A comprehensive review on the detection of Staphylococcus aureus enterotoxins in food samples

Novel strategy for screening aptamers of Staphylococcus aureus enterotoxin A based on active fragments and fusion design

BACKGROUND

Staphylococcus aureus enterotoxin A (SEA) is the major toxin responsible for food poisoning caused by Staphylococcus aureus infection. Aptamers are an ideal solution for visual detection of SEA. However, screening for aptamers is generally expensive and time-consuming. Therefore, a new method for efficient screening of high-affinity SEA aptamers needs to be established and supplemented with smartphone image recognition to enable visual and rapid detection of SEA.

RESULTS

A new aptamer for sensitive detection of SEA was screened using active fragments and fusion design. The novel high-affinity aptamer (BX1) was derived by intercepting active nucleotide fragments of several aptamers and fusing them; it was verified to have high affinity, with a Kd value of 4.16 ± 0.22 nM. Molecular dynamic simulation illustrated that BX1 formed a stable complex conformation with SEA, which maintained its stability for 200 ns. This novel aptamer can be used for visual inspection of SEA. A smartphone-assisted aptasensor was designed to sensitively detect SEA in milk with a wide linear range (1-250 ng/mL), low detection limit (0.42 ng/mL), and satisfactory spiked recovery.

SIGNIFICANCE

A new method for screening SEA aptamers based on active fragments and fusion design was developed, which can rapidly screen high-affinity aptamers in a short duration and at a low expenditure. In addition, a new strategy for the rapid detection of SEA using a smartphone-assisted colorimetric aptamer sensor was successfully applied. This research method may provide a reference for the highly sensitive detection of other biotoxins.

Genomic-transcriptomic analysis of Staphylococcus aureus biofilm formation under sub-MIC antibiotic exposure

Antibiotics are widely used in animal husbandry to ensure the health of livestock, leading to the exposure of microorganisms to accumulated sub-lethal concentrations (sub-MICs) of antibiotics in meats. This study aimed to investigate the effects and mechanisms of sub-MICs of commonly used antibiotics on the biofilm formation of a S. aureus strain Guangzhou-SAU071 which displays weak biofilm formation despite harboring biofilm-associated genes. CV and MTS assays were used to determine biofilm biomass and cell viability, respectively. Dual-omics sequencing combining genomics and transcriptomics was used to study the global expression changes. Expression of biofilm and two-component system associated genes was further verified by RT-qPCR. Biofilm formation of Guangzhou-SAU071 was enhanced under sub-MIC of ciprofloxacin (2 μg/mL) and streptomycin (128 μg/mL). Nearly half of the genes associated with biofilm formation, cell wall anchoring, and two-component systems exhibited significant differential expression under sub-MIC of ciprofloxacin and streptomycin. As concluded, sub-MIC of ciprofloxacin and streptomycin enhanced biofilm formation of S. aureus, possibly due to its regulation on biofilm and two-component system associated genes.

Antimicrobial Resistant Staphylococcus spp., Escherichia coli, and Salmonella spp. in Food Handlers: A Global Review of Persistence, Transmission, and Mitigation Challenges

Antimicrobial resistance in foodborne pathogens represents a critical global health challenge, with food handlers serving as key contributors in their transmission. This comprehensive review synthesizes evidence on the prevalence, transmission dynamics, and antimicrobial resistance patterns of three major pathogens, Staphylococcus spp., Escherichia coli, and Salmonella spp., among food handlers worldwide. Analysis of studies across diverse geographical regions reveals considerable variation in colonization rates, with Staphylococcus spp. prevalence ranging from 19.5% to 95.0%, Escherichia coli from 2.8% to 89.3%, and Salmonella spp. from 0.07% to 9.1%. Resistance profiles demonstrate alarming trends, including widespread β-lactam resistance and emerging resistance to last-resort antibiotics like carbapenems. Particularly concerning is the high occurrence of multidrug resistant (MDR) strains and extended spectrum β-lactamase (ESBL) producers in low- and middle-income countries. This review identified inadequate handwashing, poor hygiene infrastructure, and asymptomatic carriage as critical factors facilitating the transmission of antimicrobial resistant strains. These findings underscore the urgent need for enhanced surveillance systems, targeted decolonization strategies, improved hygiene protocols, and food handler education to mitigate the spread of resistant pathogens through the food chain.

