Rapid and highly specific detection of disease-causing micro-organisms is now possible thanks to US scientists.

Graham Cooks and colleagues at Purdue University took 'fingerprints' of whole cell bacteria in less than 10 minutes using mass spectrometry. Cooks believes the method could be used for the rapid in situ detection of bio-warfare agents and to identify sources of infection in the clinic.

According to Cooks, the main advantage of the detection process, which uses desorption mass spectrometry (DESI), is speed combined with high specificity. 'It provides highly selective fingerprints of the bacterial culture in question,' explained Cooks. 'With identical cultures giving the same fingerprint mass spectrum, closely related strains of bacteria giving similar but differentiable mass spectra and different species giving significantly different mass spectra.' 

The whole cell bacteria tested by the scientists, Escherichia coli and two strains of Salmonella typhimurium, gave reproducible data and showed characteristic fragmentation into various fatty acids and phospholipids.  

The DESI detection process is fast because no sample preparation is necessary whereas existing mass spectrometry-based methods for bacteria analysis require extensive sample preparation.

A future challenge and requirement of the method is to build a library of DESI mass spectra, or 'fingerprints', of different micro-organisms so the content of an unknown sample can be determined. 

As the envisaged applications demand small and cheap equipment, Cooks' team is currently developing a miniature DESI mass spectrometer.  It is approximately the size of a shoe box, said Cooks, and is designed for use in public places and physicians' offices for the in situ detection of hazardous biological molecules. 

Alison Stoddart