Detection of bacteriocins of lactic acid bacteria isolated from foods and comparison with pediocin and nisin

A total of 663,533 colonies from 72 dairy and meat sources showed a detection rate of 0.2% for bacteriocin producers using direct plating techniques. A further 83,000 colonies from 40 fish and vegetable sources showed a detection rate of 3.4% for bacteriocin producers using selective enrichment procedures. A collection of seven purified isolates showing a different host spectrum of bacteriocin activity and with the ability to produce bacteriocins in broth culture were compared with nisin and pediocin (with respect to their inhibitory activity, determined by the critical dilution method), against various indicator bacteria in agar and broth. The sensitivity of Listeria species to various bacteriocins was influenced by the agar and broth test systems used. A Lactobacillus curvatus strain was found to be the most suitable indicator for quantitating antimicrobial effects of all the bacteriocins investigated in both agar and broth test systems. The bacteriocin-producing isolates were characterized by biochemical reactions and DNA restriction enzyme profiles and taxonomic identification revealed species of Lactobacillus, Carnobacterium and Lactococcus assigned on the basis of 16S rDNA sequences.     

Mechanistic action of pediocin and nisin: recent progress and unresolved questions

BACKGROUND: Present knowledge of mechanisms involved in human fertilization has uncovered a new group of pathologic conditions that have been generically named fertilization abnormalities. AIM: To determine the contribution of chromosomal alterations to in vitro fertilization failures. MATERIALS AND METHODS: A cytogenetic analysis of oocytes that were not fertilized after insemination with normal spermatozoa. Oocytes were obtained from patients subjected to in vitro fertilization in a public hospital of Metropolitan Santiago. Ovulation was induced in these patients administering GnRh-a, FSH, HMG and HCG. The double fixation technique described by Wramsby was used to obtain chromosomes. RESULTS: One hundred and seven oocytes coming from 45 women aged 25 to 42 years old were studied. The frequency of aneuploidy in these oocytes was 37.3%, with a 11.8% of hypohaploidy, a 21.6% of hyperhaploidy and a 3.9% of diploid oocytes. In hyperhaploid as well as in hypohaploid oocytes, the chromosomes involved in aneuploidy pertained to groups D. and G. CONCLUSIONS: Although the total frequency of aneuploidy is within normal ranges, the frequency of hyperhaploidy is superior to previous reports. An explanation for this finding could be that the occurrence of a lack of disjunction with chromosomal retention in the parental cell occurs with a higher frequency than that in which the chromosomes are retained in the polocyte. We also suggest that oocyte chromosomal aneuploidy could contribute to the failure of in vitro fertilization procedures.     

Partial purification and characterisation of sugarcane neutral invertase

Sugarcane neutral invertase (SNI) has been partially purified from mature sugarcane stem tissue to remove any potential competing activity. The enzyme is non-glycosylated and exhibits catalytic activity as a monomer, dimer and tetramer, most of the activity elutes as a monomer of native M(r) ca 60 k. The enzyme displays typical hyperbolic saturation kinetics for Suc hydrolysis. It has a K(m) of 9.8 mM for Suc and a pH optimum of 7.2. An Arrhenius plot shows the energy of activation of the enzyme for Suc to be 62.5 kJ mol-1 below 30 degrees and -11.6 kJ mol-1 above 30 degrees. SNI is inhibited by its products, with Fru being a more effective inhibitor than Glc. SNI is significantly inhibited by HgCl2, AgNO3, ZnCl2, CuSO4 and CoCl2 but not by CaCl2, MgCl2 or MnCl2. SNI showed no significant hydrolysis of cellobiose or trehalose.     

Development and comparison of iron dextran products

Slowly replicating, species-specific and complex DNA viruses, such as cytomegaloviruses (CMVs), which code for > 200 antigenic proteins, should be easy prey to the host's immune system. Yet, CMVs are amazingly adapted opportunists that cope with multiple immune responses. Frequently, CMVs exploit immune mechanisms generated by the host. These strategies secure the persistence of CMVs and provide opportunities to spread to naive individuals.     

On-line PO2 and PN2O analysis with an in vivo catheter electrode

A technique was developed for the in vivo determination of PO2 and PN2O with a catheter electrode using double-pulse polarography. The method was evaluated in dog studies comparing readings from the electrode with those from a mass spectrometer employing an in vivo probe. The oxygen readings obtained from the catheter electrode were also compared with values obtained by conventional blood-gas analysis. Good agreement was observed between the electrode and the mass spectrometer for both PO2 and PN2O. Similar agreement was found between the electrode readings and blood-gas analysis for PO2. In the presence of halothane, the electrode over-read for both PO2 and PN2O; a remedy is suggested. The in vivo electrode provides an effective, less expensive, alternative to the mass spectrometer for the on-line measurement of PO2 and PN2O in vivo.     

