Group A Streptococcus pyogenes (GAS) bacteria, coloured scanning electron microscope. GAS (orange) being engulfed by a human neutrophil (teal), a white blood cell. These bacteria, which are Gram-positive and coccus shaped (spherical), are commonly found on the skin and in the throat. They can cause sore throat (strep throat) and soft tissue infections such as impetigo and cellulitis. Occasionally GAS can be a more serious infection known as invasive Group A Streptococcus (iGAS), which can cause bacteremia, septic arthritis and meningitis. GAS can be treated with antibiotics such as penicillin or erythromycin.