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PubMed2000

Lactic acid permeabilizes gram-negative bacteria by disrupting the outer membrane.

The effect of lactic acid on the outer membrane permeability of Escherichia coli O157:H7, Pseudomonas aeruginosa, and Salmonella enterica serovar Typhimurium was studied utilizing a fluorescent-probe uptake assay and sensitization to bacteriolysis. For control purposes, similar assays were performed with EDTA (a permeabilizer acting by chelation) and with hydrochloric acid, the latter at pH values corresponding to those yielded by lactic acid, and also in the presence of KCN. Already 5 mM (pH 4.0) lactic acid caused prominent permeabilization in each species, the effect in the fluorescence assay being stronger than that of EDTA or HCl. Similar results were obtained in the presence of KCN, except for P. aeruginosa, for which an increase in the effect of HCl was observed in the presence of KCN. The permeabilization by lactic and hydrochloric acid was partly abolished by MgCl(2). Lactic acid sensitized E. coli and serovar Typhimurium to the lytic action of sodium dodecyl sulfate (SDS) more efficiently than did HCl, whereas both acids sensitized P. aeruginosa to SDS and to Triton X-100. P. aeruginosa was effectively sensitized to lysozyme by lactic acid and by HCl. Considerable proportions of lipopolysaccharide were liberated from serovar Typhimurium by these acids; analysis of liberated material by electrophoresis and by fatty acid analysis showed that lactic acid was more active than EDTA or HCl in liberating lipopolysaccharide from the outer membrane. Thus, lactic acid, in addition to its antimicrobial property due to the lowering of the pH, also functions as a permeabilizer of the gram-negative bacterial outer membrane and may act as a potentiator of the effects of other antimicrobial substances.

Cell Membrane↗
PubMed2001

Optimisation of media and cultivation conditions for L(+)(S)-lactic acid production by Lactobacillus casei NRRL B-441.

Process variables and concentration of carbon in media were optimised for lactic acid production by Lactobacillus casei NRRL B-441. Lactic acid yield was inversely proportional to initial glucose concentration within the experimental area (80-160 g l(-1)). The highest lactic acid concentration in batch fermentation, 118.6 g l(-1), was obtained with 160 g 1(-1) glucose. The maximum volumetric productivity, 4.4 g 1(-1) h(-1) at 15 h, was achieved at an initial glucose concentration of 100 g l(-1). Similar lactic acid concentrations were reached with a fedbatch approach using growing cells, in which case the fermentation time was much shorter. Statistical experimental design and response surface methodology were used for optimising the process variables. The temperature and pH optima for lactic acid production were 35 degrees C, pH 6.3. Malt sprout extract supplemented with yeast extract (4 g l(-1)) appeared to be an economical alternative to yeast extract alone (22 g l(-1)) although the fermentation time was a little longer. The results demonstrated both the separation of the growth and lactic acid production phases and lactic acid production by non-growing cells without any nutrient supplements. Resting L. casei cells converted 120 g l(-1) glucose to lactic acid with 100% yield and a maximum volumetric productivity of 3.5 g l(-1) h(-1).

Culture Media↗
PubMed2002

Analysis and practical implementation of a model for combined growth and metabolite production of lactic acid bacteria.

Next to the traditional application of lactic acid bacteria (LAB) as starter cultures for food fermentations, the use of LAB as protective cultures against microbial pathogens and spoilage organisms in other food production processes gains more and more interest. The inhibitory effect of LAB is mainly accomplished through formation of antimicrobial metabolites. In this paper, the model of Nicolaï et al. [Food Microbiol. 10 (1993) 229.], describing cell growth and production of lactic acid, which is the major end-product of LAB metabolism, is investigated. In contrast to classical predictive models, the transition of the exponential growth phase to the stationary phase is obtained through the increasing concentrations of undissociated lactic acid [LaH] and decreasing pH in the environment. To describe the variation in time of [LaH] and pH, a novel, robust calculation method is introduced. The model of Nicolaï et al. in combination with the novel method of [LaH] and pH computation is then further applied to an experimental data set of Lactococcus lactis SL05 grown in a rich medium. An accurate description of the measured values of cell concentration, total lactic acid concentration and pH is obtained.

Cell Division↗
PubMed1980

Topical mosquito repellents XIII: Cyclic analogs of lactic acid.

