FAMILY X. LACTOBACILLACEAE 509 



than 1 millimeter in diameter. Colony variants within one species may range from rough 

 to smooth (matt to glossy) to mucoid. Subsurface colonies are usually lenticular. Carbohy- 

 drate fermentation is homofermentative with dextro rotatory lactic acid as the dominant 

 end-product. Carbon dioxide is produced in very small quantities or not at all from sugar 

 fermentation. Ethanol, acetic acid and formic acid may be produced in appreciable quanti- 

 ties from glucose if allowed to ferment in alkaline media (Gunsalus and Niven, Jour. Biol. 

 Chem., 1I^5, 1942, 131). Many of the streptococci oxidize a number of the alcohols, glycols 

 and short-chain fatty acids (Gunsalus and Wood, Jour. Bact., 44, 1942, 523; Gunsalus and 

 Umbreit, Jour. Bact., 49, 1945, 347; Niven, Evans and White, Jour. Bact., ^9, 1945, 105; 

 Wolin, Evans and Niven, Jour. Bact., 6^, 1952, 531), but the energy derived from these 

 respiratory mechanisms is not utilized directly for growth. However, some enterococcus 

 cultures may show moderately superior growth under aerobic conditions (Seeley and Van- 

 Demark, Jour. Bact., 61, 1951, 27). The cytochrome systems are absent; catalase-negative. 

 Do not reduce nitrate to nitrite. Facultative with respect to oxygen. Not soluble in ten per 

 cent bile. Proteolytic strains found only in the enterococcus group. All streptococci are 

 fastidious with respect to their nutritional requirements, thereby requiring a number of 

 the B vitamins and amino acids for growth. The nutritional requirements are, in general, 

 species specific, but some variations may be noted within one species. Some strains require 

 an unsaturated fatty acid or increased carbon dioxide tension for growth. In some in- 

 stances, the nutritional requirements may be of aid in the identification of a species. The 

 reader is referred to Dubos (Bacterial and Mycotic Infections of Man. Lippincott, 1948, 

 240) for a general summary of the nutritional requirements for most of the species. Sero- 

 logical tests, specifically the Lancefield precipitin technique, have proved to be of distinct 

 value in classifjang the streptococci. In general, all streptococci except those in the viridans 

 group possess a serologically active, group specific "C" substance (polysaccharide), thus 

 allowing them to be placed into serological groups by the precipitin technique. One sero- 

 logical group may comprise more than one species. Also, one serological group may possess 

 a number of established serological types based upon the presence of capsular type-specific 

 antigens and detected by the agglutinin or precipitin technique. Thus far, little relationship 

 has been noted between serological type specificity and species specificity as established by 

 their respective physiological characteristics. Several instances are known in which certain 

 strains of streptococci possess common type antigens but belong to different serological 

 groups. Members of the viridans group possess demonstrable type antigens but, for the 

 most part, they have been of little taxonomic value. The streptococci are commonly found 

 wherever organic matter containing sugars is accumulated. They occur regularly in the 

 mouth and intestine of man and other animals, in dairy and other food products and in 

 fermenting plant juices. Some species are pathogenic. 



The arrangement of the species presented is in harmony with the suggestions of Sherman 

 (Bact. Rev., 1, 1937, 3) in which the facultative streptococci are separated into four general 

 groups: the pyogenic, the viridans, the enterococcus and the lactic groups. The arrange- 

 ment of the species into these four categories was based upon a series of common physio- 

 logical characteristics possessed by the respective groups, the most important of which was 

 their temperature limits for growth. However, as new species are recognized, the indi- 

 viduality of each group naturally becomes less distinct, and the difficulties of placing the 

 new species, which may possess characteristics of more than one group, are increased. For 

 example. Streptococcus tiberis Diernhofer, a member of the viridans group, possesses certain 

 characteristics that would tempt one to place it in the enterococcus group, while Strepto- 

 coccus acidominimus Ayers and Mudge, also a member of the viridans group, might be 

 considered a member of the pyogenic group. 



The type species is Streptococcus pyogenes Rosenbach. 



It is difficult to draw up a workable key for streptococci. Keys, of necessity, emphasize 

 single characters or, at most, only a few characters, and these are not necessarily the most 



