Reference Work Entry

The Prokaryotes

pp 511-518

The Genus Gemella

  • Matthew D. Collins

Introduction

The genus Gemella until recently consisted of two species, G. haemolysans (the type species of the genus), and G. morbillorum (Berger, 1992). In the past few years four other species, G. bergeri (Collins et al., 1998b), G. sanguinis (Collins et al., 1998a), G. palaticanis (Collins et al., 1999) and G. cuniculi (Hoyles et al., 2000), have been assigned to the genus. The cells of gemellae are cocci, which are arranged in pairs, tetrads, small irregular clusters and sometimes in small chains; elongate and rod-shaped forms may also occur. Cells stain Gram positive but often decolorize easily and appear Gram negative. The organisms are facultatively anaerobic, preferring an atmosphere rich in CO2, but growth can occur under both aerobic and anaerobic conditions (Berger, 1992). Gemellae are nonmotile and do not form endospores. They are cytochrome oxidase- and catalase-negative.

The genus Gemella was originally monospecific, containing only G. haemolysans. Because the organism was ...

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