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PubMed1987

Lactose malabsorption and giardiasis in Basotho school children.

The prevalence of primary, adult-type, lactose malabsorption was assessed by means of the hydrogen breath test after intake of 360 ml of full cream milk (approximately 18 g lactose) in 96 randomly selected Basotho school children, aged 5-15 years. Of 86 children who did not have diarrhoea in the previous week 82 (85%) were lactose malabsorbers, while 4 (5%) could not be classified because of undetectable hydrogen excretion. Milk intolerance presenting as diarrhoea was significantly (p less than 0.01) more common in children who associated previous abdominal complaints with milk intake and/or did not like milk. A negative hydrogen breath test was significantly (p less than 0.05) more often observed in children who had diarrhoea in the previous week. Giardia was present in 18 (19%) of 93 children. The incidence of giardiasis did not correlate with the presence of lactose malabsorption in children without diarrhoea in the previous week. However, milk intolerance presenting as diarrhoea was significantly (p less than 0.05) more common in children with giardiasis. The findings support the use of physiological quantities of milk in Basotho school children.

Adolescent↗
PubMed1995

Compression of lactose, glucose and mannitol granules.

The effect of the amount of granulation liquid, compression speed and maximum compression force on then compressibility and compactibility of lactose, glucose and mannitol granules was studied. The porosity based on the geometrical shape and the uniformity of weight of tablets was also studied. Lactose and mannitol granules showed a greater compressibility than glucose granules. Mannitol granules produced the hardest tablets and lactose and glucose the weakest. The change in the amount of granulation liquid caused changes both in the granule porosity and in the amount of binder; this was attributed to differences in tablet strength. All parameters studied were relatively insensitive to changing speeds of compression in the range used, except for the breaking force of mannitol tablets, which was greatest with the lowest speed of compression. All granule masses showed a relatively good continuous flow suitable for table production. Tablets compressed from lactose granules had the best uniformity of weight of the tablets studied.

Dosage Forms↗
PubMed1987

Salt tolerance of lactose-grown Vibrio parahaemolyticus carrying Escherichia coli lac genes.

Lac- strains of Vibrio parahaemolyticus were converted to Lac+ on receiving a hybrid plasmid containing the lactose utilization genes of Escherichia coli K-12. A V. parahaemolyticus strain containing this hybrid plasmid exhibited optimal growth rates on glucose and other carbon sources in the presence of 0.2 to 0.4 M NaCl. Growth of the same strain on lactose was inhibited at similar concentrations of NaCl. The altered growth rate responses in lactose medium appeared to be attributable to effects of NaCl on the activity of lactose permease, and possibly on that of beta-galactosidase, rather than on the levels of these enzymes in V. parahaemolyticus cells.

Culture Media↗
PubMed1989

Efficient ethanol production from glucose, lactose, and xylose by recombinant Escherichia coli.

Lactose and all of the major sugars (glucose, xylose, arabinose, galactose, and mannose) present in cellulose and hemicellulose were converted to ethanol by recombinant Escherichia coli containing plasmid-borne genes encoding the enzymes for the ethanol pathway from Zymomonas mobilis. Environmental tolerances, plasmid stability, expression of Z. mobilis pyruvate decarboxylase, substrate range, and ethanol production (from glucose, lactose, and xylose) were compared among eight American Type Culture Collection strains. E. coli ATCC 9637(pLO1297), ATCC 11303(pLO1297), and ATCC 15224(pLO1297) were selected for further development on the basis of environmental hardiness and ethanol production. Volumetric ethanol productivities per hour in batch culture were 1.4 g/liter for glucose (12%), 1.3 g/liter for lactose (12%), and 0.64 g/liter for xylose (8%). Ethanol productivities per hour ranged from 2.1 g/g of cell dry weight with 12% glucose to 1.3 g/g of cell dry weight with 8% xylose. The ethanol yield per gram of xylose was higher for recombinant E. coli than commonly reported for Saccharomyces cerevisiae with glucose. Glucose (12%), lactose (12%), and xylose (8%) were converted to (by volume) 7.2% ethanol, 6.5% ethanol, and 5.2% ethanol, respectively.

DNA, Recombinant↗
PubMed1991

Identification of a new genetic determinant for cell aggregation associated with lactose plasmid transfer in Lactococcus lactis.

