Lactic acid bacteria antibiotic production

Lactic Acid B cteri. The lactic acid bacteria are ubiquitous in nature from plant surfaces to gastrointestinal tracts of many animals. These gram-positive facultative anaerobes convert carbohydrates (qv) to lactic acid and are used extensively in the food industry, for example, for the production of yogurt, cheese, sour dough bread, etc. The sour aromatic flavor imparted upon fermentation appears to be a desirable food trait. In addition, certain species produce a variety of antibiotics. 

Modern methods of livestock production are intensive and the environmental conditions stress the animals. The use of antibiotics promotes growth and protects the animals from otherwise certain infection under these conditions. Antibiotic-like compounds formed in lactic acid fermentations prevent proliferation of spoilage and pathogenic microorganisms and increase the shelf life of the products. Nisin is a antimicrobial produced by a lactic acid bacterium and is used in some countries as a food preservative. Some lactic acid bacteria are capable of favorably influencing the fecal flora in man and animals. 

The mechanism(s) by which lactic acid bacteria inhibit or inactivate other bacteria is not totally clear. Daly et al. (1972), Speck (1972), and Gilliland and Speck (1972) have cited evidence which suggests that the following may be involved (1) production of antibiotics such as nisin, diplococcin, acidophilin, lactocidin, lactolin, and perhaps others (2) production of hydrogen peroxide by some lactic acid bacteria (3) depletion of nutrients by lactic acid bacteria, which makes growth of pathogens difficult or impossible (4) production of volatile acids (5) production of acid and reduction in pH (6) production of D-leucine and (7) lowering the oxidation-reduction potential of the substrate. 

Shortly after their development in the 1940s, antibiotics were used in veterinary medicine, first to prevent or treat mastitis in cows and later for the treatment of other diseases. Initial concern about antibiotic residues in milk was not a public health issue but came from dairy processors who noticed inhibition of starter cultures used in the production of cheese and yogurt, thus generating a need for screening tests to examine milk for antibiotic residues. " Since inhibition of starter cultures by penicillin in milk was the main problem, the earliest microbial inhibition assays were based on growth inhibition of lactic acid bacteria. Spores of Bacillus species were also utilized spores are easier to handle and far more stable than the vegetative cells. 

The lipolytic activity of propionibacteria was shown to be higher than that of lactic acid bacteria (Depuis et al., 1993). Propionibacterial lipids apparently are not only structural components of the cell, but may also have a protective role against the action of some antibiotics. In the presence of polymyxin M (Konovalova, 1970) the production of lipids and phospholipids was increased (Fig. 4.15). 

Pore-Forming Toxins (Proteins and Peptides TC l.C.) represent a group of proteins that have considerably expanded over the last few years within the lactic acid bacteria group (Table 4.2). The production of bacteriocins is a very desirable trait with biotechnological applications. Bacteriocins are bacterially produced peptide antibiotics with the ability to kill a limited range of bacteria, usually but not always those that are closely related to the producer bacterium. 

Birri, D.J., Brede, D.A., Tessema, G.T., and Nes, I.F. (2013). Bacteriocin production, antibiotic susceptibility and prevalence of haemolytic and gelatinase activity in faecal lactic acid bacteria isolated from healthy Ethiopian infants. Microl) coZ 65, 504-516. 

Lactic acid-producing bacteria associated with fermented dairy products have been found to produce antibiotic-like compounds caUed bacteriocins. Concentrations of these natural antibiotics can be added to refrigerated foods in the form of an extract of the fermentation process to help prevent microbial spoilage. Other natural antibiotics are produced by Penicillium wqueforti the mold associated with Roquefort and blue cheese, and by Propionibacterium sp., which produce propionic acid and are associated with Swiss-type cheeses (3). 

Fermentation. Fermentation is defined (Ref 3) as the production of chemicals by a series of enzyme catalyzed reactions with bacteria, yeasts, or molds under aerobic or anaerobic conditions. At present, fermentation is used to produce complex molecules not easily synthesized such as penicillin and other antibiotics, vitamin BI2, and enzymes. Formerly, glycerine (See Fetmentol), acetone, butanol, and citric lactic acids were some of the chemicals produced by fermentation process. Synthesis is now a more economical route to these materials (See also Refs 1 2) Refs 1) P.A. Wells G.E. Ward, IEC 31, 172-77(1939) 2) H.E. Silcox S.B. Lee,... 

Industrial applications of fermentation include the production of alcohol and glycerol from yeast, lactic acid, acetone, and butyl alcohol from various bacteria, and citric acid, antibiotics, and vitamins from mould fermentations. 

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