Highly Sensitive Suspension Immunoassay for Multiplex Detection, Differentiation, and Quantification of Eight Staphylococcus aureus Enterotoxins (SEA to SEI)

Staphylococcal enterotoxins (SEs) are major contributors to foodborne intoxications. Reliable detection methods for SEs are essential to maintain food safety and protect public health. Since the heat-stable toxins also exert their toxic effect in the absence of the bacterium, reliance on DNA detection alone can be misleading: it does not allow for determining which specific toxins encoded by a given strain are produced and epidemiologically linked with a given outbreak. Commercially available diagnostic assays for SE detection are so far limited in sensitivity and specificity as well as in the range of targeted toxins (SEA-SEE), thus non-targeted SEs linked to foodborne illness remain undetected at the protein level. This study aimed to develop a highly sensitive and specific multiplex suspension immunoassay (SIA) for SEA to SEI. To this end, high-affinity monoclonal antibodies (mAbs) for the specific detection of the individual SEs were generated. When implemented in sandwich ELISAs and multiplex SIA, these mAbs demonstrated exceptional sensitivity with detection limits in the low picogram per millilitre range. When applied for the analysis of SE production in liquid cultures of a panel of 145 whole-genome sequenced strains of <i>Staphylococcus</i> spp. and <i>Enterococcus faecalis</i>, the novel multiplex SIA detected and differentiated the eight SEs with assay accuracies of 86.9-100%. Notably, the multiplex SIA covered one to four sequence variants for each of the individual SEs. Validation confirmed high recovery rates and reliable performance in three representative complex food matrices. The implementation of the novel mAbs in a multiplex SIA enabled, for the first time, simultaneous detection, differentiation, and quantification of multiple SEs from minimal sample volumes using Luminex^® technology. As a result, the multiplex SIA will help strengthen food safety protocols and public health response capabilities.