Lactic Acid Bacteria

LACTIC ACID BACTERIA, microbes that cause lactic acid fermentation in milk (and dairy products), expressed in the fermentation of milk sugar into lactic acid; due to the formation of acid, milk coagulation occurs. L. a. b. include rods and cocci. The first belong to acidophilic bacilli and possess their properties (see Bacteria, acidophilic bacilli); according to the classification of Lehmann and Neumann, the rods together with other acidophilic bacilli form the group "Plocamobacteria," and according to Heim and Schlirf, the group of acidobacteria. According to the American classification (Bergey), all L. a. bacilli form a special family—Lactobacillaceae (see Microorganisms). The most important representatives of the group are Bac. bulgaricus, Bac. caucasicus, and others. Lactobacillus bulgaricus (Grigoroff)—see Lactobacillin and Microorganisms, table. Mechnikov proposed Bac. bulgaricus for replacing the "wild" intestinal flora in humans; however, it is difficult to acclimatize in the intestine, which is why American doctors prefer for this purpose Bac. acidophilus (Moro), which develops well in the intestine (see Bacteria, acidophilic bacilli). Lactobacillus caucasicus (Beijerinck)—see Microorganisms. Bact. mazun, 2.7-21 μ in length and 1-1.1 μ in width, immobile, Gram-positive rod; does not grow on ordinary nutrient media; on agar with whey it forms colonies with an uneven edge and hair-like outgrowths into the surrounding environment. It is contained in matsun, a dairy product made in Armenia. Apparently identical with Lactobac. caucasicus. Lactobac. lactis acidi Leichmann—see Microorganisms, table. Lactobac. acidophilus (Moro)—see Bacteria, acidophilic bacilli. In addition to those listed, lactic acid bacteria include Lactobacillus Boas-Oppleri, found in gastric contents, mainly in stomach cancer; Lactobacillus helvetieus (syn. Bac. casei Freudenreich's), isolated from sour milk and cheeses (see Microorganisms, table); Lactobacillus busae asiaticus (Bact. busae asiaticae Tschekan), isolated from buza, and others. The microbe most often causing milk to sour on cold is Streptococcus acidi lactici (Grotenfeldt) or according to the American classification—Streptococcus lacticus (Lister) Lonis (see Microorganisms, table) [see also separate table (pp. 83-84), fig. 2]. To obtain the best growth of all types of lactic acid microbes, Omeliansky recommends Coanda's agar: 1 liter of milk is boiled for 5 minutes, 1.5 cm³ of hydrochloric acid is added and filtered through cloth. The resulting serum is slightly alkalized and to 1 liter is added 300 cm³ water, 3 g gelatin, 15 g peptone and 20 g agar. The mixture is heated in an autoclave, filtered and sterilized. L. a. b. have great importance in dairy farming, as they participate in the formation of various lactic acid products (simple sour milk, lactobacillin, sour cream, cottage cheese, cheeses, kefir, kumys, etc.).