A Gemella species was first described as Neisseria hemolysans in 1938. It was reclassified as a new genus in 1960 when strains were found to be distinct enough from Neisseria to require a new genus. The name was suggested based on the organism being a diplococcus and gemellus is the diminutive of geminus, 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.