Derivatives of the lactose miniplasmid pMG820 were constructed in which a staphylococcal erm gene was inserted and in which this was accompanied by subsequent deletion of the lactose genes. The resulting plasmids were thus marked with both erythromycin resistance and lactose utilization genes in pF1132 or solely erythromycin resistance in pF1133. These plasmids retained the normal conjugation properties characteristic of lactose plasmid pLP712, including the generation by intermolecular rearrangement of high-frequency-transfer Clu+ derivatives which exhibited cell aggregation. The use of such Clu+ plasmids in a variety of mating experiments between different lactococcal strains and the observation of cell aggregation when particular mating mixtures were made led to the discovery of a new component of this conjugation system named Agg. A chromosomal gene agg was postulated to be present in some but not all strains of lactococci. High-frequency conjugation and cell aggregation thus depend on the presence of both Agg and Clu, although in a mating pair these components can be in the same or in separate strains. The Agg and Clu components may be analogous to the binding substance and aggregation substance that are involved in the hemolysin plasmid transfer system of Enterococcus faecalis, although control of their expression is different.

Conjugation, Genetic↗
PubMed1974

Simultaneous loss of proteinase- and lactose-utilizing enzyme activities in Streptococcus lactis and reversal of loss by transduction.

During studies on spontaneous loss of lactose metabolism in Streptococcus lactis C2, it was found that the lactose-negative (lac(-)) mutants were also proteinase negative (prt(-)). This pleiotropic effect was observed in S. diacetilactis 18-16, but not in S. cremoris B1. The lac(-)prt(-) mutants from S. lactis C2 were able to grow in milk, but no pH change or measurable protein breakdown occurred. When the milk was supplemented with glucose, a slow decline in pH occurred. Addition of a protein hydrolysate to milk did not stimulate acid production. When both supplements were added to milk, normal growth and pH change were obtained. When the lac(-)prt(-) mutant of S. lactis C2 was transduced with the temperate phage from the lac(+)prt(+) parent culture, approximately equal numbers of lac(+)prt(-) and lac(+)prt(+) transductants were obtained. When the spontaneous lac(+)prt(-) strain of S. lactis C2 was converted to a lac(-)prt(-) derivative and transduced, similar results were obtained. The co-transduction of the lactose and proteinase markers suggest they are closely associated. The findings indicate that the transducing phage from S. lactis C2 can be used to examine the causes of instability in both the lactose and proteinase enzyme systems of this organism.

Animals↗
PubMed1981

Lactose-reversible coaggregation between oral actinomycetes and Streptococcus sanguis.

Freshly isolated strains of oral actinomycetes were obtained from human dental plaque and were tested for the ability to coaggregate with common laboratory stock strains of Streptococcus sanguis. Strains belonging to the genera Actinomyces, Arachnia, Bifidobacterium, and Bacterionema were isolated. Only members of the genus Actinomyces coaggregated with the streptococci, and only Actinomyces viscosus and Actinomyces naeslundii exhibited lactose-reversible interactions. A total of 61 strains, consisting of all of the A. viscosus isolates and 86% of the A. naeslundii isolates, coaggregated; 87% inhibited lactose-reversible coaggregation. On the basis of this property and the altered ability of strains to coaggregate after heat treatment of the cells, we delineated four coaggregation groups. The other 13% of the strains constituted a fifth group, which was characterized by a pattern of closely related interactions that were not reversed by lactose. Compared with previously characterized coaggregation properties determined with stock culture strains of actinomycetes, more than 80% of these fresh isolates exhibited identical coaggregation properties. Thus, most of the coaggregation between freshly isolated oral actinomycetes and streptococci involves lactose-reversible cell-cell interactions, which suggests that such coaggregation is mediated by a network of lectin-carbohydrate interactions between complementary cell surface structures on the two cell types.

Actinomyces↗
PubMed1992

Differences in the binding specificities of Pseudomonas aeruginosa M35 and Escherichia coli C600 for lipid-linked oligosaccharides with lactose-related core regions.

