European scientists have developed a method to detect potential biological warfare agents in food.

A possible scenario for a bioterrorism attack could involve food contamination with protein toxins, such as ricin and botulinum neurotoxins, says Brigitte Dorner, researcher into microbial toxins, of the Robert Koch Institute in Berlin. However, until now detecting toxins in such complex samples has been difficult. Dorner and colleagues in Germany and Switzerland have devised a highly sensitive system that can detect trace amounts of the toxins in foods such as milk, baby food and yoghurt.

Protein toxins are detected most effectively using immunological techniques, since antibodies bind to their targets with very high affinity. However, current methods for raising antibodies against toxins without causing animal poisoning are time consuming and labour intensive. Dorner and coworkers have used an alternative technique, immobilising the toxins on microbeads to reduce their toxicity, allowing the team to generate antibodies quickly in vivo. 

Castor bean protein ricin inhibits protein synthesis in the body © USDA-ARS

The researchers then modified a commercially available system to analyse complex food samples using the antibodies. In Luminex xMAP technology antibodies are covalently coupled to beads embedded with dyes that generate signals in response to different targets - in this case the toxins. Dorner explains: 'We further developed the Luminex xMAP technology to incorporate magnetic beads to allow us to analyse complex matrices.' The magnetic property means that the beads can be easily removed from food samples and can undergo automated washings. This makes toxin detection in foods possible where many other technologies have failed due to interference of sample components with binding agents or technical equipment.

Using the bead array, the researchers simultaneously detected trace amounts of five toxins, including ricin and botulinum neurotoxins, in food at lower concentrations than commercially available systems. Dorner says the technique has very good sensitivity. 'We are able to detect toxins down to a level of picograms per millilitre which, as far as I know, is superior to any limit published for other multiplex detection systems,' she says. 

Phillipe Thullier from the Research Centre for Armed Forces' Health in La Tronche, France, is an expert in the field of immunological techniques for toxin detection and neutralisation. He comments: 'The sensitivities are quite unique and to a large extent are made possible by the beads. In the future,' he adds, 'we could see more of these nano objects in biology, used for several purposes.'

Dorner anticipates a possible commercial application for the technique. 'A further step would be introduction of a mobile device using the bead array,' she says, 'and a very nice use of the technique would be large scale screening of the food supply chain.'

Victoria Steven

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