High production of egc2-related staphylococcal enterotoxins caused a food poisoning outbreak

Discovery of potential anti- Staphylococcus aureus natural products and their mechanistic studies using machine learning and molecular dynamic simulations

The structure-activity analysis (SAR) and machine learning were used to investigate potential anti-S. aureus agents in a faster method. In this study, 24 oxygenated benzene ring components with S. aureus inhibition capacity were confirmed by literature exploring and in-house experiments, and the SAR analysis suggested that the hydroxyl group position may affect the anti-S. aureus activity. The 2D-MLR-QSAR model with 9 descriptors was further evaluated as the best model among the 21 models. After that, hesperetic acid and 2-HTPA were further explored and evaluated as the potential anti-S. aureus agents screening in the natural product clustering library through the best QSAR model calculation. The antibacterial capacities of hesperetic acid and 2-HTPA had been investigated and proved the similar predictive pMIC value resulting from the QSAR model. Besides, the two novel components were able to inhibit the growth of S. aureus by disrupting the cell membrane through the molecular dynamics simulation (MD), which further evidenced by scanning electron microscopy (SEM) test and PI dye results. Overall, these results are highly suggested that QSAR can be used to predict the antibacterial agents targeting S. aureus, which provides a new paradigm to research the molecular structure-antibacterial capacity relationship.

Carbon nanotubes: a novel innovation as food supplements and biosensing for food safety

Recently, nanotechnology has emerged as an extensively growing field. Several important fabricated products including Carbon nanotubes (CNTs) are of great importance and hold significance in several industrial sectors, mainly food industry. Recent developments have come up with methodologies for the prevention of health complications like lack of adequate nutrition in our diet. This review delves deeper into the details of the food supplementation techniques and how CNTs function in this regard. This review includes the challenges in using CNTs for food applications and their future prospects in the industry. Food shortage has become a global issue and limiting food resources put an additional burden on the farmers for growing crops. Apart from quantity, quality should also be taken into consideration and new ways should be developed for increasing nutritional value of food items. Food supplementation has several complications due to the biologically active compounds and reaction in the in vivo environment, CNTs can play a crucial role in countering this problem through the supplementation of food by various processes including; nanoencapsulation and nanobiofortification thus stimulating crop growth and seed germination rates. CNTs also hold a key position in biosensing and diagnostic application for either the quality control of the food supplements or the detection of contagions like toxins, chemicals, dyes, pesticides, pathogens, additives, and preservatives. Detection such pathogens can help in attaining global food security goal and better production and provision of food resources. The data used in the current review was collected up to date as of March 31, 2024 and contains the best of our knowledge. Data collection was performed from various reliable and authentic literatures comprising PubMed database, Springer Link, Scopus, Wiley Online, Web of Science, ScienceDirect, and Google Scholar. Research related to commercially available CNTs has been added for the readers seeking additional information on the use of CNTs in various economic sectors.

Isolation and genetic characterization of Staphylococcus aureus from wild animal feces and game meats

The populations of Japanese deer and boar have increased dramatically and have a serious impact on farming and mountain villages. Although the Japanese government promotes the use of captured wild animals, game meat is not subject to sanitary control considering that it is not subject to meat inspection or quality control. Here, we have attempted to isolate Staphylococcus aureus, a typical foodborne pathogen, as a part of an investigation of contamination in the meats of wild animals and their processing stages. We examined 390 samples of deer feces, 117 samples of wild boar feces, and 75 samples of disemboweled deer meat for isolation of S. aureus; ultimately, 30 (positive rate: 7.7%), 2 (1.7%), and 21 (28.0%) strains were isolated, respectively, from the samples. The genome sequences of these isolates were analyzed and were subjected to multilocus sequence typing. We identified 12 new sequence types (STs) and a dominant population of S. aureus with a characteristic genetic background in wild animals, namely, the ST groups derived from CC121 (number of strains = 39). These strains did not harbor the enterotoxin gene or only harbored egc-related enterotoxin, which is of low involvement in Staphylococcal food poisoning. However, one ST2449 strain, which produces causative enterotoxins, was isolated from a deer's feces. Since there are several common STs isolated from feces and dismembered meat and because fecal contamination during dismemberment is suspected, continuous monitoring and guidance for improving sanitary management conditions during processing and handling of the meat are highly warranted with immediate effect.

