Detection of the staphylococcal toxins

Growth and Modeling of Staphylococcus aureus in Flour Products under Isothermal and Nonisothermal Conditions

This study was conducted to investigate the growth of Staphylococcus aureus in traditional Chinese flour products under isothermal (10, 15, 20, 25, 30, and 37°C) and nonisothermal (10 to 20, 20 to 30, and 25 to 37°C) conditions. Then, models for the growth of S. aureus in flour products as a function of storage temperature, pH, and water activity (a_w) were developed, and the goodness of fit of models was evaluated using the determination coefficient (R²), root mean square error (RMSE), bias factor (B_f), and accuracy factor (A_f). Based on the above information, S. aureus growth in steamed bread under nonisothermal conditions was predicted from experiments performed under isothermal conditions. It was shown that different combinations of temperature and a_w in flour products have a strong influence on the growth of S. aureus . The modified Gompertz model was found to be more suitable for describing the growth data of S. aureus in flour products, with an R² of >0.99 and an RMSE of <0.37. The newly developed secondary models were validated, and for the specific growth rate and the lag time, the R² values were 0.96 and 0.97, A_f was 1.12 and 1.06, and B_f was 1.13 and 1.05, respectively. The predicted nonisothermal growth curves of S. aureus were in agreement with the reported experimental ones, with RMSE <0.29, A_f value 1.02 to 1.09, and B_f value 0.92 to 0.99. These results indicated that the predictive models provided useful information for the establishment of safety standards and a risk assessment for S. aureus in flour products.

[Molecular cloning, expression, and characterization of human mini-antibodies against enterotoxin C1 of Staphylococcus aureus]

We describe here the cloning, expression, and production of specific single-chain antibodies (scFv) against the recombinant enterotoxin C1 of Staphylococcus aureus. High-affinity scFv were selected from the phage library of human mini antibodies; afterwards, the cells of E. coli trxA gor double mutant were infected with a product obtained by fusion of DNA encoding of these mini antibodies with the trxA gene to induce soluble scFv synthesis in cell cytoplasm. The scFv obtained displayed high enterotoxin C1 affinity. Analysis for cross reactivity showed that mini-antibodies interacted also with SEA- SEB-, SED-, SEE-, SEG-, and SEI-type enterotoxins, but they failed to interact with ricin, diphtheritic, and cholera toxins, or with both lethal and protective factors of the anthrax toxin. This property may be helpful in screening for staphylococcus enterotoxins.

Surface plasmon resonance analysis of staphylococcal enterotoxin B in food

Surface plasmon resonance (SPR) biosensors are electro-optical instruments used for analyzing real-time protein-protein interactions. This work evaluates an SPR biosensor (Biacore 3000) in the detection of staphylococcal enterotoxin B (SEB) in foods. A sandwich SPR immunosensor involving two antibodies was used. The capturing antibody, bound covalently to the surface of the biosensor chip, performs the initial binding of the antigen and a second antibody binds to the captured antigen. The second antibody makes antigen verification possible and amplifies the signal. Pure SEB as well as SEB in spiked foods (milk and meat) were detected with little interference from the food matrix. In the control experiments with uncontaminated food samples no significant signal was detected. The SPR biosensor assay detects SEB at approximately10 ng/ml rapidly, with initial binding within 2 min. The entire measurement cycle (including washing and chip regeneration) may take 5 min using one antibody or 8 min using two antibodies. These results suggest that the SPR biosensor may be a useful tool for real-time analysis of toxin in foods.

Multitoxin biosensor-mass spectrometry analysis: a new approach for rapid, real-time, sensitive analysis of staphylococcal toxins in food

Biomolecular interaction analysis mass spectrometry (BIA-MS) was applied to detection of bacterial toxins in food samples. This two-step approach utilizes surface plasmon resonance (SPR) to detect the binding of the toxin(s) to antibodies immobilized on a surface of a sensor chip. SPR detection is then followed by identification of the bound toxin(s) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Staphylococcal enterotoxin B (SEB) was readily detected in milk and mushroom samples at levels of 1 ng/ml. In addition, non-specific binding of food components to the immobilized antibody and to the sensor chip surface was detected. To evaluate the applicability of BIA-MS in the analysis of materials containing multiple toxic components, sample containing both SEB and toxic-shock syndrome toxin-1 was analyzed. Both toxins were successfully and simultaneously detected through the utilization of multiaffinity sensor chip surfaces.