The overwhelming majority is purulent - inflammatory diseases cause cocci, i.e. microorganisms having the spherical (spherical) form. Them divide on two greater groups - grampositive and gramnegative. Inside of these groups allocate aerobic and facultatively - anaerobic cocci and anaerobic cocci.

Among grampositive aerobic and facultatively - anaerobic cocci the greatest value microorganisms of family Micrococcaceae (sort Staphylococcus) and have families Streptococcaceae (sort Streptococcus), among gramnegative aerobic and facultatively - anaerobic cocci - representatives of family Neisseriaceae (N.gonorrhoeae - honococc and N.meningitidis - meningococcus). Among grampositive anaerobic coccus the greatest value have peptococcus и пептострептококки, among gramnegative anaerobic coccus - veillonell.