GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

14. TYPES OF FERMENTATION

14.3. LACTIC ACID FERMENTATION AND THE FAMILY LACTOBACILLACEAE

14.3.1. Characteristics of lactic acid bacteria

Lactic acid Bacteria are grouped into the family Lactobacillaceae. This group is morphologically heterogeneous, but shares common physiological traits. All of these bacteria are Gram-positive, non-spore-forming (with the exception of Sporolactobacillus inulinus), and predominantly non-motile. They all utilize CARBOHYDRATES as a source of carbon and energy, producing lactic acid as a byproduct. Unlike enterobacteria, which also produce lactate, lactic acid bacteria are capable exclusively of Fermentation and lack Hemoproteins (Cytochromes and catalase). Nevertheless, members of the family Lactobacillaceae can grow in the presence of oxygen, remaining aerotolerant.

Another distinctive feature of lactic acid bacteria is their requirement for growth factors. The growth of most of these bacteria necessitates a range of Vitamins (thiamine, pantothenic acid, nicotinic acid, Folic acid, biotin), Amino Acids, as well as Purines and Pyrimidines. Lactic acid bacteria are typically cultivated on complex media containing sufficiently high concentrations of Yeast autolysate, tomato juice, whey, and even Blood. Consequently, lactic acid bacteria are unique "metabolic cripples" that presumably lost The ability to synthesize many metabolites due to their specialization (growing in milk and other nutrient-rich environments). On the other hand, they possess an ability absent in many other microorganisms: the utilization of milk sugar (lactose). Lactose is found exclusively in mammals and is absent in the plant kingdom. It is a disaccharide that must be cleaved into glucose and galactose prior to Catabolism (via the enzyme β-galactosidase). Because lactic acid bacteria produce large amounts of lactic acid, their cultivation medium must be buffered.

Lactic acid bacteria are never found in soil or bodies of Water. Their natural habitats include:

milk and milk-Processing environments, dairy products (Lactobacillus lactis, L. bulgaricus, L. casei_r L. fermentum, L. brevis, Streptococcus lactis); plants and plant residues (Lactobacillus plantarum, L. delbrueckii, L. fermentum, L. brevis, Streptococcus lactis, Leuconostoc mesenteroides);

the intestines and mucous membranes of humans and animals (Lactobacillus acidophilus, Bifidobacterium bifidum, Streptococcus faecalis, S. bovis, S. pneumoniae).

Among streptococci, there are blood parasites that act as highly virulent pathogens.

Depending on the products formed during glucose fermentation (lactic acid exclusively, or accompanied by other organic products and CO₂), lactic acid bacteria are divided into homo- and heterofermentative types.