A 16-year-old teenager complains about halitosis, general weakness, body temperature rise up to 37,6°C. These symptoms turned up two days ago, the boy had a history of recent angina. Objectively: oral hygiene is unsatisfactory, the teeth are coated with soft dental deposit. Gums are hyperemic, gingival papillae are covered with greyish deposit. Specify the causative agent of this disease: