Enterotoxins A and B produced by Staphylococcus aureus increase cell proliferation, invasion and cytarabine resistance in acute myeloid leukemia cell lines

As in the case of cancer, the risk of infection increases when the host's immune system is not working properly. It has been shown that toxins produced by the bacteria responsible for bacterial infections can alter the properties of cancer cells as well as their sensitivity to chemotherapy agents. Staphylococcus aureus (S. aureus) is one of the most prevalent pathogens in acute myeloid leukemia (AML) patients and it produces several virulence factors, including Staphylococcal enterotoxin A (SEA) and Staphylococcal enterotoxin B (SEB). Cytotoxicity, transwell migration, invasion assays, and various transcriptomic and gene set enrichment (GSE) analyses were used to determine how SEA and SEB alter cell proliferation, migration, invasion, and Cytarabine (Cyt) resistance in AML cell lines. The treatment of AML cell lines with SEA/SEB caused an increase in cell proliferation and Cyt resistance. Toxins enhanced the proclivity of cells to migrate and invade, with around 50% of cells in the presence of SEA and SEB. Transcriptomic and gene set enrichment analyses, and subsequent PCR validations showed dysregulation of immune related genes and genesets. Apparently, this allows AML cells to escape and survive the undesirable environment created by toxins, possibly via the ER stress signaling pathway. Therefore, SEA and SEB can significantly alter the characteristics of AML cancer cells and evaluation of alterations in responsible immune genes and pathways may be crucial for controlling the progression of cancer. In addition, our results suggest that there may be a strong interaction between the immune related pathways and the ER signaling pathway.

Optimization and evaluation of a multiplex PCR assay for detection of Staphylococcus aureus and its major virulence genes for assessing food safety

Staphylococcus aureus is a natural commensal microflora of humans which causes opportunistic infections due to its large arsenal of exotoxins, invasion, immune evasion, and antibiotic resistance mechanisms. The primary goal of this study is to develop a multiplex PCR (mPCR) assay for simultaneous detection of Staphylococcus aureus (nuc) and its virulence genes coding for prominent exotoxins namely alpha hemolysin (hla), enterotoxins A (sea), enterotoxin B (seb), toxic shock syndrome toxin (tsst-1), and the gene coding for methicillin resistance (mecA). A competitive internal amplification control (IAC) was included in the assay to exclude the false negative outcomes. Highly specific primer pairs were designed for the target genes using in silico resources. At the outset, monoplex PCRs were standardized using reference S. aureus strains. Primer specificity to the target genes was authenticated through restriction digestion analysis of amplified PCR products. Multiplex PCR was optimized in increments of one gene starting with nuc and IAC amplified simultaneously using one pair of primers (nuc) in a competitive manner. The mPCR assay was found to be highly sensitive with a detection limit of ~10 CFUs per reaction for pure cultures. Multiplex PCR assay was further evaluated on the retail and processed food samples to test the prevalence of S. aureus and study their exotoxin profiles. Of the 57 samples examined, 13 samples (22.80%) were found to be contaminated with S. aureus whose DNA was extracted after a 6-h enrichment period. Among these, a high percentage of hemolytic and enterotoxin A positive strains were encountered. The mPCR assay developed in this study would be a useful tool for rapid and reliable monitoring of S. aureus for food quality testing and from clinical infections.

Kinetics of Staphylococcus aureus growth and Enterotoxin A production in milk under shaking and static conditions

Numerous studies on bacterial growth or survival predictive models have been conducted since the establishment of predictive microbiology. However, limited research focused on the prediction of bacteria-producing enterotoxins, which are often the causative agents of food-borne diseases. This study aimed to determine an appropriate kinetic model of staphylococcal enterotoxin A (SEA) production in milk after contamination with Staphylococcus aureus. An S. aureus strain producing SEA was inoculated into milk with an initial inoculum concentration of approximately 3.0 log CFU/mL. All samples were incubated for 30-48 h at 20 °C ± 1 °C, 28 °C ± 1 °C, and 36 °C ± 1 °C separately under shaking or static conditions. Duplicate samples were carried out at appropriate intervals to count the number of S. aureus colonies and detect the concentration of SEA. Experimental results showed that the SEA concentration curves under all experimental conditions were sigmoidal and consisted of three phases: lag, exponential, and stationary. Thus, the modified Gompertz model was used to describe the profile of SEA concentration in milk during the incubation. A good fitting accuracy (R² > 0.97) indicated that the modified Gompertz model was appropriate. In addition to temperature, shaking during incubation also affected the maximal production rate of SEA and the maximal SEA concentrations, and shortened the lag phase at lower incubation temperatures, suggesting that the mechanical movements (e.g., stirring, pumping, and flowing) during the milk processing would increase the risk of SEA occurrence. Besides, the time to detection (TTD) of SEA was found to range from 3 to 24.5 h at temperatures of 36 °C ± 1 °C-20 °C ± 1 °C, at which time the concentrations of S. aureus ranging from 5.0 log CFU/mL-6.9 log CFU/mL at the TTD. This study contributed to understanding the kinetics of SEA production and the possible factors affecting the synthesis of SEA during the manufacturing of liquid foods, such as milk.

