-ethynyl-2'-deoxyuridine assays were conducted to determine cell viability and proliferation of bovine mammary epithelial MAC-T cells, respectively. Flow cytometry was performed to measure MAC-T cell cycle distribution and apoptosis, and a luciferase assay was conducted to verify whether BAG5 was a target of miR-142-5p. The results indicated that miR-142-5p was upregulated in MAC-T cells treated with LPS compared with the control group. miR-142-5p mimics transfection significantly activated the cytokines TNF-α, IL-1β, IL-6 and IL-8, and significantly increased the expression levels of NF-κB signaling pathway-related proteins in LPS-treated cells. The luciferase activity of MAC-T cells treated with miR-142-5p mimics and BAG5 3'untranslated region wild type decreased, compared with mutant type. By contrast, BAG5 overexpression significantly downregulated the levels of cytokines, including TNF-α, IL-1β, IL-6 and IL-8, in LPS-treated cells. BAG5 overexpression significantly promoted cell proliferation and viability, decreased apoptosis, and regulated Caspase-3, Caspase-9, Bcl-2 and Bax expression in LPS-treated MAC-T cells, which was significantly reversed by transfection with miR-142-5p mimics. In conclusion, the results of the present study suggested that miR-142-5p may promote the progression of bovine mastitis via targeting BAG5. Therefore, the present study provided the foundations for future investigations.

Intracellular Staphylococcus aureus and host cell death pathways

Staphylococcus aureus is a major opportunistic human pathogen that is globally prevalent. Although S. aureus and humans may have co-evolved to the point of commensalism, the bacterium is equipped with virulence factors causing devastating infections. The adoption of an intracellular lifestyle by S. aureus is an important facet of its pathogenesis. Occupying a privileged intracellular compartment permits evasion from the bactericidal actions of host immunity and antibiotics. However, this localization exposes S. aureus to cell-intrinsic processes comprising autophagy, metabolic challenges and clearance mechanisms orchestrated by host programmed cell death pathways (PCDs), including apoptosis, pyroptosis and necroptosis. Mounting evidence suggests that S. aureus deploys pathoadaptive mechanisms that modulate the expression of its virulence factors to prevent elimination through PCD pathways. In this review, we critically analyse the current literature on the interplay between S. aureus virulence factors with the key, intertwined nodes of PCD. We discuss how S. aureus adaptation to the human host plays an essential role in the evasion of PCD, and we consider future directions to study S. aureus-PCD interactions.

Impacts of the Staphylococcal Enterotoxin H on the Apoptosis and lncRNAs in PC3 and ACHN

Cancer is considered as the most lethal disease for human beings, and up to now many attempts were failed for prevention and treatment of this tremendous health problem. Consequently, this study purpose was to investigate novel therapeutic methods for cancer. The bacterial toxin can result in cell death throughout the induction of apoptosis in cancer cell lines. We evaluated apoptosis and the expression levels of long non-coding RNAs (lncRNAs) in PC3, ACHN and HDF cell lines that were transfected with pCDNA3.1(+)-seh and empty plasmid. pCDNA3.1(+)-seh treatment showed overexpression of GAS5 (p = 0.0033 and p = 0.0033) in PC3 and ACHN cells, down regulation of PCA3 and NEAT1 (p = 0.0092 and p = 0.0097) in the PC3 cells, and down regulation of PVT1 and MALAT1 (p = 0.0239 and p = 0.0133) in the ACHN cells in comparison with the empty plasmid, but there was no significant effect on HDF normal cells. Additionally, this study data demonstrated that the cell adhesion was down regulated. The flow cytometry data showed transfection by pCDNA3.1 (+)-seh could elevate PC3 and ACHN cell apoptosis levels in comparison with empty plasmid. This study findings propose that SEH toxin of S. aureus could be a useful candidate for therapeutic researches in cancer vaccine development.

