The bacterium that causes legionnaire’s disease is difficult to isolate and identify from the body because it

The pathogen behind it was identified as a bacterium called Legionella pneumophila that proliferates in systems of standing water at temperatures between 25 and 50 °C, such as water reservoirs, boilers, fountains, whirlpool tubs, or intermittently used water pipes. Although drinking the contaminated water poses no risk, inhaling droplets leads to severe lung infection. However, traditional testing methods based on bacterial cultures require 10 days to identify the pathogen – far too late to intervene in suspected cases. In Legionella pneumophila, these contain a special saccharide building block that other bacteria do not have. For their new test, the researchers exposed the sample to a precursor molecule of this saccharide with an additional azide group tacked on. If the bacteria in question are present, they take up this substance and use it to build the saccharide building block to use in their lipopolysaccharides—which are now tagged with azide groups. These groups can then be used to attach various probes to the surface of the cell