Molecular Characteristics and Pathogenicity of Staphylococcus aureus Exotoxins

Staphylococcus aureus stands as one of the most pervasive pathogens given its morbidity and mortality worldwide due to its roles as an infectious agent that causes a wide variety of diseases ranging from moderately severe skin infections to fatal pneumonia and sepsis. S. aureus produces a variety of exotoxins that serve as important virulence factors in S. aureus-related infectious diseases and food poisoning in both humans and animals. For example, staphylococcal enterotoxins (SEs) produced by S. aureus induce staphylococcal foodborne poisoning; toxic shock syndrome toxin-1 (TSST-1), as a typical superantigen, induces toxic shock syndrome; hemolysins induce cell damage in erythrocytes and leukocytes; and exfoliative toxin induces staphylococcal skin scalded syndrome. Recently, Panton-Valentine leucocidin, a cytotoxin produced by community-associated methicillin-resistant S. aureus (CA-MRSA), has been reported, and new types of SEs and staphylococcal enterotoxin-like toxins (SEls) were discovered and reported successively. This review addresses the progress of and novel insights into the molecular structure, biological activities, and pathogenicity of both the classic and the newly identified exotoxins produced by S. aureus.

The Enterotoxin Gene Profiles and Enterotoxin Production of Staphylococcus aureus Strains Isolated from Artisanal Cheeses in Belgium

A Staphyloccoccus aureus is one of the leading causes of food poisoning outbreaks (FPOs) worldwide. Staphylococcal food poisoning (SFP) is induced by the ingestion of food containing sufficient levels of staphylococcal enterotoxins (SEs). Currently, 33 SEs and SE-like toxins (SEls) have been described in the literature, but only five named "classical" enterotoxins are commonly investigated in FPOs due to lack of specific routine analytical techniques. The aims of this study were to (i) establish the genetic profile of strains in a variety of artisanal cheeses (n = 30) in Belgium, (ii) analyze the expression of the SE(l)s by these strains and (iii) compare the output derived from the different analytical tools. Forty-nine isolates of S. aureus were isolated from ten Belgian artisanal cheeses and were analyzed via microbiological, immunological, liquid chromatography mass spectrometry, molecular typing and genetic methods. The results indicated that classical SEs were not the dominant SEs in the Belgian artisanal cheeses that were analyzed in this study, and that all S. aureus isolates harbored at least one gene encoding a new SE(l). Among the new SE(l)s genes found, some of them code for enterotoxins with demonstrated emetic activity and ecg-enterotoxins. It is worth noting that the involvement of some of these new SEs has been demonstrated in SFP outbreaks. Thus, this study highlighted the importance of the development of specific techniques for the proper investigation of SFP outbreaks.

Epidemiological and molecular evidence of foodborne poisoning outbreak caused by enterotoxin gene cluster-harboring Staphylococcus aureus of new sequence type 7591

OBJECTIVES

This paper presented a detailed analysis of the epidemiology and molecular characteristics of staphylococcal food poisoning (SFP) that occurred in a hotel in Hangzhou.

METHODS

A total of 46 guests at the hotel underwent an epidemiological survey. Samples of stool from patients, vomit, swabs from the kitchen, leftover food items, and anal swabs from food handlers were taken and investigated for the presence of potential pathogenic bacteria. Molecular techniques and whole genome sequencing were performed to track the evolution of Staphylococcus aureus associated with the outbreak of SFP.

RESULTS

Forty-six individuals displayed gastrointestinal symptoms. Seventeen isolates of S. aureus were discovered to carry the seg, sei, sem, sen, seo, and selu genes found in a specific enterotoxin gene cluster (egc) operon, but without the presence of classical enterotoxins such as SEA ∼ SEE. All egc-positive isolates shared identical pulsed-field gel electrophoresis profiles and were classified under new ST7591 (Clonal Complex 72) with identical spa typing t148. In addition, some isolates of S. aureus obtained from food sources sold in Hangzhou over the past 3 years and carrying egc genes were grouped under the ST72 lineage (CC72). Through whole genome sequencing, a strong genetic connection was revealed between these egc-positive isolates and clinical ST72 S. aureus found in China.

