Researchers at Purdue University in West Lafayette, Ind., have used a new technique to rapidly identify bacteria, including E. coli, without the time-consuming sample preparation typically required.



The technique, called desorption electrospray ionization, or DESI, could be used to create a new class of fast, accurate detectors for applications ranging from food safety to homeland security, says R. Graham Cooks, a chemistry professor.

Using a mass spectrometer to analyze bacteria and other microorganisms ordinarily takes several hours and requires lengthy sample preparation. The new technique the pretreatment steps, enabling researchers to take "fingerprints" of bacteria in less than a minute using a mass spectrometer.

"This is the first time we've been able to chemically analyze and accurately identify the type of bacteria using a mass spectrometer without any prior pretreatment within a matter of seconds," Cooks says.

Mass spectrometry works by turning molecules into ions, or electrically charged versions of themselves, inside the instrument's vacuum chamber. Once ionized, the molecules can be more easily manipulated, detected and analyzed based on their masses.

Purdue researchers are focusing on three potential applications: food safety, medical analysis and homeland security.

The researchers are able to detect one nanogram, or a billionth of a gram, of a particular bacterium. More importantly, the method enables researchers to identify a particular bacterium down to its subspecies, a level of accuracy needed to detect pathogens, such as the aggressive E. coli O157:H7 strain. The identifications are based on specific chemical compounds, called lipids and fatty acids, in the bacteria.