Streptococcus salivarius. Coloured transmission electron micrograph of Streptococcus salivarius bacterial cells. These bacteria form chains which are bound together by the capsular material (brown) seen around each cell. S. salivarius is a Gram-positive, non-motile, spherical bacterium which forms part of the permanent bacterial population of the human mouth. Immune responses from the host, in the form of an antibody attack, are repelled by the bacteria's ability to alter it's surface proteins and thus remain unidentified" by antibodies. Certain strains of S. salivarius can contribute to tooth decay. Magnification: x 82,500 at 6x7cm size. Magnification:x165,000 at 8x10 inch size."