CONCLUSIONS

S. aureus with non-classical egc enterotoxins was suggested to be a potential cause of SFP in humans.

A Rationally Designed CRISPR/Cas12a Assay Using a Multimodal Reporter for Various Readouts

The CRISPR/Cas systems offer a programmable platform for nucleic acid detection, and CRISPR/Cas-based diagnostics (CRISPR-Dx) have demonstrated the ability to target nucleic acids with greater accuracy and flexibility. However, due to the configuration of the reporter and the underlying labeling mechanism, almost all reported CRISPR-Dx rely on a single-option readout, resulting in limitations in end-point result readouts. This is also associated with high reagent consumption and delays in diagnostic reports due to protocol differences. Herein, we report for the first time a rationally designed Cas12a-based multimodal universal reporter (CAMURE) with improved sensitivity that harnesses a dual-mode reporting system, facilitating options in end-point readouts. Through systematic configurations and optimizations, our novel universal reporter achieved a 10-fold sensitivity enhancement compared to the DETECTR reporter. Our unique and versatile reporter could be paired with various readouts, conveying the same diagnostic results. We applied our novel reporter for the detection of staphylococcal enterotoxin A due to its high implication in staphylococcal food poisoning. Integrated with loop-mediated isothermal amplification, our multimodal reporter achieved 10 CFU/mL sensitivity and excellent specificity using a real-time fluorimeter, in-tube fluorescence, and lateral flow strip readouts. We also propose, using artificially contaminated milk samples, a fast (2-5 min) Triton X-100 DNA extraction approach with a comparable yield to the commercial extraction kit. Our CAMURE could be leveraged to detect all gene-encoding SEs by simply reprogramming the guide RNA and could also be applied to the detection of other infections and disease biomarkers.

Identification and molecular mechanism of action of antibacterial peptides from Flavourzyme-hydrolyzed yak casein against Staphylococcus aureus

Antibacterial peptides can be released from yak milk casein. To date, the amino acid sequences and mechanism of action of yak casein-derived antibacterial peptides remain unknown. The current study identified antibacterial peptides from yak casein and their molecular mechanism of action. Our results showed that yak α-casein, β-casein, and κ-casein could be effectively hydrolyzed by Flavourzyme (Solarbio Science and Technology Co. Ltd.), and the 2-h hydrolysate showed the highest antibacterial rate of 43.07 ± 2.59% against Staphylococcus aureus. The 1,000 to 3,000 Da fraction accounted for 23.61% of the 2-h hydrolysate and had an antibacterial rate of 62.64 ± 4.40%. Three novel peptides with antibacterial activity were identified from this fraction, and the β-casein-derived peptide APKHKEMPFPKYP showed the strongest antibacterial effect (half-maximal inhibitory concentration = 0.397 mg/mL). Molecular docking predicted that APKHKEMPFPKYP interacted with 2 important enzymes of Staph. aureus, dihydrofolate reductase and DNA gyrase, through hydrophobic, hydrogen bonding, salt bridge, and π-π stacking interactions. Our findings suggest that the yak casein-derived peptides may serve as a potential source of natural preservatives to inhibit Staph. aureus.

Effect and Mechanism of Eliminating Staphylococcus aureus by Electron Beam Irradiation and Reducing the Toxicity of Its Metabolites

The purpose of this study was to evaluate the mechanism of sterilization of Staphylococcus aureus by electron beam irradiation (0.5-, 1-, 2-, 4-, and 6-kGy treatments) and whether it reduces the toxicity of its fermentation supernatant. In this study, we investigated the mechanism of sterilization of S. aureus by electron beam irradiation using colony count, membrane potential, intracellular ATP, and UV absorbance measurements; we used hemolytic, cytotoxic, and suckling mouse wound models to verify that electron beam irradiation reduced the toxicity of the S. aureus fermentation supernatant. The results showed that 2 kGy of electron beam irradiation treatment completely inactivated S. aureus in suspension culture, and 4 kGy inactivated cells in S. aureus biofilms. This study suggests that the bactericidal effect of electron beam irradiation on S. aureus may be attributed to reversible damage to the cytoplasmic membrane, resulting in its leakage and the significant degradation of genomic DNA. The combined results of hemolytic, cytotoxic, and suckling mouse wound models demonstrated that the toxicity of S. aureus metabolites was significantly reduced when the electron beam irradiation dose was 4 kGy. In summary, electron beam irradiation has the potential to control S. aureus and reduce its toxic metabolites in food. IMPORTANCE Electron beam irradiation of >1 kGy damaged the cytoplasmic membrane, and reactive oxygen species (ROS) penetrated the cells. Electron beam irradiation of >4 kGy reduces the combined toxicity of virulent proteins produced by Staphylococcus aureus. Electron beam irradiation of >4 kGy can be used to inactivate Staphylococcus aureus and biofilms on milk.

