Search

Aims: To determine if nisin F has an effect on the bacterial population in the gastro-intestinal tract. Methods and Results: Six male C57BL/6 mice were intraperitoneally injected with 200 μl sterile saline and six with nisin F (200 μl, equivalent to 640 arbitrary units). Fecal samples were collected before injection and 8, 24 and 48 h after injection, and the bacteria amplified by PCR-DGGE using 16S rDNA primers. The composition of the bacterial population in the gastro-intestinal tract (GIT) of mice that were injected with saline changed during 48 h, whereas the bacterial population in the GIT remained relatively unchanged in animals injected with nisin F. Conclusions: These results suggest that nisin F inhibits the growth of specific bacteria in the GIT within the first 4 h. Furthermore, the species remained repressed for at least 44 h after one intraperitoneal injection with nisin F. Significance and Impact of the Study: This is the first report suggesting that nisin F may have a stabilizing effect on the bacterial population in the gastro-intestinal tract.

Aims: To investigate hydrogen peroxide production by lactic acid bacteria (LAB) and to determine the key factors involved. Methods and Results: Six strains of Weissella cibaria produced large amounts (2·2–3·2 mmol l−1) of hydrogen peroxide in GYP broth supplemented with sodium acetate, but very low accumulations in glucose yeast peptone broth without sodium acetate. Increased production of hydrogen peroxide was also recorded when strains of W. cibaria were cultured in the presence of potassium acetate, sodium isocitrate and sodium citrate. Oxidases and peroxidases were not detected, or were present at low levels in W. cibaria. However, strong nicotinamide adenine dinucleotide (NADH) oxidase activity was recorded, suggesting that the enzyme plays a key role in production of hydrogen peroxide by W. cibaria. Conclusions: Weissella cibaria produces large quantities of hydrogen peroxide in aerated cultures, in a process that is dependent on the presence of acetate in the culture medium. NADH oxidase is likely the key enzyme in this process. Significance and Impact of the Study: This is the first study showing that sodium acetate, normally present in culture media of LAB, is a key factor for hydrogen peroxide production by W. cibaria. The exact mechanisms involved are not known.

Aims: To identify Lactococcus garvieae isolates from radish and broccoli sprouts and compare them with virulent and less virulent mutant strains obtained from yellowtails with regard to KG phenotype, presence of a capsule and virulence towards yellowtails and mice. Methods and Results: Comparative 16S rRNA gene sequence analysis of six isolates obtained from radish and broccoli sprouts indicated that they were L. garvieae (similarity >99%). They were compared with KG9502, Lg2 and ATCC49156 strains obtained from yellowtails. A less virulent mutant strain Lg2-S was obtained by Lg2 subculture. Biochemical characterization of the six strains resembled that of KG9502, Lg2, ATCC49156 and Lg2-S, except for saccharose and tagatose acidification and the presence of hippuricase. These six strains were nonpathogenic towards yellowtails and mice, nonsusceptible to bacteriophages and demonstrated heterogeneity on pulsed-field gel electrophoresis analysis. Using transmission electron microscopy, a capsule was observed in KG9502 and Lg2 but not in ATCC49156 and Lg2-S. Conclusions: We isolated L. garvieae strains that lacked pathogenicity towards yellowtails and mice from radish and broccoli sprouts; these were noncapsulated and exhibited KG+ phenotype. Significance and Impact of the Study: This is the first documentation of L. garvieae isolated from terrestrial plants. These isolates exhibited genetic diversity; however, they were noncapsulated and nonpathogenic towards yellowtails and mice.

Aims: To investigate the microbial community in sunki, an indigenous, unsalted, fermented vegetable, made from the leaves of red beet. Methods and Results: Fermenting samples were collected at 1- to 2-day intervals from four houses and investigated by culture-dependent and culture-independent techniques. PCR-Denaturing-Gradient-Gel-Electrophoresis profiles indicated that the bacterial community was stable and Lactobacillus delbrueckii, Lact. fermentum and Lact. plantarum were dominant during the fermentation. This result agreed well with that obtained by the culturing technique. Moulds, yeasts or bacteria other than lactic acid bacteria (LAB) were not detected. Conclusions: The bacterial community was stable throughout the fermentation, and Lact. delbrueckii, Lact. fermentum and Lact. plantarum were dominant. The acidic pH and lactic acid produced by LAB probably preserve the sunki from spoilage. Significance and Impact of the Study: This is the first report on the use of both culture-dependent and culture-independent techniques to study the bacterial community in sunki. A combination of culture-dependent and culture-independent techniques is necessary for the analysis of complex microbial communities.