Selective Host Cell Death by Staphylococcus aureus: A Strategy for Bacterial Persistence

Host cell death programs are fundamental processes that shape cellular homeostasis, embryonic development, and tissue regeneration. Death signaling and downstream host cell responses are not only critical to guide mammalian development, they often act as terminal responses to invading pathogens. Here, we briefly review and contrast how invading pathogens and specifically Staphylococcus aureus manipulate apoptotic, necroptotic, and pyroptotic cell death modes to establish infection. Rather than invading host cells, S. aureus subverts these cells to produce diffusible molecules that cause death of neighboring hematopoietic cells and thus shapes an immune environment conducive to persistence. The exploitation of cell death pathways by S. aureus is yet another virulence strategy that must be juxtaposed to mechanisms of immune evasion, autophagy escape, and tolerance to intracellular killing, and brings us closer to the true portrait of this pathogen for the design of effective therapeutics and intervention strategies.

Virulence factors and antimicrobial resistance in Staphylococcus aureus isolated from bovine mastitis in Brazil

This study aimed to evaluate virulence factors and genetic markers of antimicrobial resistance in 400 Staphylococcus aureus strains isolated from bovine mastitis in four Brazilian states, as well as to assess the association between these characteristics and field information. Virulence factors and drug resistance genes were identified by PCR screening. Biofilm-forming and hemolytic phenotype were detected using Congo red Tryptic Soy Broth and defibrinated sheep blood agar, respectively. Of all isolates, 83.5% were biofilm-forming and 98.5% strains exhibited biofilm gene icaAD, and a significant association between phenotype and genotype for biofilm was observed (P = 0.0005). Hemolysin genes were observed in 82.85% (hla⁺hlb⁺), 16.5% (hla⁺) and 0.75% (hlb⁺) isolates, whereas the hemolytic phenotype exhibited was complete and incomplete hemolysis in 64.25%, complete in 28.25%, incomplete in 4.75%, and negative in 2.75% of the strains. Virulence factors genes luk, seb, sec, sed, and tst were observed in 3.5%, 0.5%, 1%, 0.25%, and 0.74% isolates, respectively. The gene blaZ was detected in 82.03% of penicillin-resistant isolates, whereas tetK and aac(6')-Ie-aph(2')-Ia were observed in 33.87% and 45.15% of the tetracycline and aminoglycosides-resistant isolates, respectively. Fluoroquinolone resistance gene mepA was detected for the first time in S. aureus from bovine mastitis. Resistance genes tetM (3.22%), tetL (1.61%), ermA (14.29%), ermB (14.29%), ermC (33.3%), ermT (9.52%), ermY (4.76%), msrA (9.52%), and mphC (9.52%) were also detected among resistant isolates. No association between virulence factors or antimicrobial-resistant genes and year of isolation, geographic origin, or antimicrobial resistance profile was observed. Our results showed that S. aureus strains isolated from bovine mastitis in the four Brazilian states sampled are mainly biofilm-forming and hemolytic, whereas virulence genes associated with enterotoxins, luk and tst, were less frequently observed. Moreover, a wide variety of resistance genes that confer resistance to almost all classes of antimicrobial agents approved for use in animals and humans were found. Overall, the data point to a great pathogenic potential of S. aureus associated with bovine mastitis and to the non-negligible risks to public health of staphylococcal infections from animal origin.

Relationship between virulence factors and antimicrobial resistance in Staphylococcus aureus from bovine mastitis

OBJECTIVES

This review summarizes the literature on the role of virulence and antimicrobial resistance genes of Staphylococcus aureus in bovine mastitis, focusing on the association between these characteristics and their implications for public and animal health.

CONCLUSIONS

There is the possibility of antimicrobial resistance gene exchange among different bacteria, which is of serious concern in livestock husbandry, as well as in the treatment of human staphylococcal infections.

