**2. Microbiology**

Nutritionally variant streptococci were first described by Frenkel and Hirsch in 1961 from blood cultures of cases of subacute bacterial endocarditis and from otitis media. These cell wall deficient, L form 'streptococci' were noted to grow in satellite colonies around other bacteria requiring substances secreted by other bacteria for growth [1]. 'Abiotrophia' means life nutrition deficiency, referring to the need of specific nutrients in media for growth of these bacteria [26]. They are catalase-negative, oxidase-negative, facultative anaerobic gram positive bacteria [27]. They often form white-gray, non-hemolytic colonies. These organisms hardly grow in culture media that streptococci ordinarily grow, such as sheep blood agar. They require supplementation of L-cysteine or pyridoxal HCl. In the absence of these supplements, NVS can also grow forming satellite colonies adjacent to streaks of helper bacteria such as *Staphylococcus aureus* or *Staphylococcus epidermidis*.

Bouvet et al. in 1989 showed that NVS could be divided into two groups, *Streptococcus defectivus* and *Streptococcus adiacens* by DNA–DNA hybridization studies. They noted that there was less than 10% DNA homology with the reference streptococcus species [28].

In 1995, Kawamura et al. proposed that these distinct species be transferred to a new genus, *Abiotrophia*, as *Abiotrophia adiacens* and *Abiotrophia defectiva* by using 16S rRNA gene sequencing. Subsequently two new species were added to this genus; *Abiotrophia elegans* [29] isolated from a patient with endocarditis and *Abiotrophia balaenopterae* [30] from a minke whale (*Balaenoptera acutorostrata*).

Finally, in 2000, Collins et al. proposed the taxonomy of NVS that we use today. They pointed out that genus *Abiotrophia* consisted of two distinct lines. *Abiotrophia defectiva* and a robust group consisting of *A. adiacens*, *A. balaenopterae* and *A. elegans*. They reclassified *A. adiacens, A. balaenopterae* and *A. elegans* into genus *Granulicatella* (*small chain of small grains in Latin*) and *Abiotrophia defectiva* into genus *Abiotrophia* [27]. Shortly before this taxonomy revision, Kanamoto et al. proposed a new strain, *Abiotrophia para-adiacens*, related to *Granulicatella adiacens* which is rarely reported but not widely published [31, 32].
