Scientists in Germany and Denmark have developed two complementary techniques to examine how bacteria cause infections. 

Bacterial infections such as meningitis and respiratory tract infections constitute a major global health problem, especially for young children. Bacteria cause infections by sticking to sugars on the surface of target cells. These adhesion mechanisms are complex and convenient techniques are needed to evaluate and prevent them. 

Two common assays to investigate the bacteria's binding use either guinea pig blood or ELISA technology, where a series of antibodies and an enzyme detect binding. But these techniques are not ideal as the first does not allow testing of adhesion to surfaces and in the second different antibodies are needed for each different application and the binding cannot be directly detected, explains Thisbe Lindhorst at the Otto Diels Institute of Organic Chemistry, Kiel, Germany.

Lindhorst and colleagues have created new in vitro tools that use plates coated with sugar mannose, mimicking a cell's surface, and two different methods of detecting adhered bacteria. The new methods are 'more like in real biology, with adhesion to surfaces [which can be compared with cells],' says Lindhorst.

The first method uses the molecule biotin to label E. coli bacteria, which are allowed to bind to either the surface or inhibitor in solution. An oxidising enzyme linked to a protein with high affinity for biotin can then be added and the bacteria binding can be detected by the change in the light absorbance caused by enzyme oxidation of an added substrate. The second assay enables direct detection of the binding, by growing bacteria tagged with green fluorescent protein that can be detected directly by the fluorescence readout. 

Both tools are more reproducible than the ELISA method, with the fluorescence-based assay also being faster and very user-friendly, says Lindhorst. Using their assays the group showed that binding to sugar ligands in solution is significantly different from that to immobilised ligands. 'This is of enormous importance when conclusions about the in vivo situation are drawn,' says Lindhorst. 

Terri Camesano, who studies bacterial adhesion at Worcester Polytechnic Institute, US, agrees that this last finding is particularly interesting. She also states that binding of E. coli to carbohydrate receptors is a critical step in the development of urinary tract infections and these assays could enable different blockers to be tested very easily. 'This will have important implications for urinary tract infection research, as well as in more broad development of biosensors,' she adds. 

Frances Galvin

Enjoy this story? Spread the word using the 'tools' menu on the left or add a comment to the Chemistry World blog.