Acetaldehyde Production by Strains Used as Probiotics in Fermented Milk.

Lactic acid bacteria have diverse shunts for the metabolism of acetaldehyde, which is involved in the metabolism of carbohydrates, proteins and nucleic acids. In Lactobacillus acidophilus and Lactobacillus casei , strains isolated from feces of healthy children, acetaldehyde can be formed from different sources. Phosphotransacetilase, acetate kinase, aldehyde dehydrogenase and 2-deoxiriboaldolase activities were found in both strains. α-Carboxilase and threonine aldolase activities only occurred in L. acidophilus . In contrast, phosphoketolase activity was present in L. casei , but absent in the other strain studied. The accumulation of acetaldehyde in the growth medium is possible because the enzymes specific activities to form it are higher than those able to convert it to ethanol.

The Oral Administration of Lactic Acid Bacteria Increase the Mucosal Intestinal Immunity in Response to Enteropathogens.

The present studies were designed to investigate the effect of orally administered Lactobacillus casei , Lactobacillus acidophilus , Lactobacillus delbrueckii spp., bulgaricus , and Streptococcus salivarius ssp. thermophilus on local mucosal immunity in response to enteropathogens. Normal mice were protected against Salmonella typhimurium infection by previous feeding with L. casei and S. salivarius spp. thermophilus , while L. acidophilus and L. delbrueckii spp. bulgaricus were not effective. The protective effect of L. casei against S. typhimurium was associated mainly to IgA production in intestinal secretions. We observed significant differences in the intestinal fluid anti- Salmonella agglutinin titers between the Salmonella -challenged control group (without lactobacilli feeding) and mice pretreated with L. casei . The level of immunoglobulins from intestinal fluid of mice fed previously with lactic acid bacteria was measured by radial immunodiffusion assay showing in all cases an increase in the immunoglobulin concentrations. By Immunoelectrophoresis methods, we observed the presence of two lines of immunoprecipitation. When we used monospecific serum, we detected the presence of IgG and IgA. Elisa tests showed high levels of IgA to S. typhimurium in intestinal secretions of mice pretreated with L. casei , while L. acidophilus and L. delbrueckii spp. bulgaricus groups showed values at slightly higher levels than the controls. The levels of IgG to S. typhimurium were similar to controls in all cases. We did not observe antibodies against the pathogen in intestinal fluid from mice fed with S. salivarius spp. thermophilus . However, we detected anti- Streptococcus antibodies. These results show that only L. casei increases the IgA production secreted to the intestinal lumen, providing adequate defenses at mucosal surfaces, and suggest that this microorganism could be used as oral adjuvant especially to prevent enteric infections.

Peptide Hydrolases of Propionibacteria: Effect of pH and Temperature.

A comparative study of the activity of peptidases belonging to the four classic propionibacteria species cultured in milk was carried out at different values of pH and temperature. Leucine aminopeptidase and proline iminopeptidase showed greater activity in Propionibacterium freudenreichii than in the other species studied. With the single exception of Propionibacterium jensenii , the propionibacteria peptidase tested exhibited greater affinity for proline than for leucine-p-nitroanilide. Optimum temperature and pH in relation to the activity of both substrates varied according to the species under consideration.

Acid Production and Proteolytic Activity of Lactobacillus Strains Isolated from Dry Sausages.

The acid-producing capacity and proteolytic activity of 13 strains of Lactobacillus plantarum and 5 strains of Lactobacillus casei isolated from dry sausages was determined at different temperatures and at different NaCl concentrations. Most strains exhibited a maximum acid-producing rate at 30°C. According to the acidification rate at this temperature, strains were divided into three rate groups: fast (I), medium (II) and slow (III), with titratable acidity values above 1.7, between 0.7 and 1.4, and below 0.7, respectively. The decrease in pH ranged between 3.1 and 3.95 according to the group to which the strains belonged. The addition of 3% NaCl produced a marked decrease in the rate of acidification for strains in group II, a slight decrease for those in group I and no effect for those in group III. The proteolytic activity of the strains under study reached a maximum at 40°C, with values between 5.2 and 10 mg% tyrosine released. At 30°C, and in the presence of 3% NaCl, the greatest activity (5.4 mg% tyrosine) was observed in L. plantarum GV 417 and the lowest (3.4 mg% tyrosine) in L. plantarum GV 420. A decrease of approximately 80% in proteolytic activity for all strains was observed in the presence of 5% NaCl.

An Orange-Reddish Pigmentation in Roquefort Cheese.

The presence of an anomalous orange-reddish coloration in Roquefort cheese during its ripening period was studied. No pigmented colonies were isolated from milk, curd, or cheeses after pressing, but their presence in relatively large numbers was observed after salting (7 d) up to the end of the ripening process (90 d). About 37% of the strains isolated (32 in all) were orange-pigment producers in light as well as in the dark (type I), whereas about 25% produced an orange coloration only in the light (type II). No production of pigment was observed at pH 6.0 or below in the absence of sodium chloride, and the highest color intensity was registered at pH 7.0 in the presence of sodium chloride. Morphological and physiologic studies of the orange-pigmented strains revealed that most of them were closely related to Brevibacterium linens .

Effect of a Mixture of Lactobacillus casei and Lactobacillus acidophilus Administered Orally on the Immune System in Mice.

The effects of an orally-administered mixture of Lactobacillus casei and Lactobacillus acidophilus on the immune system in Swiss albino mice were studied. Non-fermented milk containing viable cultures of both microorganisms was fed for different consecutive days to the animals, the effect of such feeding on their immune system was evinced by macrophage and lymphocyte activation. An increase both in the in vitro phagocytic activity of peritoneal macrophages and in the carbon clearance activity was observed. As regard the lymphocytic activity, the mixture produced a higher activation than that in the control mice. The enhanced macrophage and lymphocytic activity by administering cultures via the oral route, suggest the advisability of using the mixture of bacteria for a more efficient stimulation of the host immune response.