Membrane glycolipids contain the lactose sequence (galactose linked to glucose), and the oligosaccharide is variously extended such that there is a cell-type-specific repertoire. In this study, binding of Pseudomonas aeruginosa M35 to lipid-linked lactose (Gal beta 1-4Glc [structure 1]), lacto-N-neotetraose (Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc [structure 2]), lacto-N-tetraose (Gal beta 1-3GlcNAc beta 1-3Gal beta 1-4Glc [structure 3]), and asialo GM1 (Gal beta 1-3GalNAc beta 1-4Gal beta 1-4Glc [structure 4]) was evaluated and compared with binding of Escherichia coli C600 to these compounds. Oligosaccharides were linked to the lipid phosphatidylethanolamine dipalmitoate, and the resulting neoglycolipids were resolved on thin-layer chromatograms or coated onto plastic microtiter wells. Lipid-linked structures 1 to 4 were bound by P. aeruginosa and E. coli in the chromatogram assay, but only structure 4 was bound in the microtiter well assay. As shown previously for E. coli binding to lipid-linked structures 1 to 3, binding to lipid-linked structure 4 was not inhibited with oligosaccharide, indicating a requirement for lipid and oligosaccharide. With few exceptions, sialylation and fucosylation of structures 1 to 4 resulted in impaired or abolished binding. Comparisons of binding intensities in the chromatogram assay indicated that recognition by P. aeruginosa and recognition by E. coli are not identical. Presence of the additional disaccharide unit, as in structure 2, resulted in enhanced binding of P. aeruginosa but diminished binding of E. coli relative to lactose binding; fucosylation at galactose of lactose resulted in markedly diminished binding of P. aeruginosa only. In the microtiter well assay, binding of E. coli to asialo GM1 was much weaker than P. aeruginosa binding. The saccharide-plus-lipid-dependent adhesion may be an important factor in increased susceptibility to infection of epithelia already damaged by microbial and chemical agents; the differing strengths of adhesion to the structural variants may relate to tissue tropism.

Bacterial Adhesion↗
PubMed1977

Analysis of genetic recombination between two partially deleted lactose operons of Escherichia coli K-12.

Genetic recombination between a nontandem duplication of two partially deleted lactose operons (lacMS286phi80dIIlacBK1) in Escherichia coli K-12 has been examined. Since the deletions were nonoverlapping, rare lactose-fermenting (Lac+) recombinants occurred and were detected qualitatively on lactose tetrazolium agar indicator plates as white papillae growing on the surface of red colonies or quantitively on lactose minimal agar plates. Formation of Lac+ recombinants required the recA, recB, and recC gene products. Indirect suppression of recB21 by sbcB15 led to an increase in the frequency of Lac+ recombinants over wild-type levels. recF143 did not appreciably alter the number of Lac+ progeny, whereas recL152 and sbcB15 strains yielded increased numbers of Lac+ recombinants. The nature and formation of Lac+ recombinants was also examined. Respreading analysis indicated that formation of recombinants occurred primarily as the cells entered early stationary phase on the surface of the minimal agar plates and that over 90% of the recombinants contained a phi80dIIlac+ prophage. Time-of-entry experiments suggested that the region of deoxyribonucleic acid between the two operons was not inverted as a result of the recombinational event.

Conjugation, Genetic↗
PubMed1983

Plasmid linkage of the D-tagatose 6-phosphate pathway in Streptococcus lactis: effect on lactose and galactose metabolism.

The three enzymes of the D-tagatose 6-phosphate pathway (galactose 6-phosphate isomerase, D-tagatose 6-phosphate kinase, and tagatose 1,6-diphosphate aldolase) were absent in lactose-negative (Lac-) derivatives of Streptococcus lactis C10, H1, and 133 grown on galactose. The lactose phosphoenolpyruvate-dependent phosphotransferase system and phospho-beta-galactosidase activities were also absent in Lac- derivatives of strains H1 and 133 and were low (possibly absent) in C10 Lac-. In all three Lac- derivatives, low galactose phosphotransferase system activity was found. On galactose, Lac- derivatives grew more slowly (presumably using the Leloir pathway) than the wild-type strains and accumulated high intracellular concentrations of galactose 6-phosphate (up to 49 mM); no intracellular tagatose 1,6-diphosphate was detected. The data suggest that the Lac phenotype is plasmid linked in the three strains studied, with the evidence being more substantial for strain H1. A Lac- derivative of H1 contained a single plasmid (33 megadaltons) which was absent from the Lac- mutant. We suggest that the genes linked to the lactose plasmid in S. lactis are more numerous than previously envisaged, coding for all of the enzymes involved in lactose metabolism from initial transport to the formation of triose phosphates via the D-tagatose 6-phosphate pathway.

Aldehyde-Lyases↗
PubMed1996

Involvement of the central loop of the lactose permease of Escherichia coli in its allosteric regulation by the glucose-specific enzyme IIA of the phosphoenolpyruvate-dependent phosphotransferase system.

Allosteric regulation of several sugar transport systems such as those specific for lactose, maltose and melibiose in Escherichia coli (inducer exclusion) is mediated by the glucose-specific enzyme IIA (IIAGlc) of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). Deletion mutations in the cytoplasmic N and C termini of the lactose permease protein, LacY, and replacement of all cysteine residues in LacY with other residues did not prevent IIAGlc-mediated inhibition of lactose uptake, but several point and insertional mutations in the central cytoplasmic loop of this permease abolished transport regulation and IIAGlc binding. The results substantiate the conclusion that regulation of the lactose permease in E. coli by the PTS is mediated by a primary interaction of IIAGlc with the central cytoplasmic loop of the permease.

