Light micrograph of colony of Streptococcus pyogenes, a species of gram-positive, non-motile, spherical bacterium that occur in chains. S. pyogenes is pathogenic and haemolytic (ie it has the ability to destroy red blood cells in blood agar culture - a useful factor in identifying the numerous strains that occur). Various strains of S. pyogenes are associated with numerous infections, including scarlet fever; they also produce exotoxins, potent poisons that are harmful to a limited range of tissues, and are secreted by the bacterium into the surrounding media. Mag: x400 at 6x4.5cm size, x254 at 35mm size.