Numerous cyclic analogs of lactic acid were synthesized to ascertain whether they might act as agonists of antagonists of lactic acid, a known attractant for mosquitoes. These compounds were evaluated with an in vitro blood-feeding test system and an in vivo cloth test. Two of the compounds in the blood-feeding test system showed biphasic results, acting as attractants at low concentrations and as repellents at higher concentrations. Several compounds (III, V, VII, and X) repelled Aedes aegypti mosquitoes in the blood-feeding test system. However, in the in vivo cloth test system, only III repelled the mosquitoes significantly.

Aedes↗
PubMedDate not supplied

A new strategy for recycling and preparation of poly(L-lactic acid): hydrolysis in the melt.

Poly(L-lactide) [i.e., poly(L-lactic acid) (PLLA)] was hydrolyzed in the melt in high-temperature and high-pressure water at the temperature range of 180-350 degrees C for a period of 30 min, and formation, racemization, and decomposition of lactic acids and molecular weight change of PLLA were investigated. The highest maximum yield of l-lactic acid, ca. 90%, was attained at 250 degrees C in the hydrolysis periods of 10-20 min. Too-high hydrolysis temperatures such as 350 degrees C induce the dramatic racemization and decomposition of formed lactic acids, resulting in decreased maximum yield of L-lactic acid. The hydrolysis of PLLA proceeds homogeneously and randomly via a bulk erosion mechanism. The molecular weight of PLLA decreased exponentially without formation of low-molecular-weight specific peaks originating from crystalline residues. The activation energy for the hydrolysis (deltaE(h)) of PLLA in the melt (180-250 degrees C) was 12.2 kcal x mol(-1), which is lower than 20.0 kcal x mol(-1) for PLLA and 19.9 kcal x mol(-1) for poly(dl-lactide) [i.e., poly(DL-lactic acid)] as a solid in the temperature range below the glass-transition temperature (21-45 degrees C). This study reveals that hydrolysis of PLLA in the melt is an effective and simple method to obtain l-lactic acid and to prepare PLLA having different molecular weights without containing the specific low-molecular-weight chains, because of the removal of the effect caused by crystalline residues.

Hydrolysis↗
PubMed1992

In vitro erosion of 20 commercial glass ionomer cements measured using the lactic acid jet test.

The lactic acid jet test has been proposed for incorporation in international standards for dental cements, since results correlate well with in vivo erosion. In the literature, jet test results have been reported on only six glass ionomer cements. This study examines three types of glass ionomer, restorative, luting and metal reinforced, twenty materials from six manufacturers. A wide range of erosion rates was found particularly for restorative cements. The hypotheses put forward by previous workers to explain differences in erosion rates found on their limited range of glass ionomers do not apply to the wider range that we tested.

Biocompatible Materials↗
PubMed1986

Use of D-lactic acid measurements in the diagnosis of bacterial infections.

This study explored the use of D-lactic acid as a marker for bacterial infections. D-Lactic was produced by frequently encountered human bacterial pathogens under anaerobic growth conditions; Bacteroides fragilis produced the largest amount. Orally administered D-lactic acid was absorbed from the intestines of rats and later found in measurable quantities in the blood and urine. Eunephric and anephric rats that received D-lactic acid intravenously showed similar quantities of this metabolite in the blood. These quantities are consistent with the distribution of D-lactic acid to total body water. Isolated liver and lung tissues from rats did not metabolize or produce D-lactic acid. Rats with experimentally induced, sublethal klebsiella peritonitis had D-lactic acidemia of 0.2 mM and 25.6 mM at 0 and 6 hr of infection, respectively. In a normal human, D-lactic acid was detected in the urine and blood after a subcutaneous injection of D-lactic acid, and pharmacokinetics of elimination similar to those of rats were found.

Anaerobiosis↗
PubMed2004

Effect of process variables on particle size of gelatin microspheres containing lactic acid.

Gelatin microspheres containing lactic acid were prepared by a polymerization technique using glutaraldehyde as the cross-linking agent. Because particle size distribution of microspheres is a vital factor in the characterization of microspheres, the present study was carried out to evaluate the effect of process variables on the microspheres size distribution. It was found that concentration of a gelatin solution is the most important parameter that influences the particle size of microspheres. By using different concentrations of gelatin solution, microspheres with different size ranges were prepared. Both the stirring rate of the system and the volume ratio of aqueous and oil phases exerted a great influence on microsphere-size distribution, whereas, cross-linking time and cross-linker concentration only affected the yield. Lower-phase volume ratios resulted in small uniform microspheres with smooth surfaces and a narrow size range. The effect of emulsifier concentration (span 80), below 1% (w/w, with respect to the weight of the oil phase), on particle size was appreciable. However, at higher concentrations, little effect was observed.

