I. Ivanova

Characterization of a bacteriocin produced by Streptococcus thermophilus 81.

A new bacteriocin, produced by Streptococcus thermophilus 81 has been isolated, purified and characterized. By its heat sensitivity and broad inhibitory spectrum it does not resemble any other S. thermophilus bacteriocin. The mode of action is bacteriostatic. This peptide of 32 amino acids is efficient against several Bacillus species, Listeria monocytogenes, Salmonella typhimurium, Escherichia coli, Yersinia pseudotuberculosis and Yersinia enterocolitica. This bacteriocin is heat labile but its activity was not altered by pH variation from 3 to 10. Six months of storage at 40 degrees C did not influence the activity. The inactivation by detergents and the inability to resolve the protein in SDS-PAGE supposes a more complex structure or a possible stabilizing effect of other molecules. The low sensitivity of Lactobacillus delbrueckii subsp. bulgaricus to the isolated bacteriocin suggests that S. thermophilus 81 may be used in yoghurt starters.

Detection and characterization of a novel antibacterial substance produced by Lactobacillus plantarum ST 31 isolated from sourdough.

Lactobacillus plantarum ST31 isolated from sourdough produced an antimicrobial substance inhibiting other strains of the genera Lactobacillus, Leuconostoc, Pediococcus, Streptococcus, Bacillus and some foodborne pathogens including Staphylococcus aureus. This antimicrobial substance was inactivated by proteolytic enzymes. Consequently, it was characterized as a bacteriocin and was designated plantaricin ST31. This bacteriocin was stable in the pH range 3-8 and it was not affected by amylolytic enzymes. Production of plantaricin was pH and temperature dependent, and maximum yields were obtained in MRS broth cultures maintained at pH 6 and incubated at 30 degrees C in the exponential phase to the early stationary growth phase of the producer organism. This bacteriocin was purified by using consecutive ammonium sulfate and reversed-phase chromatography. It is a peptide of 20 amino acid residues with a mass of 2755+/-0.3 Da, as determined by electrospray mass spectrometry. The sequence of Plantaricin ST31 showed no similarity to those of other bacteriocins. Plantaricin ST31 production appeared to be chromosomally encoded.

Isolation and partial biochemical characterization of a proteinaceous anti-bacteria and anti-yeast compound produced by Lactobacillus paracasei subsp. paracasei strain M3.

New proteinaceous active substance produced by Lactobacillus paracasei subsp. paracasei strain M3 used as a starter for Bulgarian yellow cheese was identified and studied. It displayed bactericidal and fungistatic activities. Its activity was checked against over 60 bacterial and yeast strains. It was efficient against Bacillus subtilis ATCC 6633, several L. delbrueckii species, Helicobacter pylori NCIPD 230 and some yeast species, for example Candida albicans, C. pseudointermedia NBIMCC 1532, C. blankii NBIMCC 85 and Saccharomyces cerevisiae NBIMCC 1812. The synthesis of the substance by producing strain was detected in the late logarithmic growth phase during batch fermentation. Anion exchange chromatography, reversed phase chromatography (RPC) on C4 column and HPLC on C18 column were used for partial purification of this antimicrobial compound. The gene responsible for the synthesis of the active substance is located on the bacterial chromosome.

Influence of Growth Medium on Bacteriocin Production in Lactobacillus Plantarum ST31

Introduction The reported antimicrobial potentialites of lactic acid bacteria are of great interest in the development starter cultures for food fermentation (33). Such inhibitory abilities of starter cultures have a preferential selection in food manufacture for the biological control of food-borne pathogens with regularly and healthy agencies at the same time without restoring to more severe physical treatment of the food (15, 23, 24, 27, 28, 31). The antimicrobial properties are mainly based on acid production, competition for nutrients and space, formation of hydrogen peroxide, C02, diacetile and other products of catabolism, and bacteriocins (30). Bacteriocins are proteinaceouse compounds produced by bacteria that exhibit a bactericidal or bacteriostatic mode of action against sensitive bacterial species (21). Bacteriocin producing strains of L. plantarum were reported from many foods including meat and meat products (12, 32), milk (29), cheese (14), fermented cucumber (2, 7), olives (17), fermented cereal doughs (13, 16), silage (4), pineapple (19), grapefrruit juice (20). Some bacteriocin from L. plantarum were isolated and partially characterised (1, 14, 17, 19, 20, 25). A variety of these bacteriocins have been reported to inhibit spoilage bacteria and foodborne pathogens. There is an increasing interest for lactic acid bacteria isolated from fermented bread dough (sourdough). A bacteriocinic activity was shown for strains of L. sanfranciso (6), L. bavaricus (22) and L. reuteri (11). This

Detection and characterization of a novel antibacterial substance produced by a Lactobacillus delbrueckii strain 1043

A novel antibacterial substance produced by a strain isolated from Bulgarian yellow cheese was characterized. The producer strain was identified by molecular typing to belong to the species Lactobacillus delbrueckii, which is a rare producer of bacteriocins. The inhibitory agent was heat stable and active against lactic acid bacteria species and several food‐borne pathogens : Listeria monocytogenes, Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Yersinia enterocolitica and Y. pseudotuberculosis. Its sensitivity to amylolitic enzymes and lipase suggested that a lipid and carbohydrate moiety could be important for the activity. The amino acid content of the purified bacteriocin was estimated to 29 amino acids. The bacteriocin was shown to be small (3·6–6 kDa) by three different methods : HPLC gel‐filtration, SDS‐PAGE and amino acid contents.

