A 12-year-old child complains of body temperature rise up to 39,8°C, weakness, headache and pain in throat getting worse when swallowing. Objectively: mucous membrane of gums is edematic, hyperemic. Tonsils are bright red, hypertrophic, covered with yellow-gray deposit which does not extend beyond the lymphoid tissue and can be easily removed. Submandibular, occipital lymph nodes are significantly enlarged, slightly painful on palpation. Hepatosplenomegaly is present. Identify the causative agent of this disease: