CNRI / SCIENCE PHOTO LIBRARY CNRI / SCIENCE PHOTO LIBRARY
False-colour transmission electron micrograph (TEM) of the gram-positive bacteria, Streptococcus pneumoniae (the pneumonococcus), associated with pneumonia in humans. The spherical Gram-positive bacteria secrete a viscous material to form a capsule around their cell wall. The role of the capsule is uncertain, but is associated with virulence in pathogenic organisms, conveying protection against the immune system of the host. Capsulated organisms resist phagocytosis (engulfing) by white blood cells and may survive digestion by scavengers cells, continuing to multiply normally. Magnification: x14,000 at 35mm, x 28,000 at 6x7cm size.
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