Matrine and baicalin inhibit apoptosis induced by Panton-Valentine leukocidin of Staphylococcus aureus in bovine mammary epithelial cells

It was previously thought that the Panton-Valentine leukocidin (PVL) toxin of Staphylococcus aureus (S. aureus) was not the main cause of cow mastitis. However, in recent years, detection of the gene encoding PVL has been increasing in dairy cow mastitis, which implies that PVL may be related to bovine mastitis. Therefore, we wanted to search for drugs inhibiting PVL or PVL-induced apoptosis. In this report, we investigated the apoptosis mechanism of PVL in bovine mammary epithelial cells (BMEC) and the inhibition mechanism of matrine and baicalin on PVL-induced apoptosis of BMEC. The results demonstrated that BMEC were damaged and underwent apoptosis by a standard PVL-producing strain of S. aureus (ATCC 49775), a PVL knockout mutant Δpvl 49775, complemented mutant C-Δpvl 49775, or recombinant (r)PVL in vitro. The rates of apoptosis and necrosis induced by S. aureus ATCC 49775 and C-Δpvl 49775 were significantly higher than those induced by Δpvl 49775, demonstrating that BMEC apoptosis and necrosis were associated with PVL. In addition, this research found matrine and baicalin could inhibit the apoptosis of BMEC induced by PVL-producing S. aureus and by rPVL. Matrine downregulated protein expression levels of endogenous and exogenous cleaved caspase-3, cleaved caspase-8, and cleaved caspase-9, and the effect was pronounced at a concentration of 50 μg/mL. Baicalin downregulated the expression of cleaved caspase-9. These results suggested that matrine and baicalin may have potential value against cow mastitis caused by the toxin PVL.

Molecular modelling and docking analysis of pleurocidin (an antimicrobial peptide) like peptides with enterotoxin H from Klebsilla pneumonia

Enterotoxin H is a key molecular target for replication and establishment of Klebsilla pneumonia in the host. Therefore, it is of interest to study the interaction of enterotoxin H with pleurocidin like peptides using molecular modelling (template PDB ID: 1YCE), Lig-Plot (ligand construction) and docking tools for therapeutic consideration. The hydrophobic pocket and the active site residues (Val 13, Met 16, Gly 25, Ala 25, and Ile 28) were identified using Cast P, Molegro and Sitehound tools. Docking results show that the pleurocidin like peptides interacts with the active sites of enterotoxin H with 300.96 docking score with optimal binding features.

Study of the effectiveness of staphylococcins in biopreservation of Minas fresh (Frescal) cheese with a reduced sodium content

Reducing salt content in foods such as cheeses, while limiting the growth of spoilage microorganisms and foodborne pathogens, is a difficult challenge. One method that may prove useful is use of staphylococcins, which are bacteriocins produced by staphylococci. Therefore, staphylococcin antimicrobial activity against six strains of S. aureus isolated from cheese was tested aiming at their industrial application in biopreservation of Minas fresh (Frescal) cheese with reduced sodium content. Three staphylococcins were selected for these tests: Pep 5, aureocin A53 and lysostaphin. All three staphylococcins proved to be bacteriolytic against all six strains of S. aureus. The antimicrobial activity of the partially purified staphylococcins was subsequently investigated against strains S. aureus Q1 and QJ3 in cheese matrices (6.0 log CFU/g) with different NaCl contents (control, a 25% reduction, and a 50% reduction), kept under refrigeration at 4 °C, for 21 days. Both strains were shown to be of concern for food industry as they carry the SEA, SEB and SEH enterotoxin genes, and are resistant to β-lactam drugs and moderate biofilm formers when grown in TSB. When used singly, Pep5, aureocin A53 and lysostaphin reduced approximately 95%, 99% and 99.99% of the viable cell counts, respectively, irrespective of the sodium content of the cheese matrix. The combined action of aureocin A53 and Pep5 resulted in an additional and significant reduction (p < 0.05) of ~1.0 log CFU/g when compared with the reduction caused by the use of either one singly. The combined action of lysostaphin and aureocin A53 or lysostaphin and Pep5 resulted in a reduction similar to or slightly smaller (p > 0.05) than that observed when lysostaphin was employed singly. Lysostaphin also proved to reduce the number of the staphylococcal viable cells to a level (~ 2.0 log CFU/g) at which enterotoxin production should not reach a sufficient quantity to cause food poisoning. Therefore, lysostaphin may have a practical application in the food industry to control staphylococcal contamination of Minas fresh cheese with a sodium content reduced up to 50%, providing consumers with more safe options to reduce their intake of sodium.