Structural characterisation and comparison of the native and A-states of equine lysozyme

Native state 1H NMR resonance assignments for 125 of the 129 residues of equine lysozyme have enabled measurement of the hydrogen exchange kinetics for over 60 backbone amide and three tryptophan indole hydrogen atoms in the native state. Native holo equine lysozyme hydrogen exchange protection factors are as large as 10(6), the most protected residues being located in elements of secondary structure. High exchange protection in the domain interface correlates with the binding of Ca2+ in this region. Equine lysozyme differs from most non-Ca2+ binding lysozymes in forming a highly populated partially folded state at low pH. The protein in this A-state at pH 2.0 has been found to bind 1-anilino-naphthalene-8-sulphonate with the enhancement of fluorescent intensity and blue shift in the spectral maximum characteristic of molten globules. NMR spectra indicate that the A-state is globally much less ordered than native equine lysozyme but does not contain significant regions of random coil structure. The amides most protected against hydrogen exchange in the A-state (protection factors up to 10(2) at 5 degrees C) correspond to residues of three of the four alpha-helices of the native state; the side-chains of these residues form a hydrophobic cluster that includes five aromatic residues. Circular dichroism and tryptophan fluorescence indicate that these residues are substantially more constrained than similar residues in "classical" molten globules. Taken together, the data suggest a model for the A-state of equine lysozyme in which a more ordered core is surrounded by a less ordered but still compact polypeptide chain.     

Partial characterization of the cohemolytic factor produced by Streptococcus uberis and comparison with the CAMP-factor

Exosubstances (cohemolysins) produced by Streptococcus agalactiae (CAMP-factor) and Streptococcus uberis (Uberis-factor) showing hemolytic synergism with beta-lysin produced by Staphylococcus aureus were compared. Cohemolytic activity was evaluated in the supernatants of bacterial cultures, before and after ammonium sulfate precipitation. Sheep erythrocytes sensitized with beta-lysin were used as substrate. The assays were performed in microtiter plates and results were expressed as cohemolytic units/ml. Maximum cohemolytic activity was detected, respectively, after 8 h and 14 h of growth in Columbia broth in S. uberis and S. agalactiae cultures. Cohemolytic activities of both microorganisms showed similarities when submitted to various physical and chemical treatments. They were significantly decreased by heating at 60 degrees C and 100 degrees C, or in presence of trypsin, and were abolished in the presence of Tween 20. Activities were found to be stable in crude supernatants and concentrated preparations maintained at -20 degrees C for 3 months. Differences were related to levels of activity and kinetics of detection during the growth cycle. The results indicate the proteic nature, at least in part, of the Uberis factor. Analysis by PAGE in the presence or absence of SDS allowed us to correlate Uberis activity with a protein band with apparent molecular mass of 42 kDa, while CAMP activity was associated with a protein band of 27 kDa.     

Al5Ti1B中间合金细化剂研制及同类产品对比

利用氟盐铝热反应法制备了Al5Ti1B中间合金细化剂,制定出完整的工艺路线和参数,并对其反应过程和原理进行了分析.制取的中间合金化学成分(质量分数)为:Ti,4.64%;B,0.84%.通过与荷兰KBM、英国LSM、国内某厂生产的同类产品进行化学成分、微观组织和细化效果三项指标对比分析,结果表明:自行开发的中间合金细化剂质量优于国内同类产品;同等条件下细化效果(TiAl₃<50μm,TiB₂<1μm)与KBM公司的同类产品接近,达到进口同类产品水平.     

PO2 in the carotid body perfused and/or superfused with cell-free media

We measured with a micro-O2 electrode the tissue PO2 (PtO2) in the cat carotid body (CB) to see whether it was adequately oxygenated when perfused or superfused with artificial, cell-free (c-f) solutions (pH = 7.4; temp = 35-38 degrees C). To obtain a relative measure of O2 consumption (VO2), we also measured the rate of disappearance of O2 following stoppage of the blood flow, and compared these disappearance curves with those during stoppage of the c-f perfusion solutions. In 14 cats normal (blood perfusion) PtO2 values ranged from 10 to 104 mmHG; chi = 72 +/- 4 (SE--as used throughout). During 3 h of c-f perfusion with air-equilibrated Locke's solution, PtO2 ranged from 62 to about 160 mmHg; chi = 133 +/- 4. When perfused with Fay's equilibrated with 98% O2-2% CO2 no PtO2 values in the CB were below 300 mmHg (4 cats). In eight additional cats the CB was cleared of blood then superfused with saline equilibrated with 50% O2 underneath and air-equilibrated saline over. Less than 5% of the PtO2 values found were below 5 mmHg. We conclude that most studies on the artificially perfused or superfused CB cannot be invalidated on the basis that the preparations were hypoxic. O2 disappearance curves taken during blood perfusion were significantly faster than during c-f perfusion indicating a marked reduction in VO2 with c-f perfusion.     

