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Amongst 100 isolates of lactic acid bacteria, Lactobacillus bulgaricus and Streptococcus feacalis proved to be highly proteolytic as demonstrated by starch gel electrophoresis and liberation of various amino acids. Both these organisms hydrolysed casein differently to produce different concentrations of amino acids.
The effect of implantation of poly-(L-lactic) acid membranes after palatal surgery on dentoalveolar development was investigated. Beagle dogs were randomly assigned to four experimental groups and a control group. In the experimental groups, a soft tissue defect was created in the medial region of the palate by excising a standardized elliptical mucoperiosteal flap at 12 weeks of age. This defect was closed according to the Von Langenbeck technique, leaving two areas of denuded bone. Poly-(L-lactic) acid membranes were implanted on the denuded bony areas either directly or 3 weeks after surgery. Group L and LS served as sham groups. Dental casts were made at regular intervals until 25 weeks of age, and maxillary arch dimensions were studied. Dental arch dimensions in the deciduous dentition of the experimental groups were not markedly disturbed, but after transition of teeth, mainly transversal maxillary arch dimensions in the premolar region were reduced. It was concluded that implantation of poly-(L-lactic) acid membranes after palatal surgery in Beagle dogs did not prevent iatrogenic disturbances of dentoalveolar development under conditions used in this study.
The tumor milieu can influence dendritic cell (DC) differentiation. We analyzed DC differentiation in a 3-dimensional tumor model and propose a new mechanism of DC modulation by the tumor environment. Monocytes were cultured in the presence of IL-4 and GM-CSF within multicellular tumor spheroids (MCTSs) generated from different tumor cell lines. Monocytes invaded the MCTSs and differentiated into tumor-associated dendritic cells (TADCs). The antigen expression was altered on TADCs independent of the culture conditions (immature/mature DCs, Langerhans cells) and IL-12 secretion was reduced. Supernatants of MCTSs could partially transfer the suppressive effect. Conditioned media from urothelial carcinoma cell lines contained high levels of M-CSF and IL-6, both cytokines known to modulate DC differentiation. In contrast, melanoma and prostate carcinoma MCTS cocultures produced little M-CSF and IL-6, but high levels of lactic acid. Indeed, addition of lactic acid during DC differentiation in vitro induced a phenotype comparable with TADCs generated within melanoma and prostate carcinoma MCTSs. Blocking of lactic acid production in melanoma MCTS cocultures reverted the TADC phenotype to normal. We therefore conclude that tumor-derived lactic acid is an important factor modulating the DC phenotype in the tumor environment, which may critically contribute to tumor escape mechanisms.
Lactic acid bacteria (LAB) fight competing Gram-positive microorganisms by secreting anti-microbial peptides called bacteriocins. Peptide bacteriocins are usually divided into lantibiotics (class I) and non-lantibiotics (class II), the latter being the main topic of this review. During the past decade many of these bacteriocins have been isolated and characterized, and elements of the genetic mechanisms behind bacteriocin production have been unravelled. Bacteriocins often have a narrow inhibitory spectrum, and are normally most active towards closely related bacteria likely to occur in the same ecological niche. Lactic acid bacteria seem to compensate for these narrow inhibitory spectra by producing several bacteriocins belonging to different classes and having different inhibitory spectra. The latter may also help in counteracting the possible development of resistance mechanisms in target organisms. In many strains, bacteriocin production is controlled in a cell-density dependent manner, using a secreted peptide-pheromone for quorum-sensing. The sensing of its own growth, which is likely to be comparable to that of related species, enables the producing organism to switch on bacteriocin production at times when competition for nutrients is likely to become more severe. Although today a lot is known about LAB bacteriocins and the regulation of their production, several fundamental questions remain to be solved. These include questions regarding mechanisms of immunity and resistance, as well as the molecular basis of target-cell specificity.
The ability of dromedary skim milk to form an acid curd during a lactic acid starter fermentation was investigated. The activity of the starter in dromedary milk was characterized by a longer lag phase ( approximately 5 vs. approximately 1 h) and by an earlier decline phase. This suggests the presence of inhibiting factors. The maximum buffering capacity of dromedary milk as well as its minimum apparent viscosity were obtained at lower pH values. Similarly, its elastic modulus appeared later (pH 5.7 vs. 6.3). Because these rheological and biochemical events took place at lower pH values, dromedary skim milk seems to present a higher physical stability toward the increase of acidity. Determination of the rheological and microscopic characteristics of the dromedary milk coagulum (pH 4.4) did not reveal curd formation but indicated a fragile and heterogeneous structure. This coagulum, which is very different from that of cows' milk, seems to be made up of dispersed casein flakes.
To increase the acceptability of food products containing genetically modified microorganisms it is necessary to provide in an early stage to the consumers that the product is safe and that the product provide a clear benefit to the consumer. To comply with the first requirement a systematic approach to analyze the probability that genetically modified lactic acid bacteria will transform other inhabitants of the gastro- intestinal (G/I) tract or that these lactic acid bacteria will pick up genetic information of these inhabitants has been proposed and worked out to some degree. From this analysis it is clear that reliable data are still missing to carry out complete risk assessment. However, on the basis of present knowledge, lactic acid bacteria containing conjugative plasmids should be avoided. Various studies show that consumers in developed countries will accept these products when they offer to them health or taste benefits or a better keepability. For the developing countries the biggest challenge for scientists is most likely to make indigenous fermented food products with strongly improved microbiological stability due to broad spectra bacteriocins produced by lactic acid bacteria. Moreover, these lactic acid bacteria may contribute to health.
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The level of intermediates of glycolysis (hexose monophosphates, fructose-1,6-diphosphate, pyruvate) and the rate of lactic acid synthesis (under the aerobic conditions without substrates and in the presence of glucose, glucose-6-phosphate and fructose-1,6-diphosphate) were measured in the eye tissues (retina, iris, ciliary bodies, uvea) of rabbits of different age. The rate of lactic acid synthesis under the aerobic conditions in the retina and uveal tract increases of the latter the rate of lactic acid synthesis was the highest. The greatest increase in the lactic acid content was observed during the first 15 days of postnatal development.
Novel solid supports, consisting of polypropylene blended with various agricultural materials (pp composite), were evaluated as supports for pure- and mixed-culture continuous lactic acid fermentations in biofilm reactors. Streptomyces viridosporus T7A (ATCC 39115) was used to form a biofilm, and Lactobacillus casei subsp. rhamnosus (ATCC 11443) was used for lactic acid production. For mixed-culture fermentations, a 15-day continuous fermentation of S. viridosporus was performed initially to establish the biofilm. The culture medium was then inoculated with L. casei subsp. rhamnosus. For pure-culture fermentation, L. casei subsp. rhamnosus was inoculated directly into the reactors containing sterile pp composite chips. The biofilm reactors containing various pp composite chips were compared with a biofilm reactor containing pure polypropylene chips and with a reactor containing a suspension culture. Continuous fermentation was started, and each flow rate (0.06 to 1.92 ml/min) was held constant for 24 h; steady state was achieved after 10 h. Lactic acid production was determined throughout the 24-h period by high-performance liquid chromatography. Production rates that were two to five times faster than those of the suspension culture (control) were observed for the pure- and mixed-culture bioreactors. Both lactic acid production rates and lactic acid concentrations in the culture medium were consistently higher in mixed-culture than in pure-culture fermentations. Biofilm formation on the chips was detected at harvest by chip clumping and Gram staining.