Prevalence and Virulence Determinants of Staphylococcus aureus in Wholesale and Retail Pork in Wuhan, Central China

Staphylococcus aureus is one of the major foodborne pathogens and can cause serious foodborne illness in humans by foods contaminated with S. aureus enterotoxins. In recent years, livestock-associated S. aureus has been a major public health concern for humans and has emerged in various countries globally. China is one of the largest producers of pigs and pork in the world. However, there are few studies on the detailed genotypic and pathogenic characterization of pork-associated S. aureus in China. In this study, the prevalence, antimicrobial resistance, and genotypic characteristics of S. aureus in raw pork in Wuhan, China, were investigated through multilocus sequence typing (MLST), staphylococcal protein A gene (spa) typing, and whole-genome sequencing analysis. A total of 518 S. aureus isolates (16.9%) were isolated from 3067 retail and wholesale pork samples. The prevalence of S. aureus in retail pork (22.7%) was significantly higher than in wholesale pork (15.1%), while the proportion of multidrug-resistant (MDR) isolates in wholesale pork (12.9%) was significantly higher than in retail pork (6.2%). Among the isolates, 10.8% were resistant to three or more antibiotics, with higher rates of resistance to penicillin (88.8%) and erythromycin (58.1%). A total of 28 sequence types (STs) were identified in the 518 isolates, and the predominant type was ST7 (57.5%), followed by ST5 (9.1%). In addition, based on the whole-genome sequences of 39 representative strains, 17 spa types were identified among the isolates, of which t899, t091, and t437 were the most common. Furthermore, 19 staphylococcal enterotoxin (SE) and SE-like (SEl) toxin genes were detected in the isolates, of which selw was the most common type (100%), followed by sei, sem, seo, seu, and selv (46.2%); sey (35.9%); and sea, seg, and sen (33.3%). This study found for the first time that ST7-t091-selw and ST9-t899-SCCmecXII-selw were the predominant genotypes of S. aureus in pork in China, which indicated the spreading of S. aureus with multiple virulence factors, especially with new SE/SEl types in pigs and pork, is a serious new challenge for food safety. Good hygiene and good production practices to prevent interspecies transmission and cross-contamination of S. aureus in the pig-pork chain are of great significance to public health.

First Evidence of the Presence of the Causative Agent of Caseous Lymphadenitis-Corynebacterium pseudotuberculosis in Dairy Products Produced from the Milk of Small Ruminants

This study focused on the detection and quantification of selected bacteria and on the presence of enterotoxin genes in milk and dairy products from sheep and goat farms in the Czech Republic using quantitative real-time PCR (qPCR) and multiplex PCR (PCR). The presence of Corynebacterium pseudotuberculosis (CP), Mycobacterium avium subsp. paratuberculosis (MAP), Listeria monocytogenes, Staphylococcus aureus, S. aureus enterotoxin genes and methicillin-resistant Staphylococcus aureus (MRSA) was determined in 18 milk samples, 28 fresh cheeses, 20 ripened cheeses and 14 yoghurts. The serological status of the herds in relation to CP and MAP was taken into account. The most frequently detected bacterium was S. aureus (48.8%), and subsequent PCR revealed 11 MRSA positive samples. The S. aureus enterotoxin genes seg, sei and sec were detected in two goat cheeses. Cheese samples showed a statistically higher risk of SA and MRSA occurrence. CP (8.8%) and MAP (13.8%) were detected by qPCR on two different seropositive farms. Cultivation of qPCR positive CP samples on agar plates supplemented with potassium tellurite showed the presence of viable bacterium. The results obtained confirmed the necessity of monitoring the infectious status of dairy animals and rapid diagnosis of bacterial pathogens in milk and dairy products.