Partial sequencing of hog cholera virus Alfort strain genome and its comparison with other pestivirus strains

After molecular RNA cloning of the Alfort strain (Alfort/LCRV) of hog cholera virus (HCV), the nucleotide sequence of about 70% of the total genome was determined. This sequence was compared with homologous parts of previously published pestivirus genomes. The average homology with another clone of the Alfort strain (Alfort/FRC) was found to be lower (86.1%) than with Brescia strain of HCV (94.3%), while, compared with NADL, Osloss and SD-1 (3 different strains of bovine viral diarrhea virus, BVDV), the average homology was 67%. Although the amino-acid sequences show a higher degree of conservation, they had a similar degree of homology (92.7, 96.7, 69, 68.2 and 69%, respectively). Partial sequence comparison also revealed that Alfort/LCRV strain was more closely related to Alfort 187 (98.6% for the nucleotides and amino acids) and Weybridge (97.3% for the nucleotides and 96.1% for the amino acids) strains of HCV than it was to Alfort/FRC. These results may indicate that the Alfort/FRC strain has undergone more genomic variations during its historical passage. Genomic relationships among the pestiviruses are discussed.     

Effects of routine hyperventilation on PCO2 and PO2 in normal subjects: implications for EEG interpretations

There are few data in the EEG literature describing the time course of hyperventilation-(HV) induced changes in blood gases, despite this being a routine activating procedure. We studied changes in blood gases and EEG in nine normal adult subjects before, during, and after HV. The mean PCO2 fell 18 mm Hg from the baseline during HV and recovered in 7 min. The mean PO2 rose 7 mmHg during HV and fell to 25 mm Hg below baseline 5 min after HV. The PCO2 recovery period is longer than is usually assumed in clinical EEG. The PO2 fall to a nadir at 5 min after the end of HV suggests that close attention should be paid to this period, as is confirmed by the re-buildup seen in moyamoya disease. Despite uniform changes in blood gases, the EEG median power frequency change showed marked variability; on average, it dropped by 1 Hz during HV and returned to baseline within 2 min of resumption of normal respiration. The EEG root-mean-square power showed a 200% increase during HV and also had returned to normal within 2 min.     

在磷酸介质中水热合成纳米TiO2光催化剂

使用工业偏钛酸为前驱体，在磷酸介质中借助于水热合成方法，制备了二氧化钛纳米颗粒。通过透射电子显微镜（TEM）、扫描电子显微镜（SEM）、X射线衍射仪（XRD）、光催化活性检测仪等手段对所得的样品的形貌、晶型结构及光催化降解亚甲基蓝的性能进行了研究。结果表明，颗粒的形貌近似球形，所制得的产品均为锐钛矿相，在90℃下得到的纳米二氧化钛颗粒粒径为9nm，随着温度的升高得到的纳米晶粒逐渐变大（约17nm），且所得产品降解亚甲基蓝的能力较强。     

Partial Fourier reconstruction for three-dimensional gradient echo functional MRI: comparison of phase correction methods

Partial Fourier (PF) methods take advantage of data symmetry to allow for either faster image acquisition or increased image resolution. Faster acquisition and increased spatial resolution are advantageous for fMRI because of increased temporal resolution and/or reduced partial volume effects, respectively. Standard PF methods, which use a phase reference obtained from a low resolution image, are adequate for the reconstruction of time-stationary images acquired using either spin echoes or short TE gradient echoes. In fMRI, however, multiple images are acquired using long TE gradient echoes, which introduces possible phase drifts in the fMRI data and high spatial frequencies in the phase reference. This work investigates several techniques developed to reconstruct fMRI data obtained with PF acquisitions. PF methods that account for both high-frequency spatial variations and time-dependent drifts in the phase reference are discussed and are quantitatively evaluated using receiver operator characteristic curve analysis.     

Phosphorescence quenching method for measurement of intracellular PO2 in isolated skeletal muscle fibers