OBJECTIVES: The aim of this study was to determine the interaction of four polyacid-modified resin composites with aqueous lactic acid solutions, and to compare changes with those for a glass-ionomer cement and a conventional resin composite. METHODS: For each material, namely Compoglass F, Dyract AP, Hytac and Ana Compomer, plus AquaCem (glass-ionomer cement) and Pekafil (conventional composite resin), five cylindrical specimens of 4 mm diameter x 6 mm height were prepared and weighed. They were stored individually in 2.0 cm3 of 0.02 mol l-1 lactic acid solution for 1 week then the pH was determined and the specimens reweighed. The lactic acid solution was replenished, and the specimens were stored for a further week, after which the pH and specimen weights were again measured. This was repeated at 1 week intervals until the specimens were 6 weeks old. Differences were analysed by ANOVA followed by Newman-Keuls post hoc analysis. RESULTS: All four polyacid-modified composites increased the pH of the solutions at all time intervals by at least 0.26 pH units (significant to at least p < 0.01). This effect was similar to that of the glass-ionomer (but significantly less, p < 0.05) while significantly greater (p < 0.05) than that for the composite, Pekafil, which, by contrast, had no effect on pH. The observed rise in pH reduced significantly over time (ANOVA, p < 0.05). After 1 week, all pH changes were accompanied by net reductions in specimen mass, indicating susceptibility to acid erosion. Hytac was significantly more resistant to this erosion than the other materials; conversely, it had the least effect on solution pH. SIGNIFICANCE: These results show that polyacid-modified resin composites neutralise lactic acid in vitro but suffer erosion in the process.
The ability of poly(lactic acid) (PLA) to serve as a long-term source of lactic acid for bacterial sulfate reduction activity in zinc smelter tailings was investigated. Solid PLA polymers mixed in water hydrolyzed abiotically to release lactic acid into solution over an extended period of time. The addition of both PLA and gypsum was required for indigenous bacteria to lower redox potential, raise pH, and stimulate sulfate reduction activity in highly oxidized smelter tailings after one year of treatment. Bioavailable cadmium, copper, lead and zinc were all lowered significantly in PLA/gypsum treated soil, but PLA amendments alone increased the bioavailability of lead, nickel and zinc. Similar PLA amendments may be useful in constructed wetlands and reactive barrier walls for the passive treatment of mine drainage, where enhanced rates of bacterial sulfate reduction are desirable.
Biopreservation refers to extended storage life and enhanced safety of foods using the natural microflora and (or) their antibacterial products. Lactic acid bacteria have a major potential for use in biopreservation because they are safe to consume and during storage they naturally dominate the microflora of many foods. In milk, brined vegetables, many cereal products and meats with added carbohydrate, the growth of lactic acid bacteria produces a new food product. In raw meats and fish that are chill stored under vacuum or in an environment with elevated carbon dioxide concentration, the lactic acid bacteria become the dominant population and preserve the meat with a "hidden' fermentation. The same applies to processed meats provided that the lactic acid bacteria survive the heat treatment or they are inoculated onto the product after heat treatment. This paper reviews the current status and potential for controlled biopreservation of foods.
We studied antimicrobial properties of lactic acid bacteria from sour milk products Narine, Karine, and Matsun. The whey of sour milk products included two major fractions of sugars and L-lactic acid and its sodium and calcium salts. Antimicrobial activity of Narine, Karine, and Matsun was related to the presence of L-lactic acid and its sodium and calcium salts.
OBJECTIVE: To evaluate the possibility of domestic poly-DL-lactic acid membranes as barriers during periodontal guided tissue regeneration. METHODS: Two-wall intrabony defects were made by artificially removing buccal and distal alveolar bone from the distal roots of the second, third and fourth mandibular premolars as well as the first mandibular molars of dogs. These experiment defects received four membranes (PDLLA, ePTFE, COL, Vicryl ) respectively for GTR, the control treated without membrane. Animals were sacrificed for histological evaluation and histometric analysis 2,4,8 weeks after surgery. RESULTS: Domestic poly-DL-lactic acid membranes for periodontal guided tissue regeneration only induce a non-specific inflammation, which began its bioresorption at 4 weeks after surgery. Just like the other GTR materials including Vicryl mesh,domestic poly-DL-lactic acid membrane acts as barrier preventing the apical downgrowth of gingival epithelium and prompting periodontal tissue regeneration. As compared with the control, PDLLA exhibited its more effects 4 weeks after surgery, there is statistically difference between them. CONCLUSION: Domestic poly-DL-lactic acid membranes exhibit excellent biocompatibility, as a guided tissue regenerative materials, it may have beneficial effects in the treatment of 2-wall periodontal intrabony defects.
