melissococcus melissococcus melissococcus is a genus of gram-positive, catalase-negative, coccus-shaped lactic acid bacteria within the family enterococcaceae. melissococcus species were classified as streptococcus until 1983 when melissococcus was recognized as a distinct genus. notable species include m. plutonius, which is a cause of european foulbrood (an infectious disease that primarily affects honeybees). melissococcus scientific classification domain: bacteria phylum: bacillota class: bacilli order: lactobacillales family: enterococcaceae genus: melissococcus(ex white, 1912)bailey and collins, 1983 species m. plutonius