Maternal immune activation with staphylococcal enterotoxin A produces unique behavioral changes in C57BL/6 mouse offspring

Stimulation of the immune system during pregnancy, known as maternal immune activation (MIA), can cause long-lasting neurobiological and behavioral changes in the offspring. This phenomenon has been implicated in the etiology of developmental psychiatric disorders, such as autism and schizophrenia. Much of this evidence is predicated on animal models using bacterial agents such as LPS and/or viral mimics such as Poly I:C, both of which act through toll-like receptors. However, fewer studies have examined the role of direct activation of maternal T-cells during pregnancy using microbial agents. Bacterial superantigens, such as Staphylococcal Enterotoxin A and B (SEA; SEB), are microbial proteins that activate CD4+ T-cells and cause prominent T-cell proliferation and cytokine production. We injected pregnant and non-pregnant adult female C57BL/6 mice with 200 μg/Kg of SEA, SEB, or 0.9% saline, and measured splenic T-cell-derived cytokine concentrations (viz., IL-2, IFN-γ, IL-6, and IL-4) 2 h later; animals injected with SEA were also measured for splenic concentrations of TNF-α and IL-17A. Half of the injected pregnant animals were brought to term, and their offspring were tested on a series of behavioral tasks starting at six weeks of age (postnatal day 42 [P42]). These tasks included social interaction, the elevated plus maze (EPM), an open field and object recognition (OR) task, prepulse inhibition (PPI) of sensorimotor gating, and the Morris water maze (MWM). Results showed that SEA and SEB induced significant concentrations of all measured cytokines, and in particular IFN-γ, although cytokine responses were greater following SEA exposure. In addition, pregnancy induced an inhibitory effect on cytokine production. Behavioral results showed distinct phenotypes among offspring from SEA- or SEB-injected mothers, very likely due to differences in the magnitude of cytokines generated in response to each toxin. Offspring from SEA-injected mothers displayed modest decreases in social behavior, but increased anxiety, locomotion, interest in a novel object, and short-term spatial memory, while offspring of SEB-injected mothers only exhibited increased anxiety and locomotion. There were no deficits in PPI, which was actually pronounced in SEA and SEB offspring. Overall, the novel use of SEA and SEB as prenatal immune challenges elicited distinct behavioral profiles in the offspring that both mirrors and diverges from previous models of maternal immune activation in important ways. We conclude that superantigen-induced T-cell-mediated maternal immune activation is a valid and valuable model for studying and expanding our understanding of the effects of prenatal immune challenge on neurodevelopmental and behavioral alterations in offspring.

Staggered Target SELEX, a novel approach to isolate non-cross-reactive aptamer for detection of SEA by apta-qPCR

BACKGROUND AND OBJECTIVE

Aptamers or chemical antibodies are oligonucleotides (DNA or RNA) that are able to bind to various targets with high specificity and affinity such as toxins which are isolated by an in vitro method known as SELEX. To date, there are many SELEX procedures for the isolation of novel aptamers against proteins. However not all modified SELEX are suitable for similar protein based on sequence homology such as staphylococcal enterotoxins. Staphylococcal enterotoxin type A (SEA) is the most prevalent toxin involved in staphylococcal food poisoning (SFP) worldwide. SEA is homologous to Staphylococcal enterotoxin type D (SED) and Staphylococcal enterotoxin type E (SEE) about 50% and 83%, respectively. Here, we have developed Staggered Target SELEX (ST-SELEX) as a novel designed SELEX procedure to acquire specific non-cross-reactive aptamers against SEA as a model protein.

METHODS

In this study, isolated ssDNA aptamers by ST-SELEX were used for detection of SEA via apta-Real time PCR (apta-qPCR). After in silico analysis of SEA protein with SEE and finding the specific region on the surface of protein, ST-SELEX was carried out in two steps (classical SELEX and Second SELEX). Finally, after isolating high specific aptamers, the apta-qPCR was used for the detection of the SEA. In this technique, poly-clonal antibody against SEA was immobilized on protein G sepharose beads (Ab-PGs). Then, the SEA protein was captured by poly clonal antibody as the target that immobilized on sepharose beads. The isolated aptamers were bound on the surface of SEA protein that captured by Ab-PGs. Finally, the heat-released aptamers were amplified by qPCR.