Allosteric Regulation↗
PubMed1999

Elements involved in catabolite repression and substrate induction of the lactose operon in Lactobacillus casei.

In Lactobacillus casei ATCC 393, the chromosomally encoded lactose operon, lacTEGF, encodes an antiterminator protein (LacT), lactose-specific phosphoenolpyruvate-dependent phosphotransferase system (PTS) elements (LacE and LacF), and a phospho-beta-galactosidase. lacT, lacE, and lacF mutant strains were constructed by double crossover. The lacT strain displayed constitutive termination at a ribonucleic antiterminator (RAT) site, whereas lacE and lacF mutants showed an inducer-independent antiterminator activity, as shown analysis of enzyme activity obtained from transcriptional fusions of lac promoter (lacp) and lacpDeltaRAT with the Escherichia coli gusA gene in the different lac mutants. These results strongly suggest that in vivo under noninducing conditions, the lactose-specific PTS elements negatively modulate LacT activity. Northern blot analysis detected a 100-nucleotide transcript starting at the transcription start site and ending a consensus RAT sequence and terminator region. In a ccpA mutant, transcription initiation was derepressed but no elongation through the terminator was observed in the presence of glucose and the inducing sugar, lactose. Full expression of lacTEGF was found only in a man ccpA double mutant, indicating that PTS elements are involved in the CcpA-independent catabolite repression mechanism probably via LacT.

Bacterial Proteins↗
PubMed2000

Cloning and characterization of sialidases with 2-6' and 2-3' sialyl lactose specificity from Pasteurella multocida.

Pasteurella multocida is a mucosal pathogen that colonizes the respiratory system of susceptible hosts. Most isolates of P. multocida produce sialidase activity, which may contribute to colonization of the respiratory tract or the production of lesions in an active infection. We have cloned and sequenced a sialidase gene, nanH, from a fowl cholera isolate of P. multocida. Sequence analysis of NanH revealed that it exhibited significant amino acid sequence homology with many microbial sialidases. Insertional inactivation of nanH resulted in a mutant strain that was not deficient in sialidase production. However, this mutant exhibited reduced enzyme activity and growth rate on 2-3' sialyl lactose compared to the wild type. Subsequently, we demonstrated the presence of two sialidases by cloning another sialidase gene that differed from nanH in DNA sequence and substrate specificity. NanB demonstrated activity on both 2-3' and 2-6' sialyl lactose, while NanH demonstrated activity only on 2-3' sialyl lactose. Neither enzyme liberated sialic acid from colominic acid (2-8' sialyl lactose). Recombinant E. coli containing the sialidase genes were able to utilize several sialoconjugants when they were provided as sole carbon sources in minimal medium. These data suggest that sialidases have a nutritional function and may contribute to the ability of P. multocida to colonize and persist on vertebrate mucosal surfaces.

Amino Acid Sequence↗
PubMed2000

Characterization of SotA and SotB, two Erwinia chrysanthemi proteins which modify isopropyl-beta-D-thiogalactopyranoside and lactose induction of the Escherichia coli lac promoter.

The expression, in Escherichia coli, of variants of the Erwinia chrysanthemi secretion genes outB and outS under the Ptac promoter is toxic to the cells. During attempts to clone E. chrysanthemi genes able to suppress this toxicity, I identified two genes, sotA and sotB, whose products are able to reduce the isopropyl-beta-D-thiogalactopyranoside (IPTG) induction of the E. coli lac promoter. SotA and SotB belong to two different families of the major facilitator superfamily. SotA is a member of the sugar efflux transporter family, while SotB belongs to the multidrug efflux family. The results presented here suggest that SotA and SotB are sugar efflux pumps. SotA reduces the intracellular concentration of IPTG, lactose, and arabinose. SotB reduces the concentration of IPTG, lactose, and melibiose. Expression of sotA and sotB is not regulated by their substrates, but sotA is activated by the cyclic AMP receptor protein (CRP), while sotB is repressed by CRP. Lactose is weakly toxic for E. chrysanthemi. This toxicity is increased in a sotB mutant which cannot efficiently efflux lactose. This first evidence for a physiological role of sugar efflux proteins suggests that their function could be to reduce the intracellular concentration of toxic sugars or sugar metabolites.

