Streptococcus is a genus of coccus (spherical) gram-positive bacteria belonging to the phylum Firmicutes and the Lactobacillales (lactic acid bacteria) order.owever, many streptococcal species are not pathogenic, and form part of the commensal human microbiota of the mouth, skin, intestine, and upper respiratory tract. Furthermore, streptococci are a necessary ingredient in producing Emmentaler (Swiss) cheese.