NDRG1 negatively regulates proliferation and Milk bio-synthesis of bovine epithelial cells via the mTOR signaling pathway

The expression of N-myc downstream-regulated gene 1 (NDRG1) was significantly correlated with diverse processes such as cell growth and differentiation, lipid synthesis, stress and immune responses. Here we explored the role of NDRG1 expression in bovine mammary tissue and epithelial cells under an inflammatory condition. Results showed that NDRG1 expression was elevated in bovine mammary tissue with mastitis and mammary epithelial cells treated by heat inactivated Escherichia coli and Staphylococcus aureus compared to normal tissue and untreated cells. Overexpression of NDRG1 significantly inhibited cell proliferation and migration, β-casein secretion, gene expressions of inflammatory cytokines tumor necrosis factor-α, interleukin (IL)-6 and IL-8, and activation of mTOR signal pathway of mammary epithelial cells, and vice versa by NDRG1 knockdown. These findings suggest that NDRG1 has immense potential in the regulation of properties in bovine mammary epithelial cells under an inflammatory condition.

Staphylococcal Enterotoxin C Is an Important Virulence Factor for Mastitis

Staphylococcus aureus is an important bacterial pathogen causing bovine mastitis, but little is known about the virulence factor and the inflammatory responses in the mammary infection. Staphylococcal enterotoxin C (SEC) is the most frequent toxin produced by S. aureus, isolated from bovine mastitis. To investigate the pathogenic activity of SEC in the inflammation of the mammary gland and the immune responses in an animal model, mouse mammary glands were injected with SEC, and the clinical signs, inflammatory cell infiltration, and proinflammatory cytokine production in the mammary glands were assessed. SEC induced significant inflammatory reactions in the mammary gland, in a dose-dependent manner. SEC-injected mammary glands showed a severe inflammation with inflammatory cell infiltration and tissue damage. In addition, interleukin (IL)-1β and IL-6 production in the SEC-injected mammary glands were significantly higher than those in the PBS control glands. Furthermore, the SEC-induced inflammation and tissue damage in the mammary gland were specifically inhibited by anti-SEC antibody. These results indicated, for the first time, that SEC can directly cause inflammation, proinflammatory cytokine production, and tissue damage in mammary glands, suggesting that SEC might play an important role in the development of mastitis associated with S. aureus infection. This finding offers an opportunity to develop novel treatment strategies for reduction of mammary tissue damage in mastitis.

Immunochemical assay with monoclonal antibodies for detection of staphylococcal enterotoxin H

Staphylococcal enterotoxins cause food poisoning of various degrees of severity. For milk and meat products, there is a high probability of contamination with staphylococcal enterotoxin H (SEH). In this regard specific and sensitive methods are required to be developed for its detection and monitoring. In this work, the gene seh was expressed and a preparation of recombinant toxin was obtained. Using hybridoma technology, a panel of high-affinity monoclonal antibodies (mAbs) to SEH was produced. The antibodies were characterized and shown to have no cross-reactivity towards the main staphylococcal enterotoxins (A, B, C1, D, E, G and I). Based on these mAbs, a method for specific and quantitative detection of SEH was developed in the format of sandwich enzyme immunoassay (linear range, 0.2–3 ng/ml). All the mAbs produced revealed SEH by immunoblotting. Immunochemical analysis of the culture fluids of staphylococcal isolates obtained from the milk of mastitis-infected cows by immunoblotting and sandwich enzyme immunoassay demonstrated the conformity of these methods. Using the developed method, the toxin was revealed in blood serum and liquid food products practically to 100%. From non-liquid foods, it was shown to be extracted to a maximum with a buffer of pH 4.0–4.5.

