Melissococcus

Melissococcus is a genus of Gram-positive, non-spore-forming cocci that is most notable for its association with honey bees. The best-known member, Melissococcus plutonius, is the etiological agent of European foulbrood (EFB) in honey bee colonies. The genus has historically been described among lactic acid bacteria, and members tend to be fastidious, often requiring enriched media and reduced oxygen for growth.

In honey bees, Melissococcus plutonius infects bee larvae during larval development, leading to larval death and disrupted brood patterns within the comb. Infected brood is typically discolored and desiccated, and colonies weakened by EFB may exhibit reduced brood viability and irregular brood patterns. The disease is primarily observed in managed Apis mellifera colonies and can spread within a hive via contaminated brood food and through beekeeping equipment.

Ecology and epidemiology: European foulbrood occurs worldwide wherever managed honey bees are kept. Transmission within colonies is largely through nurse bees feeding infected larvae, and the organism can be introduced or spread via contaminated equipment or hive materials. Outbreaks are influenced by colony health, nutrition, temperature, and management practices that affect hygiene and brood rearing.

Diagnosis and management: Clinical signs in brood are supplemented by laboratory confirmation, including isolation of M. plutonius from infected larvae or molecular detection by PCR. There is no universally effective curative treatment; emphasis is on hive sanitation and management to limit spread. Practices include removing and destroying infected combs, requeening when appropriate, and maintaining strong colonies. In many jurisdictions, antibiotic use is restricted due to honey residue concerns, underscoring the importance of preventive beekeeping and hygienic practices.

Taxonomy: Melissococcus comprises several species, with M. plutonius being the primary honey bee pathogen associated with European foulbrood. Molecular studies have refined the taxonomy and understanding of related species within the genus.