Surface-activated chemical ionization and cation exchange chromatography for the analysis of enterotoxin A.

Surface-activated chemical ionization (SACI) has been widely used in recent years for the analysis of different compounds (e.g. peptides, street drugs, amino acids). The main benefits of this technology are its high sensitivity and its effectiveness under different chromatographic conditions [i.e. ion exchange chromatography and reversed-phase (RP) chromatography]. Here we used SACI in conjunction with quadrupole time-of-flight mass spectrometry to analyze enterotoxin A, which is produced by Staphylococcus aureus, in milk matrix using both RP and ion exchange chromatographies. SACI had increased sensitivity as compared with electrospray ionization. Moreover, the higher quantitation efficiency of this technique, mainly in terms of limit of detection (0.01 ng/ml), limit of quantitation (0.05 ng/ml), linearity range (0.05-50 ng/ml), matrix effect, accuracy (intraday and interday accuracy errors were 9.2% and 10.3%, respectively) and precision (intraday and interday precision errors were 5.3% and 12.8%, respectively), is shown and discussed.

Development of a multiplex PCR assay for the identification of Staphylococcus aureus enterotoxigenic strains isolated from milk and dairy products.

A multiplex PCR for the simultaneous detection of Staphylococcus aureus 23S rRNA, the coagulase and thermonuclease genes as well as the enterotoxin genes sea, sec, sed, seg, seh, sei, sej, sel was developed. The method was used to determine the presence of enterotoxigenic types for 93 S. aureus strains isolated from milk and dairy products. The data obtained by mPCR resulted comparable to those obtained by immunoassay methods. In addition, the mPCR assays also amplified some se genes, whose toxins are undetectable by immunoassay. Multiplex amplification can be obtained starting from 1 pg of DNA, showing the excellent specificity and high sensitivity of the assay.