Immuno-transmission electron microscopy. Affinity-purified IgG was prepared from antiserum to isolated EPS made in rabbits, and incubated with whole cells that were gently scraped off plates, followed by Protein-A gold particles. The dark particles binding to the extracellular matrix (arrows) are Protein A-gold particles binding to immunoglobulins. Note that none of the Protein A-gold particles bound to the cell membrane, but were bound to extracellular material shed from the cell. More of this extracellular material was present when cells were grown anaerobically (left) than when cells were grown in CO2 (right).