A photomicrograph of streptococci bacteria with methylene blue stain The genus Streptococcus is comprised of a wide variety of both pathogenic and commensal gram positive bacteria which are found to inhabit a wide range of hosts including humans horses pigs and cows Within the host streptococci are often found to colonize the mucosal surfaces of the mouth nares and pharynx However in certain circumstances they may also inhabit the skin heart or muscle tissue Pathogenic streptococci of man include S pyogenes S pneumoniae and S faecalis Among the pathogenic haemolytic streptococci S pyogenes or group A streptococci has been implicated as the etiologic agent of acute pharyngitis strep throat impetigo rheumatic fever scarlet fever glomerulonephritis and invasive fasciitis