RESULT

Our investigation showed that the aptamers were generated in vitro by a ten-round selection process based on ST-SELEX procedure with dissociation constant (K_D) value 7.44± 0.6 nM and limit of detection (LOD) of 146.67 fM.

DISCUSSION AND CONCLUSION

The advantage of ST-SELEX compared to other SELEX methods was to select a specific non cross-reactive aptamer against two or more proteins with high sequence homology. These aptamers can be used in sensitive detection methods such as apta-qPCR.

Manufacturing of a novel double-function ssDNA aptamer for sensitive diagnosis and efficient neutralization of SEA

Staphylococcal enterotoxin A (SEA) is an enterotoxin produced mainly by Staphylococcus aureus. In recent years, it has become the most prevalent compound for staphylococcal food poisoning (SFP) around the world. In this study, we isolate new dual-function single-stranded DNA (ssDNA) aptamers by using some new methods, such as the Taguchi method, by focusing on the detection and neutralization of SEA enterotoxin in food and clinical samples. For the asymmetric polymerase chain reaction (PCR) optimization of each round of systematic evolution of ligands by exponential enrichment (SELEX), we use Taguchi L9 orthogonal arrays, and the aptamer mobility shift assay (AMSA) is used for initial evaluation of the protein-DNA interactions on the last SELEX round. In our investigation the dissociation constant (K_D) value and the limit of detection (LOD) of the candidate aptamer were found to be 8.5 ± 0.91 of nM and 5 ng/ml using surface plasmon resonance (SPR). In the current study, the Taguchi and mobility shift assay methods were innovatively harnessed to improve the selection process and evaluate the protein-aptamer interactions. To the best of our knowledge, this is the first report on employing these two methods in aptamer technology especially against bacterial toxin.

Biosynthesis of staphylococcal enterotoxin A by genetic engineering technology and determination of staphylococcal enterotoxin A in water by HPLC-ESI-TOF

Staphylococcal enterotoxin A (SEA) was the major virulence factor of Staphylococcus aureus and a biomarker of S. aureus. To establish a fast, low cost, high accuracy, reliable, and simple method for detecting S. aureus, SEA was analyzed by HPLC-ESI-TOF. SEA was not yet commercially available in universal, so SEA was prepared before it was analyzed by HPLC-ESI-TOF. The result showed that high purified SEA was successfully prepared and SEA has normal distribution in mass spectra. A large amount of recombinant SEA (rSEA) was obtained by engineering technology and was purified by Ni affinity chromatography column, and the expression and purity of rSEA and SEA were analyzed by SDS-PAGE. The factors effected on ionization of SEA were studied, and the qualitative analysis of SEA by HPLC-ESI-TOF. The result showed that large amount of SEs expressed within a short time at 28 °C or thereabouts, and there was no impurity bands in electrophorogram after rSEA was purified by Ni affinity chromatography column. In addition, the SEA which had homologous AA sequence with wild SEA was made by rSEA. The retention of SEA in column and ionization of SEA in ESI-TOF were studied for qualitative analysis of S. aureus. The result showed that the content of formic acid in mobile phase was an important factor for ionization of SEs in ESI-TOF. And the result provided theoretical foundation for qualitative detection of S. aureus. [SEs + nH⁺ + mNH₄⁺] ^n+m+ was shown on ESI-TOF spectra when SEA was detected by ESI-TOF in positive ion mode, and the numerical value of n+m was less than or equal to the number of basic amino acids in SEs. This method was applied to determine SEA in water samples preliminarily, and the detection limit of SEA in spiked water sample was 3 mg/kg. The limit of detection of 3 mg/kg was low sensitivity for low molecular weight matters, but it was high sensitivity for SEA which had a high molecular weight of 27 kDa. Of SEA, 3 mg/kg was equivalent to 10^-4 mmol/kg of SEA. This study can provide evidence for establishing method to determine SEA in real samples.

Survival of Staphylococcus aureus in dried fish products as a function of temperature

We evaluated the survival ability of Staphylococcus aureus and the production of Staphylococcal enterotoxin A (SEA) in dried filefishes and julienned squid at 10°, 24°, and 35 °C for 5 months. S. aureus survived longer at 10 °C than 24° and 35 °C, and better in dried julienned squid than dried filefishes. At 35 °C, the populations of S. aureus were rapidly diminished and undetectable in dried filefishes and julienned squid after 14 and 19 days, respectively. SEA production did not increase during the 5-month storage period, regardless of the temperature and type of dried fish products. Although it is advised to store dried fish products at 10 °C for quality control in retail markets, refrigerated temperature is more likely to facilitate the survival of S. aureus in dried fish products. Thus, dried fish products should be produced and stored under hygienic conditions.