Isolation, taxonomic identification and hydrogen peroxide production by Lactobacillus delbrueckii subsp. lactis T31, isolated from Mongolian yoghurt: inhibitory activity on food-borne pathogens

Aims:  The aim of this work was to isolate lactic acid bacteria (LAB) strains from Mongolian tarag (a traditionally homemade yoghurt) displaying antimicrobial activities against food‐borne pathogens, identify inhibitory substances and study the kinetics of their production.

Antibacterial Peptides from Goat and Sheep Milk Proteins

ABSTRACT Milk is an excellent source of well balanced nutrients and also exhibits a range of biological activities that influence digestion, metabolic responses to absorbed nutrients, growth and development of specific organs, and resistance to disease. Goat milk is as close to perfect food as possible in nature. Bioactive peptides have been defined as specific protein fragments that have a positive impact on body functions or conditions and may ultimately influence health. It can be generated during milk fermentation by the proteolytic activity of starter cultures. The beneficial health effects may be classified as antimicrobial, antioxidative, antithrombotic, antihypertensive and immunomodulatory. Sheep and goat milk proteins are also important sources of bioactive ACE inhibitory peptides and antihypertensive peptides. They can provide a non- immune disease defence and control of microbial infections. The activity of these biofunctional peptides is based on their inherent amino acid composition and sequence. The size of active sequences may vary from two to twenty amino acid residues. The total antibacterial effect in milk is greater than the sum of the individual contributions of immunoglobulin and nonimmunoglobulin defence proteins such as LF, LP, lysozyme, and other peptides. A variety of naturally formed bioactive peptides have been found in fermented dairy products, such as yoghurt, sour milk and cheese. BP have the potential to be used in the formulation of health-enhancing nutraceuticals, and as potent drugs with well defined pharmacological effects.

Improving safety of salami by application of bacteriocins produced by an autochthonous Lactobacillus curvatus isolate.

The aims of this study were to isolate LAB with anti-Listeria activity from salami samples, characterize the bacteriocin/s produced by selected isolates, semi-purify them and evaluate their effectiveness for the control of Listeria monocytogenes during manufacturing of salami in a pilot scale. Two isolates (differentiated by RAPD-PCR) presented activity against 22 out of 23 L. monocytogenes strains for bacteriocin MBSa2, while the bacteriocin MBSa3 inhibited all 23 strains in addition to several other Gram-positive bacteria for both antimicrobials and were identified as Lactobacillus curvatus based on 16S rRNA sequencing. A three-step purification procedure indicated that both strains produced the same two active peptides (4457.9 Da and 4360.1 Da), homlogous to sakacins P and X, respectively. Addition of the semi-purified bacteriocins produced by Lb. curvatus MBSa2 to the batter for production of salami, experimentally contaminated with L. monocytogenes (10(4)-10(5) CFU/g), caused 2 log and 1.5 log reductions in the counts of the pathogen in the product after 10 and 20 days respectively, highlighting the interest for application of these bacteriocins to improve safety of salami during its manufacture.

Investigation of Bacteriocin Activity of Lactic Acid Bacteria Isolated from Boza

ABSTRACT The contents of the microflora isolated from boza “Belgrano” has been studied. Of 80 isolated strains of lactic acid bacteria a group of 33 types showed antibacterial activity against different test microorganisms (Listeria innocua F, L. plantarum 73, L. cremoris 117, E. coli). The most prospective strains have been characterized by means of a test. The strain defined as Lactococcus lactis sbsp. lactis 14 has been isolated. Its growth curve and its ability to produce bacteriocin under different conditions of cultivation have been studied. An attempt has been made for initial purification of bacteriocin by means of a classical method.

Effect of oligosaccharides on the growth of Lactobacillus delbrueckii subsp. bulgaricus strains isolated from dairy products.

Eighteen lactic acid bacteria (LAB) strains isolated from dairy products, all identified as Lactobacillus delbrueckii subsp. bulgaricus, were tested for their ability to grow on three different oligosaccharides: fructo-oligosaccharides (FOS), gluco-oligosaccharides (GOS) and galacto-oligosaccharides (GalOS). The growth of LAB on different oligosaccharides was very different. Study of the antimicrobial activities of these LAB indicated that the system of uptake of unusual sugars influenced in a specific way the production of antimicrobial substances (bacteriocins) specific against gram-negative bacteria. The added oligosaccharides induced LAB to form end-products of a typical mixed acid fermentation. The utilization of different types of oligosaccharides may help to explain the ability of Lactobacillus strains to compete with other bacteria in the ecosystem of the human gastro-intestinal tract.