PURPOSE: The aim of this study was to evaluate the lactic acid concentration in supragingival plaque from caries-active pre-school children after a short-term use of either xylitol- or sorbitol-containing chewing gums. MATERIAL AND METHODS: The investigation consisted of a prospective crossover design with 10 healthy children aged 2-4 years each with at least two caries lesions within the dentine (ds > or = 2). The children were instructed to chew 6 pieces of a test or a control gum every day for a 14-day period. The test gum contained 65% xylitol and the control gum was sweetened with sorbitol. At baseline and after 14 days, salivary mutans streptococci were enumerated with a chair-side test (Strip mutans) and dental plaque was collected from the upper maxillary incisors. After a washout period of 6 weeks, the same procedure was repeated with the corresponding test or control gum. Lactic acid was determined enzymatically in glucose-challenged plaque suspensions. RESULTS: The lactic acid concentration was significantly reduced (p<0.05) by 22% compared with baseline following the xylitol gum regimen but was unaltered after the control gum. The levels of salivary mutans streptococci were mainly unaffected by both chewing gums. CONCLUSION: A 14-day use of xylitol-containing chewing gums, corresponding to a daily amount of 5 grams of xylitol, could diminish glucose-initiated lactic acid formation in supragingival plaque in caries-active pre-school children.
Cerebrospinal fluid (CSF) samples from 22 patients with systemic lupus erythematosus (SLE) and 20 samples from normal controls were studied for lactic acid levels. Ten samples were obtained from SLE patients with active central nervous system (CNS) involvement and 12 from SLE patients with inactive CNS disease. The mean CSF lactic acid level in patients with SLE was 17.24 +/- 1.25 mg/dl (range 31-10.2 mg/dl) which was not statistically different to the normal control mean of 14.75 +/- 0.9 mg/dl (range 9-28 mg/dl). Thus, lactic acid levels in active or inactive CNS disease of SLE appear to be normal. Due to the fact that lactic acid levels are elevated in the CSF of patients with bacterial meningitis, lactic acid levels can be of potential value in the differentiation between bacterial meningitis and CNS involvement of SLE.
Five molecular weight grades of poly(DL-lactic acid) were characterized using gel permeation chromatography, differential scanning calorimetry, and viscometry to determine the effect of molecular weight on the glass transition temperature and the intrinsic viscosity. In addition, dynamic mechanical thermal analysis was used to assess the dynamic storage modulus and the damping factor of the polymer samples by detecting motional and structural transitions over a wide temperature range. Significant relationships were found between the molecular weight and these polymer properties. The five grades of poly(DL-lactic acid) were also incorporated as binders into matrix tablet formulations containing the model drug theophylline and microcrystalline cellulose. Dissolution studies showed significant correlations between the properties of the polymer and the matrix release profiles of the tablets. The release of theophylline slowed down progressively as the polymer molecular weight increased. The differences in release became less significant and reached a limiting asymptotic value as the molecular weight increased to 138,000. Further, tablet index testing was utilized to determine the compaction properties of the polymer granulations. Although there was no correlation with the molecular weight of PLA, brittle fracture index testing indicated very low brittleness for all granulations tested. However, bonding index determinations correlated very well with both the physical-mechanical properties of the polymer and drug release profiles.
Four strains of mesophilic lactic acid bacteria were separately or coentrapped in kappa-carrageenan/locust bean gum gel beads and used for continuous prefermentation of UHT skim milk in a stirred-tank bioreactor. Lactic acid and cell productivities of the immobilized cell bioreactor were particularly high and remarkably stable during eight weeks of continuous milk prefermentation (about 18 g h-1 l-1 of lactic acid and 4.9 x 10(12) CFU h-1 l-1, respectively, but important variations of the bacterial populations is prefermented milk and gel beads occurred in any case (co-or separate entrapment). The strain Lactococcus lactis subsp. lactis biovar diacetylactis CDII became dominant, accounting for approx. 90% (released cells) and 78% (immobilized cells) of the total population. Microscopic observations of sections of gels beads showed a progressive destructing of the bead surface with rupture and release of entrapped viable cells from peripheral cavities of the gel. It is believed that these cavities close again after releasing all or part of their cell content, entrapping the different strains of the mixed culture and initiating a new colonization step and a cross-contamination of the beads. On the other hand, experimentations over seven-week periods with pasteurized milk showed the high resistance of the immobilized cell bioreactor to psychrotrophic contamination.