Dumont et al. described a new technique to label specifically membranes of culturable Gram negative bacteria, via click chemistry reaction, by assimilation of an azido analogue of Kdo (Kdo-N3), which is a lipopolysaccharide (LPS) essential component.
List of Gram negative bacteria tested:
Alexa® alkyne Click
 Dumont A., Malleron A., Awwad M., Dukan S., Vauzeilles B., Click-Mediated Labeling of Bacterial Membranes through Metabolic Modification of the Lipopolysaccharide Inner Core, Angew. Chem. Int. Ed., 2012, 51, 3143.