Cross-Linking Reagents↗
PubMed2004

Novel mechanism of tumorigenesis: increased transforming growth factor-beta 1 suppresses the expression of connexin 43 in BALB/cJ mice after implantation of poly-L-lactic acid.

Poly-L-lactic acid (PLLA) is a widely used promising material for surgical implants such as tissue-engineered scaffolds. In this study, we aimed to determine the in vivo effect of PLLA plates on the cellular function of subcutaneous tissue in the two mouse strains, BALB/cJ and SJL/J, higher and lower tumorigenic strains, respectively. Gap-junctional intercellular communication (GJIC) and the expression of connexin 43 (Cx43) protein were significantly suppressed, whereas the secretion of transforming growth factor-beta 1 (TGF-beta 1) level was significantly increased in PLLA-implanted BALB/cJ mice compared with BALB/cJ controls. However, no significant difference in TGF-beta 1 secretion was observed between the SJL/J-implanted and SJL/J control mice. We found for the first time that a significant difference was observed between the two strains; thus, the PLLA increased the secretion of TGF-beta 1 and suppressed the mRNA expression of Cx43 at the earlier stage after implantation into the higher-tumorigenic strain, BALB/cJ mice. This novel mechanism might have a vital role in the inhibition of GJIC and promote the tumorigenesis in BALB/cJ mice.

Animals↗
PubMed1993

[A basic study on usefulness of bleomycin incorporated in poly DL-lactic acid].

Poly DL-lactic acid (PLA) is one of the biodegradable polymers. Bleomycin (BLM) incorporated into small cylinders of PLA blends was prepared as a new dosage (BLM-PLA). When BLM-PLA was preserved in saline, the dissolution rate of BLM from BLM-PLA was 49.2% after 7 days, 85.2% after 14 days and 99.7% after 21 days, respectively. BLM-PLA was implanted subcutaneously into the back of 36 rats. On days 3, 7, 14, 21, 28 and 35, the connective tissues near the implants, lymph node, lung, liver and kidney were removed and BLM activity was measured. The BLM concentration was maintained at a high level in the connective tissues until 14 days, and in the lymph node between 21 and 28 days. On the other hand, the BLM level was low in the lung, liver and kidney. Consequently, it was suggested that PLA is useful as a carrier for drug delivery system and that administration of BLM-PLA is an effective anti-cancer modality, especially in local chemotherapy.

Animals↗
PubMed1993

Carrier-mediated transport of lactic acid in cultured neurons and astrocytes.

The glycolytic end product lactic acid induced a rapid transient decrease in cytosolic pH in cultured neurons and astrocytes, as measured by microspectrofluorometry using the fluorescent indicator dye 2',7'-bis-(2-carboxyethyl)-5-(and-6) carboxyfluorescein acetoxymethyl ester. Over a physiological range of pH, the initial rate of cellular acidification was a saturable function of the extracellular lactate concentration, suggesting that a saturable transport system mediated lactic acid permeation across the plasma membrane. This transport process displayed stereoselectivity, with a threefold higher rate of intracellular acidification by L-lactic acid than by its D-isomer. Lactic acid-induced acidification occurred in the absence of intracellular ATP, suggesting that transport proceeded independently of the cellular energy charge. These data suggest the existence of a lactic acid carrier in mammalian neuronal and astrocytic plasma membranes, which might serve an acid-scavenging function under conditions of altered pH homeostasis. In the setting of in vivo cerebral ischemia, this carrier may promote the efflux of lactic acid from astrocytes, redistributing it among less metabolically active neurons.

Animals↗
PubMed2006

In vitro flexural properties of hydroxyapatite and self-reinforced poly(L-lactic acid).