A Highly Sensitive Giant Magnetoresistive (GMR) Biosensor Based on the Magnetic Flux Concentrator Effect

Magnetic biosensors have wide applications in biological target detection due to their advantages such as low background noise, convenient detection, and low requirements for sample pretreatment. However, existing magnetic biosensors still have the drawback of low sensitivity compared to optical and electrochemical biosensors. This paper presents the novel design of a high-sensitivity magnetic biosensor by utilizing the magnetic field line convergence effect, which was applied to bacterial detection. The results indicate that it can achieve a detection limitation of 10 CFU/mL, demonstrating that it can be implemented in high-sensitivity biological target detection.

Introduce a novel, extremely sensitive aptamer against staphylococcal enterotoxin type D

BACKGROUND

Staphylococcus aureus (S. aureus) is a globally prevalent foodborne pathogen responsible for significant public health concerns. Staphylococcal food poisoning (SFP) results from staphylococcal enterotoxins (SEs) produced by specific strains of S. aureus. Rapid and effective detection of SEs remains a significant challenge for public health authorities. Aptamers, short single-stranded DNA(ssDNA), RNA, or synthetic xeno nucleic acid (XNA) molecules, exhibit high affinity for binding to their specific targets. Due to their unique properties, including low production costs, ease of chemical modification, high thermal stability, and reproducibility, aptamers present a viable alternative to antibodies for diagnostic and therapeutic applications.

OBJECTIVES

This research aimed to isolate high-affinity ssDNA aptamers with specificity for staphylococcal enterotoxin D (SED).

METHODS

The systematic evolution of ligands by the exponential enrichment (SELEX) method was utilized to identify specific aptamers. These aptamers were then validated using enzyme-linked apta-sorbent assay (ELASA) and surface plasmon resonance (SPR) to assess their binding characteristics and affinity.

RESULTS

SELEX successfully identified aptamers with strong binding affinity to SED. Among the identified candidates, one aptamer, Aptamer 1, exhibited the highest specificity for SED with a dissociation constant (KD) of 4.4 ± 2.26 nM. The limit of detection (LOD) for SED using this aptamer was determined to be 45 nM.

CONCLUSIONS

The findings indicate that the ELASA system designed using the aptamer developed in this study demonstrates higher specificity, sensitivity, and reproducibility in detecting enterotoxin D. This novel aptamer offers significant potential for applications in diagnostic platforms targeting S. aureus enterotoxins.

A glucan from Ganoderma lucidum: Structural characterization and the anti-inflammatory effect on Parkinson's disease via regulating dysfunctions of intestinal microecology and inhibiting TLR4/MyD88/NF-κB signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Ganoderma lucidum (Curtis) P. Karst (G. lucidum) is a traditional Chinese medicinal fungus, used to exert a beneficial effect on central nervous system, such as Parkinson's disease (PD). Polysaccharide is its main active ingredient, but the structural characterization and the mechanisms of the beneficial effect on PD remain to be elucidated.

AIM OF THE STUDY

To obtain a purified G. lucidum polysaccharide and elucidate its structure, investigate the anti-inflammatory effect on PD and explore its potential mechanisms.

MATERIALS AND METHODS

The structure of polysaccharide was analyzed through methylation analysis and NMR analysis. The anti-inflammatory effect on PD were explored in a MPTP-induced mouse model. A comprehensive microbiota-gut-metabolomics analysis was executed and subsequently deliberated, focusing on the regulation of dysfunctions of intestinal microecology. The potential mechanisms were investigated using a LPS-induced Caco-2 cell model.

RESULTS

A purified glucan, GLPZ-2 was obtained. GLPZ-2 was with triple helical structure and its backbone was found to be primarily composed of 1,6-α-D-Glcp, 1,4-α-D-Glcp, 1,4,6-α-D-Glcp and 1,3,6-β-D-Glcp, with branches at the C-3 and C-4 position by t-α-D-Glcp. PD mice experiments showed that GLPZ-2 could improve motor symptoms, reduce pathological damage and decrease brain protein expression of α-Syn, IL-6, IL-1β and TNF-α. GLPZ-2 also could regulate the gut microbiota and fecal metabolites to restore to normal trend, increase SCFAs content and inhibit TLR4/MyD88/NF-κB pathway in intestine.

CONCLUSIONS

GLPZ-2 exhibits an anti-inflammatory effect on PD, which provide a foundational basis for the application of GLPZ-2 as an effective drug to prevent and delay PD.

