A taxonomic study of Acinetobacter and related genera.

Summary:A computer survey was made to find the relationships of 120 strains of Gram-negative or Gram-variable non-motile coccoid rods, isolated by the author and formerly called Achromobacter. They were compared with 75 named strains of various Gram-negaiive genera, on the basis of morphological properties and biochemical tests. A recently developed similarity coefficient was used and strainswere sorted into phenons by single linkage. Most of the strains were grouped at 72·5% similarity into one large phenon. Strains outside this phenon were: Pseudomonas aeruginosa (2), P. fluorexens (3), P. saccharophila (I), P. putrefaciens (I), Escherichia coli (I), Celliiloinonas biazotiea (I), Arthrobacter globiforme (I). These were differentiated from the 72·5-phenon by various combinations of the following characters which were nearly always negative for strains within the phenon: fermentative metabolism of sugars, pigmentation, production of reducing compounds from gluconate, alkalinity from arginine, hydrolysis of starch or proteins. Within the 72·5-phenon, five smaller phenons were distinguished, most of them grouped at 82·5% similarity. The strains in each of these phenons and the characters possessed by a majority of strains and useful for the differentiation of these phenons were: Phenons I and 5 were Gram-negativemotile rods, usually peritrichous. Phenon I: Agrobacterium sp. (2), Achronzobacter hartlebii (I), Agr. tume- faciens (I). Acid was produced oxidatively from glycerol, sucrose, fructose, lactose, arabinose, xylose, galactose and glucose; H2S produced in Kligler medium; the Kovacs oxidase test positive; nitrate reduced; growth on Simmons medium and on Paton medium; no growth on digest agar at 0° or 37°; not sensitive to 2·5 i.u. of penicillin. Phenon 5: Alcaligenes faecalis (3), A. viscosus (I), A . denitrijicans (I), A . bookeri (I), Alcaligenes sp. (2). Acid not produced from sugars; oxidase-positive; nitrate reduced; growth on Simmons medium; no growth on Paton medium; growth on digest agar at 37° but not at 0°; litmus milk became alkaline; not sensitive to 2·5 i.u. of penicillin. Phenons 2, 3 and 4 were Gram-negative coccoid rods, cocci or short sods, often in pairs. Phenon 2: Bacterium (or Acinetobacter or Achromobacter) anitratuni (10), Achrornobacter lacticum (2), Herellea sp. (8), Diplococcus mucosus (61, Moraxella lwoffi (I), MJT isolate (I). Acid not produced from glycerol, sucrose or fructose; oxidative acid production from lactose, arabinose, xylose, galactose and glucose; oxidase-negative; nitrate not reduced; growth on Simmons medium and on Paton medium; growth on digest agar at 37° but not at 0°; litmus milk became acid; not sensitive to 2°5 i.u. of penicillin. Phenon 3: Achromobacter sp. (I), MJT isolates (22). Acid not produced from glycerol, sucrose or fructose; oxidative acid production from lactose, arabinose, xylose, galactose and glucose; oxidase-positive; nitrate reduced; no growth on Simmons or Paton media; growth on digest 0° at oc but not at 37°; no pH change in litmus milk; sensitive to 2°5 i.u. of penicillin. Phenon 4: Mima spp. (7), Achrornobacter venenosum (I), Alccrligenes viscosus (2), MoraxeIla lwoffi(4), Achromobacter sp. (2), Neisseriu caiarrhalis (I), MJT isolates (93). Acid not produced from sugars; no growth on Simmons medium; growth on digest agar at 0° but not at 37°; no pH change in Iitnius milk; sensitive to 2°5 i.u. of penicillin. Other characters variable. Phenons 4i, 4ii, 4iii: small phenons grouped at about 92°5:% similaritywithin Phenon 4. In properties other than sugar oxidation, Phenon 4i resembled Phenon 3, and Phenons 4ii and 4iii resembled Phenon 2, but not so closely. The minimum inhibitory concentration of penicillin was estimated for selected strains of Phenons 2, 3 and 3, and varied from 100 i.u./ ml. Strains of Phenons 3 and 4i were very sensitive, those of Phenons 2 and 4iii were resistant, and those of 4ii were intermediate or resistant.Ungrouped strains of Phenon 4 varied from very sensitive to resistant. It was concluded, on the basis of these results and the data of Mandel & Thornley (1967) on DNA composition, that the non-motile coccoid rods in Phenons 2, 3 and 4 should be placed in a separate genus from other strains in the survey. Acinetobacter Brisou & Prevot is the most suitable generic name, and strains in Phenon 2 correspond to the type species, Acinerobacter anitratus. The relationships of Phenon 3 and the sub-divisions of Phenon 4 need further study, and it is not suggested that they should be given specific rank at present. Phenons 2, 3 and 4 included strains formerly called Alcaligenes viscosus and Achromobacter; their classificition as Acinetobacter entails division of the genera Alcaligenes and Achromobacter. The genus Alcaligenes should be retained for strains resembling the motile, peritrichously flagellate type species, A. faecalis, represented in this study in Phenon 5. It is suggested that the genus Achromobacter also should be reserved for any motile peritrichous strains which may prove suitable for inclusion. The few strains in this survey which had these properties were not very similar to each other, and the borderline between these strains and Agrobacterium was not cfear. The strain ATCC I 5716, proposed as representative of the type species Acaromobacter liquefaciens (Tulecke et al. 1965) was unlike all other strains in the survey; ATCC 15716 fermented sugars and contained a large proportion of Gram-positive cells, and may be closer to a Gram-positive genus than to those studied here.