Poly(L-lactic acid) (PLLA) has been used for fracture fixation devices, but its use is limited because of its poor biocompatibility and mechanical properties. The effects of extrusion, incorporation of hydroxyapatite (HA) and self-reinforced composites (SRCs) on the resultant mechanical properties of PLLA were examined. Samples were conditioned for up to 52 weeks in PBS at 37 degrees C. Extrusion did not adversely affect the mechanical properties of PLLA. After in vitro conditioning, a slight but significant reduction in the strain to failure and modulus was seen. HA (10-40%) by weight was evenly distributed into PLLA using an intermeshing twin-screw extruder. As ceramic content increased, the initial modulus increased but flexural strength decreased. After immersion, the modulus of all HA-PLLA blends was lower than PLLA. HA particles did not form a strong bond with the PLLA, which promoted easier degradation of the HA-PLLA matrix. SRCs showed a higher modulus and strength when compared to all materials except the modulus of 30 and 40% HA-PLLA composites before immersion. Water preferentially attacked the matrix of the composite, leading to more fiber pullout, but the fiber orientation maintained the advantages in strength and modulus up to 24 weeks in vitro.

Biocompatible Materials↗
PubMed2004

Strain improvement and metabolic flux analysis in the wild-type and a mutant Lactobacillus lactis strain for L(+)-lactic acid production.

The effects of initial glucose concentration and calcium lactate concentration on the lactic acid production by the parent strain, Lactobacillus lactis BME5-18, were studied. The results of the experiments indicated that glucose and lactate repressed the cell growth and the lactic acid production by Lactobacillus lactis BME5-18. A L(+)-lactic acid overproducing strain, Lactobacillus lactis BME5-18M, was screened by mutagenizing the parent strain with ultraviolet (UV) light irradiation and selecting the high glucose and lactate calcium concentration repression resistant mutant. Starting with a concentration of 100g L(-1) glucose, the mutant produced 98.6 g L(-1) lactic acid after 60 h in flasks, 73.9% higher than that of the parent strain. The L(+)-lactic acid purity was 98.1% by weight based on the amount of total lactic acid. The culture of the parent strain could not be analyzed well by conventional metabolic flux analysis techniques, since some pyruvate were accumulated intracellularly. Therefore, a revised flux analysis method was proposed by introducing intracellular pyruvate pool. Further studies demonstrate that there is a high level of NADH oxidase activity (12.11 mmol mg(-1) min(-1)) in the parent strain. The molecular mechanisms of the strain improvement were proposed, i.e., the high level of NADH oxidase activity was eliminated and the uptake rate of glucose was increased from 82.1 C-mmol (g DW h)(-1) to 98.9 C-mmol (g DW h)(-1) by mutagenizing the parent strain with UV, and therefore the mutant strain converts mostly pyruvate to lactic acid with a higher productivity (1.76 g L(-1) h(-1)) than the parent strain (0.95 g L(-1) h(-1)).

Computer Simulation↗
PubMed1988

Regulation of lactic acid production during exercise.

Lactic acid accumulates in contracting muscle and blood beginning at approximately 50-70% of the maximal O2 uptake, well before the aerobic capacity is fully utilized. The classical explanation has been that part of the muscle is O2 deficient and therefore lactate production is increased to provide supplementary anaerobically derived energy. Currently, however, the predominant view is that lactate production during submaximal dynamic exercise is not O2 dependent. In the present review, data and arguments in support of and against the hypothesis of O2 dependency have been scrutinized. Data underlying the conclusion that lactate production during exercise is not O2 dependent were found to be 1) questionable, or 2) interpretable in an alternative manner. Experiments in human and animal muscles under various conditions demonstrated that the redox state of the muscle is reduced (i.e., NADH is increased) either before or in parallel with increases in muscle lactate. Based on experimental data and theoretical considerations, it is concluded that lactate production during submaximal exercise is O2 dependent. The amount of energy provided through the anaerobic processes during steady-state submaximal exercise is, however, low, and the role of lactate formation as an energy source is of minor importance. It is proposed that the achievement of increased aerobic energy formation under conditions of limiting O2 availability requires increases of ADP, Pi, and NADH and that the increases in ADP (and therefore AMP via the adenylate kinase equilibrium) and Pi will stimulate glycolysis, and the resulting increase in cytosolic NADH will shift the lactate dehydrogenase equilibrium toward increased lactate production.

Animals↗
PubMed2006

Role of broiler carcasses and processing plant air in contamination of modified-atmosphere-packaged broiler products with psychrotrophic lactic acid bacteria.