Structural Insights Into the Mechanisms of Recognition of Recombinant Full-Length Antibodies for the Detection of Staphylococcus aureus Enterotoxins C1, C2, and C3

Food poisoning caused by Staphylococcus aureus (S. aureus) and its enterotoxins has become a global food safety issue. Herein, three types of Staphylococcal enterotoxins (SE), including SEC1, SEC2, and SEC3, were successfully expressed and immunized in mice to prepare monoclonal antibodies (mAbs). We screened a pair of mAbs 16E12-9B7 from 12 strains that could simultaneously recognize SEC1, SEC2, and SEC3. Furthermore, the genes from hybridoma cells 9B7 and 16E12 were extracted, amplified, and inserted into expression vectors to obtain recombinant antibodies (rAbs), whose affinities were consistent with those of ascites antibodies. The paired rAbs 16E12-9B7 were applied to a gold immunochromatographic strip (GICS) system to enable the rapid detection of SEC1, SEC2, and SEC3 with visual limits of detection (vLOD) of 2, 0.5, and 2 ng/mL in milk samples. Noticeably, we found that hydrogen bonds and salt bridges played a significant role in these antigen-antibody interactions. The key sites for 9B7 were ASN28 and SER31 in complementarity determining region (CDR) and the key sites for 16E12 were SER32 in the 16E12 variable light chain (VL) and ARG100, SER101, and TYR102 in the 16E12 variable heavy chain (VH). The analysis of key rAbs sites has potential in the screening of mutant antibodies.

Magnetic-plasmonic blackbody enhanced lateral flow immunoassay of staphylococcal enterotoxin B

Staphylococcal enterotoxin B (SEB) in food is a serious health risk, making rapid and accurate detection methods essential. Herein, we synthesized a magnetic plasmonic blackbody, Fe3O4@Au/PDA, by coating a gold/polydopamine (Au/PDA) layer onto an Fe3O4 core. This Fe3O4@Au/PDA exhibits broadband absorption, excellent stability, and rapid magnetic response, making it ideal for use as a magnetic separation tool and colorimetric signal amplifier. We integrated Fe3O4@Au/PDA into a lateral flow immunoassay (LFIA) for ultrasensitive SEB detection, combining magnetic enrichment with enhanced colorimetric signal output. The Fe3O4@Au/PDA-based LFIA achieved a detection limit of 0.19 ng/mL, approximately 41 times lower than traditional gold nanoparticle-based LFIA. Its real-world applicability was tested in various food samples (milk, milk powder, apple juice, and lettuce) with recoveries between 82.4 % and 111.2 % and a coefficient of variation below 12.6 %. Collectively, the designed Fe3O4@Au/PDA shows great promise as a novel multifunctional signal amplification label, advancing the design and development of ultrasensitive LFIA for various fields, such as food safety detection.

Ultrasensitive "On-Off" Ratiometric Fluorescence Biosensor Based on RPA-CRISPR/Cas12a for Detection of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a major pathogenic bacterium responsible for bacterial foodborne diseases, making its rapid, specific, and accurate detection crucial. In this study, we develop a ratiometric biosensor based on the recombinase polymerase amplification-clustered regularly interspaced short palindromic repeats/CRISPR associated protein 12a (RPA-CRISPR/Cas12a) system and Eu-metal-organic framework (Eu-MOF) fluorescent nanomaterials for the high-sensitivity detection of S. aureus, combining with RPA for efficient isothermal amplification, this sensor enhances specificity and sensitivity by utilizing the target activation of CRISPR/Cas12a. The Eu-MOF serves a dual function, providing stable red fluorescence as a reference signal and adsorbing FAM-labeled probes for fluorescence quenching, forming a dual-signal system that significantly reduces background interference. This ratiometric design enables accurate and quantitative detection over a wide range (7.9 × 100 to 7.9 × 108 CFU/mL) with a low detection limit of 3 CFU/mL. Overall, with these merits of simplicity, rapid response, high sensitivity, and specificity, this dual-signal biosensor offers a promising method for accurately evaluating S. aureus contamination in food under complex substrate conditions.

Quantification of Staphylococcal Enterotoxin A Variants at Low Level in Dairy Products by High-Resolution Top-Down Mass Spectrometry

