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For the settlement in Algeria, see M'Lili.
Scientific classification
Domain: Bacteria
Phylum: Firmicutes
Class: Bacilli
Order: Bacillales
Genus: Gemella
Berger 1960

G. bergeri
G. cuniculi
G. haemolysans
G. morbillorum
G. palaticanis
G. sanguinis

Gemella is a genus of Gram-positive bacteria that thrive best at high partial pressure of CO2.


A Gemella species was first described as Neisseria hemolysans in 1938.[2] It was reclassified as a new genus in 1960 when strains were found to be distinct enough from Neisseria to require a new genus.[3] The name was suggested based on the organism being a diplococcus and gemellus is the diminutive of geminus,[4] which is Latin for twin. They are facultatively anaerobic and give negative reactions to both oxidase and catalase tests. They are obligately fermentative, producing either a mixture of acetic and lactic acids or an equimolar molar mixture of acetic acid and CO2. For example, G. haemolysans ferments glucose forming a mixture of acetic and lactic acids in the absence of oxygen, whereas when oxygen is present, it forms acetic acid and CO2.[5]

Clinical importance[edit]

Gemella bacteria are primarily found in the mucous membranes of humans and other animals, particularly in the oral cavity and upper digestive tract. Gemella haemolysans has been found to be involved in pulmonary exacerbations of cystic fibrosis patients.[6] As of the year 2000 it had been reported in 15 cases of human endocarditis, mainly in men with underlying valvular disease and/or poor dentition or dental manipulation. Most cases were treated with a combination of penicillin and gentamicin with a favorable outcome.[7]


  1. ^ Euzéby, J. P. "List of Prokaryotic Names with Standing in Nomenclature". Retrieved 2008-12-16. 
  2. ^ Thjötta (1938). "Neisseria hemolysans. A Hemolytic Species of Neisseria trevisan". Acta Path. et Microb. Scandinavica. 
  3. ^ BERGER, U. (1961-01-01). "A proposed new genus of gram-negative cocci: Gemella". International Bulletin of Bacteriological Nomenclature and Taxonomy. 11 (1): 17–19. doi:10.1099/0096266x-11-1-17. 
  4. ^ "gemellus - Wiktionary". Retrieved 2015-10-31. 
  5. ^ Stackebrandt, E., B. Wittek, E. Seewaldt, and K. H. Schleifer (1982). "Physiological, biochemical and phylogenetic studies on Gemella haemolysans". FEMS Microbiology Letters. 13 (4): 361–365. doi:10.1111/j.1574-6968.1982.tb08288.x. 
  6. ^ Carmody, Lisa A.; Zhao, Jiangchao; Schloss, Patrick D.; Petrosino, Joseph F.; Murray, Susan; Young, Vincent B.; Li, Jun Z.; LiPuma, John J. (2013-06-01). "Changes in Cystic Fibrosis Airway Microbiota at Pulmonary Exacerbation". Annals of the American Thoracic Society. 10 (3): 179–187. doi:10.1513/AnnalsATS.201211-107OC. ISSN 2329-6933. PMC 3960905Freely accessible. PMID 23802813. 
  7. ^ Mosquera, J.D.; Zabalza, M.; Laniero, M.; Blanco, J.R. "Endocarditis due to Gemella haemolysans in a patient with hemochromatosis". Clinical Microbiology and Infection. 6 (10): 566–568. doi:10.1046/j.1469-0691.2000.00136.x.