Exotoxin diversity of Staphylococcus aureus isolated from milk of cows with subclinical mastitis in Central Russia

Mastitis, a major veterinary problem widespread in many regions, is caused mainly by Staphylococcus spp. However, there is no current reliable information about the role of Staphylococcus aureus and their toxins in the development of mastitis in cows in the territory of the Russian Federation. The aim of this investigation was to determine the profile of exotoxins of S. aureus from cow milk from farms of Central Russia. A total of 60 isolates of S. aureus were obtained from milk samples of cows with the subclinical form of mastitis. The exotoxin genes were identified using 2 types of PCR assays. The diversity of enterotoxin genes was studied by multiplex PCR. The percentage occurrence of enterotoxin genes was as follows: sea, 53.3%; seb, 3.3%; sec, 50%; sed, 4%; see, 46.6%; seg, 70%; sei, 10%; selp, 3.3%; and tsst1, 1.6%. The seh gene was not detected. The genes of pore-forming toxins and phenol-soluble modulins were identified by singleplex PCR and consisted of the following: hlA, 70%; lucS, 46.6%; psmA, 81.6%; psmB, 95%; and hld, 78.3%. The most abundant genes were psm (psmB, 95%), which codes for pore-forming toxins, and seg (70%), which codes for enterotoxins. The production of some enterotoxins in bacterial culture medium was detected by ELISA. The level of toxin production was near 1 ng/mL for SEA, SEE, SEG, SEI, SELP, and TSST-1 and reached a maximal level of 18 ng/mL for SEE. In the present work, we show that subclinical mastitis in cows is associated with S. aureus in the central region of the Russian Federation. Most of the isolates containing enterotoxin genes also had cytotoxin genes.

Prototheca zopfii Induced Ultrastructural Features Associated with Apoptosis in Bovine Mammary Epithelial Cells

Prototheca zopfii infections are becoming global concerns in humans and animals. Bovine protothecal mastitis is characterized by deteriorating milk quality and quantity, thus imparting huge economic losses to dairy industry. Previous published studies mostly focused on the prevalence and characterization of P. zopfii from mastitis. However, the ultrastructural pathomorphological changes associated with apoptosis in bovine mammary epithelial cells (bMECs) are not studied yet. Therefore, in this study we aimed to evaluate the in vitro comparative apoptotic potential of P. zopfii genotype-I and -II on bMECs using flow cytometry, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed fast growth rate and higher adhesion capability of genotype-II in bMECs as compared with genotype-I. The viability of bMECs infected with P. zopfii genotype-II was significantly decreased after 12 h (p < 0.05) and 24 h (p < 0.01) in comparison with control cells. Contrary, genotype-I couldn't show any significant effects on cell viability. Moreover, after infection of bMECs with genotype-II, the apoptosis increased significantly at 12 h (p < 0.05) and 24 h (p < 0.01) as compared with control group. Genotype-I couldn't display any significant effects on cell apoptosis. The host specificity of P. zopfii was also tested in mouse osteoblast cells, and the results suggest that genotype-I and -II could not cause any significant apoptosis in these cell lines. SEM interpreted the pathomorphological alterations in bMECs after infection. Adhesion of P. zopfii with cells and further disruption of cytomembrane validated the apoptosis caused by genotype-II under SEM. While genotype-1 couldn't cause any significant apoptosis in bMECs. Furthermore, genotype-II induced apoptotic manifested specific ultrastructure features, like cytoplasmic cavitation, swollen mitochondria, pyknosis, cytomembrane disruption, and appearance of apoptotic bodies under TEM. The findings of the current study revealed that genotype-II has the capability to invade and survive within the bMECs, thus imparting significant damages to the mammary cells which result in apoptosis. This study represents the first insights into the pathomorphological and ultrastructure features of apoptosis in bMECs induced by P. zopfii genotype-II.

Frequência de genes codificadores de toxinas em Staphylococcus aureus isolados de leite de tanques expansão comunitários

RESUMO: A capacidade de produção de toxinas pelo Staphylococcus aureus no leite e produtos derivados está relacionado com surtos de intoxicação alimentar. Objetivou-se nesta pesquisa, estudar a ocorrência de genes que codificam para enterotoxinas estafilocócicas (sea, seb, sed, seg, seh e sei) e toxinas α e β hemolítica (hla e hlb) em S. aureus isolados de 53 amostras de leite de tanques expansão comunitários no Estado de Alagoas, Brasil. Foram identificados 27 isolados (50,94%) como S. aureus pela amplificação do gene nuc. 13/27 isolados (48,1%) foram positivos para pelo menos um gene das enterotoxinas estudadas, sendo as frequências dos genes sea 33,3%, seh 18,5%, sei 11,1% e sed 7,4%; não entanto não foram identificados os genes seb e seg nestas bactérias. Para as toxinas hemolíticas, 51,9% dos isolados portavam ambos genes (hla e hlb), sendo a frequência para o gene hla de 81,5% e para o gene hlb de 51,9%. A frequência de genes das toxinas avaliadas é alta o que constitui um risco potencial para a saúde pública em especial, as enterotoxinas por serem termoestáveis e estarem asssociados com surtos de intoxicação alimentar.

