The sugars coating bacteria can change very quickly during the course of an infection, cloaking the bacteria from the immune system of their host. Previous techniques for studying the sugars were too slow to catch these rapid changes.
"There's a growing recognition of the importance of carbohydrates on bacterial cell surfaces," says Dr. Lara Mahal, lead researcher and assistant professor of chemistry and biochemistry with the Institute for Cellular and Molecular Biology. "The carbohydrate coating is critical in how your immune system recognizes bacteria."
Mahal and graduate student Ken Hsu report their findings in the advance on-line edition and March issue of Nature Chemical Biology.
The scientists studied the sugar coats of four strains of bacteria: two lab strains of E. coli, one pathogenic strain of E. coli that causes neonatal meningitis, and Salmonella typhimurium, which causes food poisoning.
They analyzed each strain of bacteria using lectin microarrays--small glass plates covered with dots of sugar-binding proteins called lectins. The lectin dots act like microbe Velcro. Bacteria with a surface sugar that matches a specific lectin stick to that lectin dot. Because the bacteria are fluorescently labeled, Mahal and her colleagues can read the patterns of glowing dots and determine which sugars coat the bacteria.
The microarray technique worked fast enough that the researchers were able to see the sugar coating change over time in the neonatal meningitis strain of E. coli.
"Over time, the lectins lost their ability to see these bacteria," says Mahal. "This demonstrates that our system is able to see a dynamic change in the carbohydrates on bacteria surface over time."
Mahal says the microarray method could prov ide an important tool for identifying bacteria and diagnosing infection. It will also provide a way for scientists to start asking questions about the role that surface sugars play in bacterial infection and symbiotic relationships.