Long or short rods or cocci which divide like rods in one plane only, producing chains, occasionally tetrads; filamentous as well as so-called false branching forms sometimes occur. Usually non-motile but may be motile, the motile species possessing peritrichous flagella. Gram-positive. Pigment production is rare; a few species produce a yellow, orange, red or rusty brown pigment. Gelatin liquefaction is rare among the microaerophilic species but is more common among the strict anaerobes. Surface growth on all media is poor or absent. Carbohydrates are essential for good development; they are fermented to lactic acid, sometimes with volatile acids, alcohol and carbon dioxide as by-products. Nitrites not produced from nitrates, but among the strict anaerobes there are a few species that are known to reduce nitrates and some that have not been tested for nitrate reduction. Micro- aerophilic to anaerobic. Found regularly in the mouth and intestinal tract of man and other animals, in food and dairy products and in fermenting vegetable juices; a few species are highly pathogenic. Key to the tribes of family Lactobacillaceae. I. Cocci occurring singly, in pairs and in chains (rarely tetrads). Tribe I. Streptococceae, p. 506. II. Rods, occurring singly, in pairs and in chains. Individual cells may be very long or even filamentous. Tribe II. Lactobacilleae, p. 541. TRIBE I. STREPTOCOCCEAE TREVISAN, 1889. (I generi e le specie delle Batteriacee, 1889, 29.) Cells spherical or elongate, dividing in one plane only, usually occurring in pairs or in chains. Gelatin is rarely liquefied. None of the species grows abundantly on solid media. The microaerophilic species attack carbohydrates and polyhydro.xy alcohols, producing lactic acid by homofermentation or lactic and acetic acids, alcohol and carbon dioxide by heterofermentation; the strictly anaerobic species attack protein decomposition products, organic acids and usually carbohydrates with the production of carbon dioxide, hydrogen and other products. Microaerophilic to anaerobic. Catalase-negative. May or may not be pathogenic; some pathogenic species grow poorly without blood serum or other enrich- ment fluids. Found in various lesions and in the normal mouths and intestines of man and other animals, in food and dairy products and in fermenting plant juices. Key to the genera of tribe Streptococceae. I. Facultatively anaerobic to microaerophilic. A. Homofermentative, producing only traces of end-products other than lactic acid from carbohydrates. 1. Produce dextro rotatory lactic acid from glucose. a. Parasites which grow poorly on artificial media. Cells usually in pairs, often elongated. Bile-soluble. Genus I. Diplococcus , p. 507. aa. Parasites and saprophytes. Normally form short or long chains. Not soluble in bile solutions. Genus II. Streptococcus, p. 508. 2. Produces a racemic mixture of lactic acid from glucose. Occurs singly, as tetrads, pairs or even short chains. Genus III. Pediococcus, p. 529.