Increased numbers and suppressive activity of regulatory CD25(+)CD4(+) T lymphocytes in the absence of CD4 engagement by MHC class II molecules

Mechanisms of central and peripheral tolerance prevent autoimmunity. Regulatory T cells inhibit the activation of potentially auto-reactive T cells in peripheral lymphoid organs. In transgenic mice in which all MHC class II molecules are incapable of binding to CD4, class II MHC-restricted T cells preferentially differentiated into immunosuppressive, regulatory T cells. In these mutant MHC class II transgenic mice, a subset of CD4(+) T cells constitutively expressed moderately elevated levels of CD25 and potently inhibited interleukin-2 secretion by T cells from normal mice in a cell-to-cell, contact-dependent manner. Immunosuppressive activity depended on activation of the regulatory T cells. Thus, CD25(+)CD4(+) T cells from mutant MHC class II transgenic mice resembled phenotypically and functionally a major subset of natural regulatory T cells in normal mice, but were two to three-times more abundant. These results further clarify the mechanisms that govern the differentiation and maintenance of CD25(+)CD4(+) regulatory T cells, and present avenues for immunomodulation.

Potential Immunoinflammatory Role of Staphylococcal Enterotoxin A in Atopic Dermatitis: Immunohistopathological Analysis and in vitro Assay

Background

The underlying mechanism of atopic dermatitis (AD) exacerbated by Staphylococcus aureus has not been established. However, we demonstrated recently that the majority of S. aureus strains colonized in the skin of Korean AD patients carried genes encoding staphylococcal enterotoxin A (SEA) and/or toxic shock syndrome toxin-1 (TSST-1).

Objective

To clarify the role of staphylococcal superantigen, SEA in AD.

Methods

With the lesional skin of 9 AD patients and normal looking skin of one healthy adult, we examined first the expression of SEA, staphylococcal enterotoxin B (SEB), and TSST-1 using immunohistochemical analysis. In addition, we investigated the effects of SEA on the expression of inflammation-related adhesion molecules and cytokines in human HaCaT keratinocytes and Human Umbilical Vein Endothelial Cells (HUVECs) by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis and enzyme-linked immunosorbent assay.

Results

Staphylococcal protein A (SPA) and SEA were detected with increased immunoreactivity in AD patients. However, TSST-1 showed mild-to-moderate immunoreactivity in AD patients, whereas SEB was minimally detected. In the double immunofluorescence investigation, SEA and SPA were well co-localized. SEA induced upregulation of adhesion molecules and elicited inflammatory responses in HaCaT keratinocytes and HUVECs.

Conclusion

This study demonstrates the importance of SEA as an immunoinflammatory triggering factor of AD in Koreans.

Interaction of staphylococcal toxic shock syndrome toxin-1 and enterotoxin A on T cell proliferation and TNFα secretion in human blood mononuclear cells

BACKGROUND

The majority of menstrual toxic shock syndrome (MTSS) cases are caused by a single clone of Staphylococcus aureus that produces both toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin A (SEA).

OBJECTIVE

To determine whether the two superantigens interact to cause an enhancement of biological activity in human peripheral blood mononuclear cells (PBMCs).

DESIGN

PBMCs from nine healthy donors were stimulated with TSST-1 or SEA, either alone or in combination at their minimum effective concentrations.

SETTING

In vitro study.

INTERVENTIONS

Human PBMCs were stimulated in vitro with TSST-1 (1 pg/mL), SEA (0.1 pg/mL) or combination for 20 to 72 h. Mitogenic response was determined by [(3)H]-thymidine incorporation. PBMC culture supernatants were assayed for the presence of tumour necrosis factor-alpha (TNFα), interleukin (IL)-1β and IL-6 by ELISA.

MAIN RESULTS

The combination of TSST-1 and SEA induced significantly greater mitogenesis in human PBMCs compared with either toxin alone (P<0.05, paired Student's t test, two-tailed). Similarly, the production of TNFα in culture supernatants was significantly greater in the combination of TSST-1 and SEA compared with either TSST-1 or SEA alone (P<0.05). In contrast, no enhancement in the levels IL-1 or IL-6 was observed.

CONCLUSIONS

These data suggest that the co-production of TSST-1 and SEA by S aureus may provide some biological advantage to the organism throughs an enhanced effect of these superantigens on T cell activation and TNF secretion.