Food poisoning outbreaks frequently involve staphylococcal enterotoxins (SEs). SEs include 33 distinct types and multiple sequence variants per SE type. Various mass spectrometry methods have been reported for the detection of SEs using a conventional bottom-up approach. However, the bottom-up approach cannot differentiate between all sequence variants due to partial sequence coverage, and it requires a long trypsin digestion time. While the alternative top-down approach can theoretically identify any sequence modifications, it generally provides lower sensitivity. In this study, we optimized top-down mass spectrometry conditions and incorporated a fully 15N-labeled SEA spiked early in the protocol to achieve sensitivity and repeatability comparable to bottom-up approaches. After robust immunoaffinity purification of the SEA, mass spectrometry signals were acquired on a Q-Orbitrap instrument operated in full-scan mode and targeted acquisition by parallel reaction monitoring (PRM), enabling the identification of sequence variants and precise quantification of SEA. The protocol was evaluated in liquid and solid dairy products and demonstrated detection limits of 0.5 ng/mL or ng/g in PRM and 1 ng/mL or ng/g in full-scan mode for milk and Roquefort cheese. The top-down method was successfully applied to various dairy products, allowing discrimination of contaminated versus non-contaminated food, quantification of SEA level and identification of the variant involved.

Enhanced immunochromatographic assay using multifunctional gold@iridium nanoflower with colorimetric photothermal catalytic activity for the detection of staphylococcal enterotoxin B

The development of a rapid, sensitive, and accurate screening method for staphylococcal enterotoxin B (SEB) in food is urgently needed because trace amounts of SEB can pose a serious threat to human health. Here, we developed a ultrasensitive triple-modal immunochromatographic assay (ICA) for SEB detection. The AuNFs@Ir nanoflowers exhibited enhanced colorimetric, photothermal, and catalytic performance by modulating the sharp branching structure of the gold nanoflowers and depositing high-density Ir atoms. Subsequently, the combination of AuNFs@Ir and ICA promoted colorimetric, catalytic amplified colorimetric, and photothermal-assisted quantitative detection. The results showed detection limits of 0.175, 0.0188, and 0.043 ng mL-1 in the colorimetric/photothermal/catalytic mode, which increased the sensitivity by 16.5-fold, 153.7-fold, and 67.2-fold, respectively, compared with the AuNPs-ICA. Furthermore, the proposed strategy was verified in milk, milk powder, pork, and beef successfully. This strategy improves significantly the sensitivity, accuracy, flexibility and offers an effective insight for foodborne bacterial toxin monitoring.

Phage LysSA163-CBD mediated specific recognition coupled with ATP bioluminescence for the sensitive detection of viable Staphylococcus aureus in food matrices

BACKGROUND

Staphylococcus aureus is a significant foodborne pathogen, commonly detected in milk and meat products. Conventional detection methods have limited sensitivity and specificity, which are time-consuming and susceptible to background interference from complex samples, and cannot effectively distinguish live and dead bacteria.

RESULTS

Herein, we developed a novel adenosine triphosphate (ATP) bioluminescence method coupled with magnetic separation, which is based on phage-encoded endolysin LysSA163-CBD (CBD 163) for rapid and specific detection of viable Staphylococcus aureus. The expressed protein (CBD 163) was derived from the phage LSA2301 and was successfully expressed in Escherichia coli BL21 following an induction period of 4 h at 37 °C, with a molecular weight approximating 40 kDa. The optimal conditions for CBD-magnetic beads (cMBs) to capture S. aureus cells were determined to be 100 μL/mL cMBs at 25 °C for 30 min. The viable S. aureus cells were disrupted by the Cetyl trimethyl ammonium bromide (CTAB) to release intracellular ATP. Then, the ATP reacted with the firefly luciferase and D-Luciferin-based bioluminescence (BL) reagents solution to generate intensive BL signal. The CBD-magnetic separation-ATP bioluminescence (cMS-BL) assay was able to quickly detect viable S. aureus via ATP bioluminescence in 45 min, with a detection range from 5 × 103 to 5 × 107 CFU/mL and limit of detection (LOD) of 190 CFU/mL. Additionally, the cMS-BL method exhibited high specificity and anti-interference ability, which has been successfully applied to quantify S. aureus cells in crayfish-tail, chicken, and skim milk.

SIGNIFICANCE AND NOVELTY

These results demonstrate the potential of CBD 163 as a versatile and robust biorecognition element for rapid and specific detection of viable S. aureus in food matrices. The proposed phage-derived bacteria-binding proteins-based protocol for BL detection shows various advantages, including high sensitivity, simple operation, and the capability to distinguish live bacteria, providing a strategy for designing high-quality biorecognition element toward foodborne pathogens.