Some psychrotrophic lactic acid bacteria (LAB) are specific meat spoilage organisms in modified-atmosphere-packaged (MAP), cold-stored meat products. To determine if incoming broilers or the production plant environment is a source of spoilage LAB, a total of 86, 122, and 447 LAB isolates from broiler carcasses, production plant air, and MAP broiler products, respectively, were characterized using a library of HindIII restriction fragment length polymorphism (RFLP) patterns of the 16 and 23S rRNA genes as operational taxonomic units in numerical analyses. Six hundred thirteen LAB isolates from the total of 655 clustered in 29 groups considered to be species specific. Sixty-four percent of product isolates clustered either with Carnobacterium divergens or with Carnobacterium maltaromaticum type strains. The third major product-associated cluster (17% of isolates) was formed by unknown LAB. Representative strains from these three clusters were analyzed for the phylogeny of their 16S rRNA genes. This analysis verified that the two largest RFLP clusters consisted of carnobacteria and showed that the unknown LAB group consisted of Lactococcus spp. No product-associated LAB were detected in broiler carcasses sampled at the beginning of slaughter, whereas carnobacteria and lactococci, along with some other specific meat spoilage LAB, were recovered from processing plant air at many sites. This study reveals that incoming broiler chickens are not major sources of psychrotrophic spoilage LAB, whereas the detection of these organisms from the air of the processing environment highlights the role of processing facilities as sources of LAB contamination.

Atmosphere↗
PubMed1995

Intracellular Ca2+ transients evoked by lactic acid in cultured mammalian neurons.

During cerebral ischemia, accumulation of the glycolytic end product lactic acid may contribute to brain infarction. In vitro, lactic acid evokes a process of slowly evolving neuronal death characterized by a transient maintenance of cellular viability after initial injury. We examined effects of lactic acid on intracellular Ca2+ (Cai2+). Cultured neurons loaded with the fluorescent Ca2+ indicator fura 2 showed a marked increase in Cai2+ to as high as 600 nM. This increase occurred after lactic acid exposure when intracellular pH had normalized. Membrane potential was unaltered during this period, indicating that the Cai2+ increment was not a result of membrane depolarization. Increase in Ca2+ was prevented by incubating cultures in Ca(2+)-free solutions or exposing them to the L-type Ca2+ channel antagonist nimodipine. Cai2+ returned to resting levels within 20 min and remained normal during the remainder of the 4-h observation period. Neuronal Ca2+ homeostasis was disrupted after lethal exposure to lactic acid, in that subsequent exposure to 50 mM K+ failed to increase neuronal Cai2+. Cai2+ increment was integrated over a 20-min period to obtain a measure of neuronal Cai2+ load. This "calcium integral" was found to correlate directly with severity of neuronal damage observed 24 h later. Thus the Cai2+ increase integrated over time closely reflected the likelihood of lethal neuronal injury after lactic acid exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

[Determination of enantiomeric purity for lactic acid in fermentation broth by Rhizopus oryzae with high performance liquid chromatography].

A procedure for the resolution of DL-lactic acid and the determination of D-isomer ratio in L-lactic acid fermentation broth by Rhizopus oryzae is described. The effects of pH of mobile phase and concentration of chiral mobile phase additives on resolution of DL-lactic acid were investigated. The optical isomers of lactic acid were resolved by RP-HPLC with 2,3,6-tri-O-beta-cyclodextrin(TM-beta-CD) as a chiral mobile phase additive, and C18 column as stationary phase, and detected at wavelength 210 nm. The results showed that a correction factor should be introduced into the equation for calculation of the percentage of D-lactic acid, because the UV absorption of D-lactic acid and L-lactic acid might not be the same when TM-beta-CD was present. Quantitation was achieved with external standard method, the average recovery was 100.4%, and the relative standard deviation was 0.82%. This method can be used for the determination of the percentage of D-isomer in L-lactic acid fermentation broth by Rhizopus oryzae, and it is simple, rapid and accurate. The results showed that the mass fraction of D-isomer in the fermented broth increased during the period of storage.

Chromatography, High Pressure Liquid↗
PubMed1988

Genetics of proteinases of lactic acid bacteria.

Because it is essential for good growth with concomitant rapid acid production, and for the production of flavorous peptides and amino acids, the proteolytic ability of lactic acid bacteria is of crucial importance for reliable dairy product quality. In view of this importance, considerable research has been carried out to characterize the enzymes involved. The intensified genetic research in the lactic acid streptococci and the development of gene cloning systems for these organisms have resulted in a rapid increase of genetic data on lactic streptococcal proteinases. By now, an evaluation of the biochemical, immunological and genetic data seems to be feasible. These data are discussed and integrated into a working model tentatively explaining some of the characteristics of the proteolytic systems of lactic acid streptococci.

Base Sequence↗