Microcalorimetric Investigations of Reversible Staphylococcal Enterotoxin Unfolding

Staphylococcal food poisoning (SFP) is a common food-borne illness often associated with contamination during food handling. The genes for Staphylococcal enterotoxin (SE) isoforms SEA and SEB are frequently detected in human nasal Staphylococcus aureus isolates and these toxins are commonly associated with SFP. Past studies described the resistance of preformed SE proteins to heat inactivation and their reactivation upon cooling in foods. Full thermodynamic analyses for these processes have not been reported, however. The thermal stabilities of SEA, SEB, and SEH and reversibility of unfolding in simple buffers were investigated at pH 4.5 and pH 6.8 using differential scanning calorimetry (DSC). SEA and SEB unfolding was irreversible at pH 6.8 and at least partially reversible at pH 4.5 while SEH unfolding was irreversible at pH 4.5 and reversible at pH 6.8. Additional studies showed maximum refolding for SEB at pH 3.5–4.0 and diminished refolding at pH 4.5 with increasing ionic strength. SE-stimulated secretion of interferon-gamma by human peripheral blood mononuclear cells was used to assess residual SE biological activity following heat treatments using conditions matching those used for DSC studies. The biological activities of SEB and SEH exhibited greater resistance to heat inactivation than that of SEA. The residual activities of heat-treated SEB and SEH were measurable but diminished further in the presence of reconstituted nonfat dry milk adjusted to pH 4.5 or pH 6.8. To different extents, the pH and ionic strengths typical for foods influenced the thermal stabilities of SEA, SEB, and SEH and their potentials to renature spontaneously after heat treatments.

Effects of citronellal on growth and enterotoxins production in Staphylococcus aureus ATCC 29213

Staphylococcus aureus (S. aureus) is known to be one of the most common foodborne pathogens capable of secreting a wide range of exotoxins such as enterotoxin, which severely threatens the health of consumers. Over the past few years, the development of safe and effective strategies in inhibiting the growth and enterotoxins generation of S. aureus in food turns out to be the research focus and emphasis. This research explores citronellal (CIT), a native compound with extensive existence in spices, which could effectively inhibit the growth and enterotoxins generation of S. aureus (ATCC 29213). Results from minimal inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill curves, showed that CIT could tremendously inhibit the growth of S. aureus. Analysis on hemolysin showed that CIT at sub-MIC could significantly (p < 0.05) inhibit the hemolytic activity of S. aureus. As revealed by the results of ELISA, the production of enterotoxins in the culture supernatant and pork meat decreased significantly (p < 0.05) after exposure to CIT at sub-MIC. Furthermore, a significant (p < 0.05) decrease in dose-dependent was found in the transcription levels of virulence-related genes. In all, CIT proved to be a possible inhibitor of the growth and enterotoxins production of S. aureus with highly promising application in the food industry.

A Carvacrol-Rich Essential Oil Extracted From Oregano (Origanum vulgare "Hot & Spicy") Exerts Potent Antibacterial Effects Against Staphylococcus aureus

Oregano essential oil (OEO), as a natural antimicrobial, has gained increased interest from food researchers and manufacturers. However, a few studies have investigated its possible antibacterial effects against Staphylococcus aureus using the proteomic tool. The present study aimed to explore the antibacterial effect and mechanism of a carvacrol-rich OEO extracted from Origanum vulgare “Hot & Spicy” on the inactivation of S. aureus. The gas chromatography–mass spectrometry analysis of the OEO allowed the detection of 27 compounds; the major constituent was carvacrol (84.38% of total compounds). The average diameter of the inhibitory zone (DIZ) value was 29.10 mm, and the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of OEO against S. aureus were 0.125 and 0.25 mg/mL, respectively. The growth curve assay indicated that the OEO prolonged the lag phase of S. aureus. The decrease in cell viability, changes in the integrity of cell membrane, and abnormal cell morphology further reflected the cell damage of S. aureus caused by the OEO. In addition, a label-free proteomic analysis was applied to analyze the regulatory networks of S. aureus in response to 1/2 MIC OEO-treatment stress. Of the 56 differentially expressed proteins (DEPs) identified, 26 were significantly upregulated and 30 downregulated. The Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis indicated that the DEPs were mainly involved in pathways of ribosomes; valine, leucine, and isoleucine biosynthesis; and phenylalanine, tyrosine, and tryptophan biosynthesis, which suggested that the growth inhibition of S. aureus might be due to the disordered effect of the OEO on protein synthesis and amino acid metabolism. These findings deepened our understanding regarding S. aureus survival and metabolism responses to the OEO treatment and suggested that the carvacrol-rich OEO could be used in food production environments to effectively control S. aureus.