Target Recognition-Triggered Interfacial Electron Transfer Model: Toward Signal-On Photoelectrochemical Aptasensing for Efficient Detection of Staphylococcus aureus Using Ti3C2Tx-Au NBPs/ZnO NR Composites

Staphylococcus aureus (S. aureus) is one of the most common foodborne pathogens worldwide, which poses a great threat to public health. It is of utmost importance to develop rapid, simple, and sensitive methods for the determination of S. aureus. A signal-on photoelectrochemical (PEC) aptasensor is constructed herein based on titanium carbide (Ti3C2Tx)-Au nanobipyramids (NBPs)/ZnO nanoarrays (NRs). The reliability and capability of the PEC aptasensor make it suitable for the sensitive and selective determination of S. aureus. First, the electrostatically self-assembled Ti3C2Tx-Au NBP nanomaterial was coated on the ZnO NR surface by a spin-coating method. On the one hand, Ti3C2Tx-Au NBPs can broaden the spectral absorption of ZnO NRs, resulting in Ti3C2Tx-Au NBPs/ZnO NR composites that exhibit a wide range of absorption from the ultraviolet to the infrared region. On the other hand, Ti3C2Tx can reduce the agglomeration of nanoparticles, while Au NBPs can effectively fix the aptamer through the Au-S bond. Specifically, the experimental results show that when S. aureus is present, the Au NBPs-aptamer-S. aureus complex is shed from the electrode surface, altering the interfacial electron transfer model and reducing the steric hindrance. Consequently, an amplified photocurrent signal for the quantitative determination of S. aureus is obtained. Under optimal experimental conditions, a linear correlation is observed between the current response of the aptasensor and the logarithm of the S. aureus concentration (ranging from 1.0 to 1.0 × 106 CFU/mL), with an impressive detection limit as low as 0.5 CFU/mL. Furthermore, the aptasensor has been successfully employed for the detection of S. aureus in milk, with the recovery of 93.0%-99.0%. Hence, this research offers a novel approach for the detection of foodborne pathogens and other noxious substances.

Staphylococcus aureus in Dairy Industry: Enterotoxin Production, Biofilm Formation, and Use of Lactic Acid Bacteria for Its Biocontrol

Staphylococcus aureus is a well-known pathogen capable of producing enterotoxins during bacterial growth in contaminated food, and the ingestion of such preformed toxins is one of the major causes of food poisoning around the world. Nowadays 33 staphylococcal enterotoxins (SEs) and SE-like toxins have been described, but nearly 95% of confirmed foodborne outbreaks are attributed to classical enterotoxins SEA, SEB, SEC, SED, and SEE. The natural habitat of S. aureus includes the skin and mucous membranes of both humans and animals, allowing the contamination of milk, its derivatives, and the processing facilities. S. aureus is well known for the ability to form biofilms in food processing environments, which contributes to its persistence and cross-contamination in food. The biocontrol of S. aureus in foods by lactic acid bacteria (LAB) and their bacteriocins has been studied for many years. Recently, LAB and their metabolites have also been explored for controlling S. aureus biofilms. LAB are used in fermented foods since in ancient times and nowadays characterized strains (or their purified bacteriocin) can be intentionally added to prolong food shelf-life and to control the growth of potentially pathogenic bacteria. Regarding the use of these microorganism and their metabolites (such as organic acids and bacteriocins) to prevent biofilm development or for biofilm removal, it is possible to conclude that a complex network behind the antagonistic activity remains poorly understood at the molecular level. The use of approaches that allow the characterization of these interactions is necessary to enhance our understanding of the mechanisms that govern the inhibitory activity of LAB against S. aureus biofilms in food processing environments.

Transcriptomic and Biochemical Analysis of the Antimicrobial Mechanism of Lipopeptide Iturin W against Staphylococcus aureus

Staphylococcus aureus is one of the most serious pathogens threatening food safety and public health. We have previously showed that iturin W exhibited obvious antifungal activity on plant pathogens. In the present study, we found iturin W, especially C14 iturin W, showed strong antimicrobial activity against S. aureus, and the antimicrobial mechanism of C14 iturin W was further investigated by transcriptomic analysis and a related biochemical experiment. The results showed that C14 iturin W can reduce the expression levels of genes associated with the reactive oxygen species (ROS) scavenging enzyme and genes involved in arginine biosynthesis, thus leading to the increase in ROS levels of S. aureus. Furthermore, C14 iturin W can also interfere with proton dynamics, which is crucial for cells to regulate various biological possesses. Therefore, ROS accumulation and change in proton motive force are import ways for C14 iturin W to exert the antimicrobial activity. In addition, C14 iturin W can also reduce the expression levels of genes related to virulence factors and decrease the production of enterotoxins and hemolysins in S. aureus, indicating that C14 iturin W has a good potential in food and pharmaceutical fields to reduce the harm caused by S. aureus in the future.

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.