Plague detector: Sweet solution

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  • Published: Aug 1, 2013
  • Author: David Bradley
  • Channels: NMR Knowledge Base
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Antibody assay

Anti-carbohydrate antibodies can be used to identify the presence of the pathogen that causes the deadly disease we know as plague, Yersinia pestis. Credit: Wiley/Angewandte

Anti-carbohydrate antibodies can be used to identify the presence of the pathogen that causes the deadly disease we know as plague, Yersinia pestis.

The lay perception of plague is that it is an ancient disease that no longer matters in the world of modern healthcare. However, Y pestis remains present in several parts of the world and is very much an ongoing threat to human health. The bacterium causes three manifestations of illness: bubonic plague, pneumonic plague and septicaemic plague. Bubonic plague is perhaps the most familiar it being associated with The Black Death that claimed the lives of at least a third of the population of Europe during the 14th Century. When inhaled as an aerosol it causes pneumonic plague, which usually results in death if it is not treated quickly.

However, all three forms have been the cause of widespread mortality throughout human history. 200 million people have died in three major pandemics in Europe during the last 1500 years. More recently, cases of plague have been detected in Africa and Asia. Because of the high danger of transmission and the severity of the infection, Y pestis, is classified as a category A biological weapon. Its existence thus represents a serious biological warfare or terrorism risk.

Case history

There are even now thousands of cases of plague reported to the World Health Organisation (WHO). The frontline treatment involves administering antibiotics such as streptomycin, chloramphenicol, tetracycline and fluoroquinolones, and others including doxycycline and gentamicin have known activity against the pathogen. However, many patients present with severe symptoms and require circulatory and ventilation support and kidney dialysis. The detection of the microbe in samples at the earliest stages is vital when faced with the potential spread of this lethal disease.

Now, Peter Seeberger of the Max Planck Institute of Colloids and Interfaces in Potsdam, Germany, and colleagues have developed a new antibody-based detection method for detecting Y pestis. They used nuclear magnetic resonance (NMR) spectroscopy as part of an arsenal of techniques in their work.They explain that the new sensitive test can be used to identify plague in patient serum and other biological samples reliably. Fundamentally, the antibody recognizes a particular carbohydrate structure found on the cell surfaces of the bacterium with high specificity. The research team offers details of their approach in the Wiley journal Angewandte Chemie.

“Currently, Y pestis is detected by polymerase chain reaction based assays or traditional phenotyping,” explains Seeberger. “These methods of detection are reliable, but they are also often complex, expensive, and slow.” Antibody approaches that recognise surface proteins have been investigated but these too, while promising, have so far shown a high failure rate and low selectivity with regard to related strains of bacteria.

Pest

Seeberger and his team realised that they might be able to develop a much more specific test for Y pestis by focusing on the lipopolysaccharides (LPSs), comprising fatty molecules and carbohydrate that are present on the outer cell membrane of Gram-negative bacteria such as Y pestis. “The inner core of the Yersinia LPS has a unique structure that differs from that of other Gram-negative bacteria,” explains Seeberger. “This could be a suitable region for detection by means of specific antibodies for rapid point-of-care diagnosis.”

Isolation of Y pestis LPS from a sample is, unfortunately, a laborious undertaking, so the researchers chose to synthesise one typical motif from the molecule, a segment consisting of three sugar molecules, triheptoses, to diphtherietoxoid CRM197, which acts as a carrier protein. This protein is a typical component of licensed vaccine formulations and is known to trigger the rapid formation of antibodies. The researchers could thus inoculate mice in the laboratory and using them as living factories for the antibodies to the synthetic Y pestis LPS. The antibodies could be readily extracted from the blood of the mice.

The team then carried out various immunoassays to demonstrate that the resulting antibodies are able to detect the presence of the plague pathogen with high selectivity and sensitivity in different samples. Moreover, the test could differentiate between Y pestis and other Gram-negative bacteria. The team now hopes to develop the same test for direct patient diagnosis of infection and is currently focusing on this work to bring a simple and straightforward plague test to the clinic.

Related Links

Angew Chem Int Edn 2013, online: "Plague Detection by Anti-carbohydrate Antibodies"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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