Identification and measurement of staphylococcal enterotoxin M from Staphylococcus aureus isolate associated with staphylococcal food poisoning

Staphylococcus aureus produces a wide variety of staphylococcal enterotoxins (SEs, SEA to SEX), which are responsible for staphylococcal food poisoning. This study is aimed to establish a system to detect staphylococcal enterotoxin M (SEM) protein in food matrixes. In the present study, sem gene was characterized in a S. aureus isolate H4 associated with food poisoning. The amino acid sequence of the deduced SEM protein was same as that of previously identified SEM from S. aureus 04-02981. Subsequently, mature SEM protein was expressed in Escherichia coli BL21 (DE3) cells and purified with a Ni-NTA spin column. The polyclonal and monoclonal antibody against it were prepared. Using these antibodies, a highly sensitive, specific sandwich enzyme-linked immunosorbent assay (ELISA) system was developed capable of detecting SEM in milk, meat and rice. Cross-reactivity with SEB, SEI and SEK in this method was insignificant. Quantification of SEM secretion in vitro using this novel capture ELISA revealed that SEM was mainly secreted during the transition from the exponential to the stationary phase. Furthermore, sem gene and SEM protein production were screened by PCR and the developed ELISA system. The results indicated that there were two SEM+ strains of 19 S. aureus isolates originating in cold dishes and humans suffering from food poisoning. The investigations make it possible to assess SEM in food hygiene supervision in near future.

SIGNIFICANCE AND IMPACT OF THE STUDY

Staphylococcal enterotoxins (SE) are the main causative agents of staphylococcal food poisoning. Unlike classical SEs (SEA to SEE), the relationship between newly identified SEs (SEG to SEX) and staphylococcal food poisoning has not been clearly elucidated. Recently, mild emetic potential of staphylococcal enterotoxin M (SEM) has been demonstrated, which indicated that SEM might be associated with food poisoning. However, there is currently no commercial enzyme-linked immunosorbent assay (ELISA) kit available for immunological detection of it. Therefore, we developed a highly sensitive, specific sandwich ELISA system and assayed SEM in food matrixes. This assay facilitates the study of SEM expression in vitro and in vivo. In addition, the investigations would be helpful in addressing the relative incidence of SEM+ strains in near future.

Molecular characterization and antibiotic resistance of Staphylococcus spp. isolated from cheese processing plants

The aim of this research paper was to characterize coagulase-positive and coagulase-negative staphylococci from raw milk, Minas cheese, and production lines of Minas cheese processing. One hundred isolates from 3 different cheese producers were characterized using molecular approaches, such as PCR, molecular typing, and DNA sequencing. Staphylococcus aureus (88% of the isolates) was the most abundant followed by Staphylococcus epidermidis, Staphylococcus hyicus, and Staphylococcus warneri. Among the 22 enterotoxin genes tested, the most frequent was seh (62% of the isolates), followed by selx and ser. Hemolysin genes were widely distributed across isolates, and Panton-Valentine leukocidin and toxic shock syndrome toxin genes were also identified. Methicillin-resistant S. aureus were staphylococcal cassette chromosome mec III, IVa, IVd, and others nontypeable. In the phenotypic antibiotic resistance, multiresistant isolates were detected and resistance to penicillin was the most observed. Using spa typing, we identified several types and described a new one, t14969, isolated from cheese. These findings suggest that antibiotic resistance and potentially virulent strains from different sources can be found in the Brazilian dairy processing environment. Further research should be conducted with collaboration from regulatory agencies to develop programs of prevention of virulent and resistant strain dissemination in dairy products and the processing environment.