Immunological detection of Cronobacter and Salmonella in powdered infant formula by plasmonic label-free assay.

UNLABELLED: Cronobacter is an emerging food pathogen, especially in infants and neonates, often associated with the ingestion of contaminated Powdered Infant Formula (PIF). Therefore, regulations require the control of the absence of Cronobacter and of Salmonella, another important food pathogen, in these food products. So far, reference and alternative methods take up to several days, and no validated method exists for the simultaneous detection of these two pathogens. In this work, we propose to address this issue by an innovative and easy-to-operate assay, named Plasmonic Immuno-Assay (PlasmIA), and by producing dedicated polyclonal antibodies. Our approach is based on Surface Plasmon Resonance imaging of antibody-arrays and bacterial growth during a standardized enrichment. Such a single-step assay enables the multiplex detection of both Cronobacter and Salmonella, with concentrations smaller than 30 CFU cells in 25 g PIF samples, in less than 1 day. SIGNIFICANCE AND IMPACT OF THE STUDY: Among bacterial pathogens involved in food contamination, Cronobacter and Salmonella are of particular interest. Nevertheless, all detection methods used so far require several days to assess food safety. In the present paper, we describe the first multiplex immuno-assay ever described for fast and specific detection of these two pathogens in food samples. Such advances were made possible by combining the advantages of protein microarrays with on-biochip culture of contaminated food samples and an easy-to-operate optical detection. By doing so, we managed to detect both viable Cronobacter and Salmonella occurring during the enrichment phase.

Fast detection of both O157 and non-O157 shiga-toxin producing Escherichia coli by real-time optical immunoassay.

UNLABELLED: Among bacterial pathogens involved in food-illnesses, seven serogroups (O26, O45, O103, O111, O121, O145 and O157) of Shiga-toxin producing Escherichia coli (STEC), are frequently identified. During such outbreak, and due to the perishable property of most foodstuff, the time laps for the identification of contaminated products and pathogens is thus critical to better circumvent their spread. Traditional detection methods using PCR or culture plating are time consuming and may present some limitations. In this study, we present a multiplexed immunoassay for the optical detection of most commonly enterohemorrhagic E. coli serogroups: O26, O45, O103, O111, O121, O145 and O157:H7 in a single device. The use of Surface Plasmon Resonance imaging not only enabled the label-free analysis of the samples but gave results in a real-time manner. A dedicated protocol was set up for the detection of both low contaminating bacterial concentrations of food samples (5 CFU per 25 g) and postenrichment aliquots. By combining one single device for the detection of O157 and non-O157 STEC in a label-free manner, this rapid approach may have an important economic and societal impact. SIGNIFICANCE AND IMPACT OF THE STUDY: This article presents a simple-to-operate immunoassay for the specific detection of Shiga-toxin producing Escherichia coli (STEC). This approach consists in the on-chip assay detection of viable cells on a specifically designed antibody microarray. By skipping any enrichment step and avoiding the use of labelling agent, this approach based on the Surface Plasmon Resonance imaging of the microarrays turns out to be much faster and more cost effective by comparison with standardized methods.