For microscopic analysis, both, γ-PGA and purified MNV were conjugated with biotin on the exposed amine group using Sulfo-NHS-LC-Biotin (EZ-Link; Pierce, Rockford, IL, USA) according to the manufacturer’s protocol. Biotinylated γ-PGA and MNV-1 were detected using Qdot 625 streptavidin conjugate (Invitrogen).