Cryoscanning electron microscopy of a layer of extracellular polysaccharides produced by bacterial colonies

Cryo-SEM allowed observation of a layer of extracellular polysaccharides that covered colonies of the bacterium Pseudomonas aeruginosa, growing on agar substrate. The layer was not found when using conventional preparation techniques and scanning electron microscopy. It disappeared partially as a result of glutaraldehyde fixation, but mainly during alcohol dehydration and critical point drying.