Effect of Lactobacillus plantarum bacteriocin on gram-negative rods.

The antibacterial effect of bacteriocins synthesized by Lactobacillus plantarum isolated from fermented carrot juice on Enterobacteriaceae rods coming from food was studied in the experiment. Their antibacterial activity was determined employing the diffusion method, well technique. The results show that the bacteriocins examined were characterized by a different effect on test strains whose development was inhibited at the activity level from 256AU/ml to 4AU/mL.

Use of lactic and propionic acid bacteria in the production of fermented parsley juice.

Taking into consideration the proliferation rate of Propionibacterium sp. cells, pH changes and sensory properties of the fermented product obtained, selection of propionic acid bacteria (PAB) was made in order to determine their usefulness for the production of fermented parsley juice. The analysis included 12 strains, belonging to the following species: P. thoenii (4 strains), P. jensenii (6 strains), P. freudenreichii (1 strain) and P. acidipropionici (1 strain). The experiments show that many strains of propionic acid rods develop well in parsley juice, allowing to achieve the desired taste qualities of the product. The Propionibacterium strains selected by elimination were used as components of vaccine containing: Lactobacillus plantarum, Lactococcus lactis ssp. lactis, Saccharomyces cerevisiae.

Effect of high pressure on the survival rate and antibacterial activity of Bifidobacterium strains.

The effect of pressures of 1000, 700 and 400 MPa/15 min on the survival rate of Bifidobacterium infantis 1/1 was studied. 24 h milk cultures, Garsch cultures, and yogurt--to which centrifuged cell biomass of these bacteria was introduced--were subjected to pressurization. It was found that a pressure of 1000 MPa inactivated populations from 10(7) to 10(9) cfu/ml in all the environments examined. Only tens of cells in milk cultures survived a pressure of 700 MPa. Populations reduced by 4 or 5 log, depending on the environment, survived a pressure of 400 MPa. The greatest number of cells died in yogurt, where population reduction was 5 log. Bifidobacterium infantis 1/1 in milk cultures produced antibacterial metabolites active towards 89% of pathogenic bacteria strains: Enterobacteriaceae rods and species S. aureus, L. monocytogenes, B. cereus. Garsch cultures inhibited the growth of 67% of the same test strains. The antibacterial effect of experimental yogurt was much weaker than that of cultures, but it inhibited the growth of a higher number of test strains than control yogurt. Culture and yogurt pressurization with 700 MPa caused inactivation of antibacterial metabolites in all the environments.

Effect of Propionibacterium acidipropionici on the growth of Yersinia enterocolitica.

The antibacterial effect of Propionibacterium acidipropionici culture on a whey medium was determined in preparations subjected to cell inactivation with UV radiation and chloroform treatment; in concentrated biomass, centrifuged and suspended in sterile water; in a preparation subjected to cell inactivation with chloroform. The test strain was Yersinia enterocolitica 8. The preparations and culture were added, as biopreservatives, to broth media where the test strain was cultured, checking periodically the population development. It was found that a whey culture of P. acidipropionici was characterized by antibacterial activity of 64 AU/ml, but after cell inactivation this activity decreased to 16 and 8 AU/ml, depending on the method employed. The activity of concentrated biomass of live cells was at a level of 128 AU/ml, and after inactivation with chloroform--8 AU/ml. An addition of biopreservatives to the growth medium caused inhibition of test strain proliferation. Its degree depended on the antibacterial activity of the environment and population size. In the environment with activity of 42.7 AU/ml the strain Y. enterocolitica 8 whose population was hundreds of cells per ml died after 8 hours of incubation. A larger population, i.e. 10(5) cfu/ml, survived under these conditions, but did not proliferate during 24 hours of culturing.