Physiological and molecular techniques for the study of bacterial community development in sausage fermentation.

The development of the microbial community involved in the production process of Italian dry sausage was investigated using physiological analysis and molecular techniques for strain typing and taxonomical identification. A cycle of sausage production was followed collecting samples during the 2 months of ripening process. Microbiological analysis allowed the identification of the main bacterial groups responsible for the fermentation process as lactobacilli and coagulase-negative staphylococci. The use of a polymerase chain reaction-based technique of strain typing, RAPD fingerprinting, demonstrated that the environmental parameters interact to select a limited number of strains that dominate the fermentation process. The staphylococcal populations were characterized for their physiological properties and the two dominant strains were identified as Staphylococcus xylosus and Staph. sciuri. The use of 16S rDNA sequencing allowed the definition of the taxonomical position of the two dominant strains of lactic acid bacteria, as belonging to Lactobacillus sake and Lact. plantarum.

Protection of young chicks against Salmonella kedougou by administration of intestinal microflora.

One-day old chickens were treated with a faecal suspension and faecal samples were cultivated either in non-selective broth (Viande Levure broth) or in broths selective for Lactobacillus spp., Bacteroides spp., faecal enterococci and coliforms. The chickens were infected 48 h later with 10(4) colony-forming units of nalidixic-acid resistant Salmonella kedougou and examined seven days later. Faecal suspensions and faecal samples cultivated in non-selective broth exerted a protection against Salmonella infection; no protection was obtained with faecal samples cultivated in selective broths, administered either alone or in combination.

The effect of some antibiotics on Enterococcus faecium SF 68 inoculated in germ-free mice.

A strain of Enterococcus faecium SF 68 (sensitive to penicillin, tetracycline, virginiamicin and tylosin, but resistant to streptomycin) was administered to five groups of germ-free mice. Each group was subsequently given 40 micrograms/ml and then 80 micrograms/ml of a single antibiotic. The following determinations were made: a) colonization of the bacterial strain before and after administration of the antibiotic and b) the MICs in the original strain and after administration of the antibiotic (80 micrograms Iml). The results show that in the mice treated with streptomycin, colonization is not influenced by the antibiotic treatment; in mice treated with antibiotics to which the strain is sensitive, the colonization increases in proportion to the level of the antibiotic resistance (tylosin and tetracycline).

Serum cholesterol levels in axenic mice colonized with Enterococcus faecium and Lactobacillus acidophilus.

Hypocholesterolemic effect was shown in axenic, mono, bicolonized and conventional mice: the effect was different depending on probiotic properties of intestinal microorganisms. Contamination by Enterococcus faecium CX determined the highest effect: haematic cholesterol level decrease was 16.9% in females and 7.8% in males. In mice contaminated by Lactobacillus acidophilus N5 the decrease of haematic cholesterol levels was less and not relevant in mice contaminated by conventional microflora. Enterococcus faecium CX and Lactobacillus acidophilus N5 strains were able to grow in presence of bile salts, to colonize intestinal tract, to survive at gastric conditions and to assimilate cholesterol (E. faecium more than L. acidophilus). The authors consider the possibility to associate probiotic strains with these characteristics for the health of consumers.

Antagonism and adhesion among isogenic strains of Lactobacillus reuteri in the caecum of gnotobiotic mice.

Interactions between a wild adhesive Lactobacillus reuteri strain isolated from chicken crop and its isogenic plasmid-free derivative were studied. Antagonism between these strains was tested in vitro or associated with gnotobiotic mice. The cured strains repressed the establishment of the wild, plasmid bearing strain in the gastrointestinal tract of gnotobiotic mice. Interactions between isogenic strains were independent of the amount of cells administered to mice. The cured derivative strain maintains its specific ability to adhere to epithelial cells of chicken crop.

In vivo transfer of pAM beta 1 from Lactobacillus reuteri to Enterococcus faecalis.

Trials were conducted to determine the in vivo transferability of plasmid-mediated antibiotic resistance between two strains of enteric Gram-positive bacteria. Germ-free mice were associated with the donor Lactobacillus reuteri DSM 20016 strain, carrying the broad host range pAM beta 1 plasmid, and with the Enterococcus faecalis JH2SS recipient strain. Analysis of faecal content of associated mice demonstrated that the in vivo transfer of this plasmid did occur and that frequencies of conjugation were affected by the presence of subtherapeutic levels of antibiotic in the diet.

Study on crop adhesion genetic determinant in Lactobacillus reuteri.

The genetic determinant responsible for adherence in one strain of Lactobacillus reuteri isolated from chicken crop has been investigated. After curing experiments carried out on this strain, a plasmid-free derivative was obtained, resulting unchanged as regards adhesion ability and carbohydrate fermentation pattern, but showing a loss of antibiotic resistances. It is suggested a possible localization on chromosome of adhesion determinant.

Lactobacillus lactis as dominant lactobacilli flora in human intestine.

The presence of Lactobacillus lactis, as a dominant lactic acid microflora, has been demonstrated in human feces by means of phenotypic and genotypic tests. This unusual fecal bacteria allows some considerations on the ubiquity and environmental specificity of the lactobacilli.

Colonization of a human intestine by four different genotypes of Lactobacillus acidophilus.

To understand the effect on a human host suffering from intestinal disorders we supplied non fat milk cultures of Lactobacillus acidophilus for 25 days. The picture of the faeces bacterial count was completely different before and after treatment and we noticed increases in lactobacilli, bifidobacteria and coliforms while the clostridia decreased. The lactobacilli treatment solved the diarrohea problem. Of the four genetic lines of L. acidophilus supplied only D179, isolated from calf faeces, and ATCC 4356 of human origin were found able to colonize the intestine of the little girl, while 255S isolated from swine and D328 isolated from calf faeces, did not find favourable growth conditions.

Genetic heterogeneity among Lactobacillus acidophilus strains.

Physiological characteristics, DNA base composition (% GC) and DNA-DNA reassociation values were determined for 138 Lactobacillus acidophilus strains. Twenty seven strains were received from various culture collections and 111 strains were freshly isolated during a study on the composition of the intestinal lactic microflora of piglets and suckling calves. All strains had physiological characteristics which were substantially similar. The strains isolated from pigs were unable to ferment trehalose. The % GC ranged from 35.8 to 43.4. On the basis of the results of DNA-DNA hybridization the strains were divided into four genetic groups.

Taxonomical examination and characterization of a methanol-utilizing yeast.

The morphological, cultural, and physiological characteristics are described of a yeast, LI70, which uses methanol as its source of energy and carbon; these characteristics have made it possible to identify the strain as Candida boidinii Ramirez. The identification was confirmed by a DNA-DNA genetic homology of 99.43% with the type strain of C. boidinii. Strain LI70 is not pathogenic.