Values of skeletal muscle intracellular PO2 during conditions ranging from rest to maximal metabolic rates have been difficult to quantify. A method for measurement of intracellular PO2 in isolated single skeletal muscle fibers by using O2-dependent quenching of a phosphorescent-O2 probe is described. Intact single skeletal muscle fibers from Xenopus laevis were dissected from the lumbrical muscle and mounted in a glass chamber containing Ringer solution at 20 degreesC. The chamber was placed on the stage of an inverted microscope configured for epi-illumination. A solution containing palladium-meso-tetra (4-carboxyphenyl) porphine bound to bovine serum albumin was injected into single fibers by micropipette pressure injection. Phosphorescence-decay curves (average of 10 rapid flashes) were recorded every 7 s from single cells (n = 24) in which respiration had been eliminated with NaCN, while the PO2 of the Ringer solution surrounding the cell was varied from 0 to 159 Torr. For each measurement, the phosphorescence lifetime was calculated at the varied extracellular PO2 by obtaining a best-fit estimate by using a monoexponential function. The phosphorescence lifetime varied from 40 to 70 microseconds at an extracellular PO2 of 159 Torr to 650-700 microseconds at 0 Torr. The phosphorescent lifetimes for the varied PO2 were used to calculate, by using the Stern-Volmer relationship, the phosphorescence-quenching constant (100 Torr-1. s-1), and the phosphorescence lifetime in a zero-O2 environment (690 microseconds) for the phosphor within the intracellular environment. This technique demonstrates a novel method for determining intracellular PO2 in isolated single skeletal muscle fibers.     

Characteristics of Tn5307 exchange and intergeneric transfer of genes associated with nisin production

Transfer of the Lactococcus lactis 11454 nisin-sucrose conjugative transposon, Tn5307, was investigated to develop a methodology for conjugation of this element to other lactic acid bacteria. Tn5307 exchange was sensitive to temperature and pH but was not affected by protease or amylase treatments to donor cells. Moreover, conjugation studies demonstrated that the direct-plate method could be employed to rapidly identify LM2301 transconjugants able to transfer Tn5307 at least ten times more efficiently than 11454. Intergeneric transfer of nisin and sucrose genes between L. lactis and a dairy Enterococcus sp. was also investigated. Erythromycin-resistant Enterococcus sp. recipients were developed by electro-transformation with pGK13 or by conjugal introduction of the broad-host-range plasmid pAM beta 1. Matings between L. lactis 11454 and an Enterococcus sp. recipient that contained pAM beta 1 yielded sucrose-positive, nisin-immune transconjugants at a frequency of 2.3 x 10(-9) transconjugants per donor cfu. Agar-overlay assays for nisin production revealed that enterococcal transconjugants did not produce the bacteriocin, but DNA.DNA hybridization with a nisA-specific probe demonstrated that these bacteria had acquired the nisin structural gene.     

Studies on purification and some properties of nisin from Lactococcus lactis subsp. lactis Al2

Protoporphyria is a genetic disorder in which patients may develop severe protoporphyrin-induced liver damage and require transplantation. Because unique problems occur in the perioperative period and because excess production of protoporphyrin by the bone marrow continues after liver transplantation, the efficacy of this procedure for protoporphyric liver disease is uncertain. We present follow-up of nine patients who underwent liver transplantation. Two patients died within 2 months of transplantation, one from complications of abdominal bleeding and the other from sepsis after bowel perforations. The remaining seven patients had follow-up at 14 months to 8 years after transplantation (mean, 3.8 years). Two of the seven had suffered skin burns from exposure to operating room lights, which healed without scarring. Three had axonal neuropathies in the postoperative period requiring prolonged mechanical ventilation, and motor defects persisted in two. Five patients had normal liver chemistries at follow-up (mean, 3.5 years), with liver biopsy results normal or showing mild portal triad abnormalities, but erythrocyte protoporphyrin levels remained significantly elevated (1,765 +/- 365 mcg/dL; normal, < 65). The other two patients, both of whom had rejection, cytomegalovirus infection, and biliary tract obstruction requiring endoscopic therapy, had a recurrence of protoporphyric liver disease as indicated by liver biopsy features. One died 5 years after transplantation from complications of the liver disease. The other was stable 3.3 years after transplantation and was being monitored for possible retransplantation. Thus, liver transplantation can be performed successfully in patients with protoporphyric liver disease, with intermediate survival rates comparable to the general transplant population. However, disease may recur in the graft, particularly if there are complications that cause cholestasis.     

Partial purification and characterisation of Bfi57I and Bfi89I, restriction endonucleases from different strains of Butyrivibrio fibrisolvens

The Escherichia coli nucleoid-associated DNA-binding proteins HU and IHF are required for numerous biological processes, including phage growth (e.g., lambda, phi 80, Mu and f1) and DNA replication. Here, we show that growth of T4 phage is inhibited both in hupA hupB and himA himD double mutants. The growth profile of triple mutants (hupA hupB himA and hupA hupB himD) suggests that HimD subunits can form homodimers, which are functionally competent for supporting in vivo growth of phage T4.     

盘条与钢丝国家标准与对应国际标准、国外先进标准的比对分析及对策研究

通过对盘条与钢丝20项具体的国家标准与对应国际标准、国外先进标准的比对分析,提出了盘条与铜丝国际标准研制以及有效应对该领域技术性贸易措施的对策建议。