Bacterial Outer Membrane Proteins↗
PubMed1980

Lactose-positive Vibrio in seawater: a cause of pneumonia and septicemia in a drowning victim.

Lactose-positive Vibrio is a recently recognized marine organism that has pathogenic potential for humans. An organism was isolated from the sputum and blood of a man who was resuscitated after drowning in the sea. The isolates from both sources had the characteristics of lactose-positive Vibrio, which include positive oxidase, citrate, indole, and o-nitrophenyl-beta-D-galactopyranoside reactions and negative Voges-Proskauer, urease, and sucrose reactions. Seawater samples from 21 sites around Galveston Island were cultured for lactose-positive Vibrio over a period of 4 weeks, and 36% of the samples yielded the organism. The environmental isolates were very similar to the clinical isolates in biochemical reactions and susceptibility to antimicrobial agents. The results indicate that lactose-positive Vibrio is a common organism in the marine environment and that it should be considered in the diagnosis of infections, including pneumonia, associated with exposure to the sea.

Adult↗
PubMed1975

"Added lactose" and "added sucrose" cow's milk formulae in nutrition of low birthweight babies.

During the manufacture of dried milks for infant feeding the composition of cow's milk may be modified by the addition of extra carbohydrate powder to lower the relative proportions of protein and minerals, and in practice various carbohydrates are used in a largely empirical manner. In other circumstances it is known that the quality of dietary carbohydrate affects intestinal tolerance, deposition of body fat (in rats), and concentrations of plasma lipids (in man). Therefore, in this study the effects of feeding newborn infants on added lactose formula and added sucrose formula have been investigated. 29 low birthweight babies were observed throughout the first 3 months of life. The added carbohydrate achieved a satisfactory composition in terms of mineral and protein concentration of the reconstituted milk, but the "added lactose" group experienced more diarrhoea and a greater degree of metabolic acidosis during the first week of life. The added lactose group was slightly fatter and the plasma triglyceride concentration slightly higher than in the "added sucrose" group. Despite teleological evidence in favour of lactose, we found no objective contraindication to the addition of sucrose to cow's milk in the manufacture of infant feeding formulae. Both milks contained only small quantities of linoleic acid and the polyunsaturated fatty acid content of the plasma and adipose tissue lipids fell to low levels, but no clinical evidence of "essential fatty acid deficiency" was found.

Acidosis↗
PubMed1996

Lactose absorption in patients with glucose 6-phosphate dehydrogenase deficiency with and without favism.

BACKGROUND: It has recently been suggested that primary lactase deficiency might have been selected for by malaria, as has been previously shown to occur for thalasaemia and glucose 6-phosphate dehydrogenase (G6PD) deficiency. AIMS: To test this hypothesis, the prevalence of primary lactase deficiency in G6PD deficient subjects and in controls from the area of Sassari (Northern Sardinia) was determined, which in the past was characterised by an intermediate malarial endemicity. SUBJECTS: 70 adult subjects with G6PD deficiency, 34 of whom had a past history of favism, and 50 age matched control subjects. METHODS: The capacity to absorb lactose was assessed by measuring breath hydrogen production after oral administration of lactose (50 g) by a gas chromatographic method. RESULTS: Twenty per cent of G6PD deficient subjects with a positive history of favism and 22% of G6PD deficient subjects without a positive history of favism were lactose absorbers compared with 14% lactose absorbers in the control group. The differences were not statistically significant. CONCLUSIONS: These data show that the prevalence of primary lactase deficiency in the area of Sassari is relatively high, but comparable to that seen in the adult population from another area of southern Italy (Naples) where malaria was less endemic.

Adult↗
PubMed1987

Dependency of lactose absorption on lactase activity in starved rats.

The effects of starvation on intestinal disaccharidase activities and disaccharide absorption were studied in rats. Adult male rats were starved for either 16 or 72 h and the specific activity of lactase and sucrase was determined together with the absorption of lactose, sucrose, and glucose in vitro by the everted sac technique. The specific activity of lactase was significantly higher and the specific activity of sucrase was lower in the 72-h starved animals when compared with the 16-h starved group. The higher specific lactase activity in the 72-h starved animals was reflected in enhanced absorption of lactose as determined by the transfer of the constituent monosaccharides into the serosal fluid. The transfer of glucose into the serosal fluid by the glucose sac was also higher in the 72-h starved rats but not to the same extent as that of lactose. The absorption of sucrose was not significantly different between the two groups of animals. This study shows that the increase of intestinal lactase activity induced by starvation of adult rats correlates with in vitro increased lactose absorption.

Animals↗