Decline in measles mortality: nutrition,age at infection,or exposure?

The mortality from measles was studied in an urban area of Guinea-Bissau one year before and five years after the introduction of a vaccination programme. The years after the introduction of immunisation saw a decline in mortality among unvaccinated children with measles. This decline occurred despite a lower age at infection and an increasing prevalence of malnourished children. State of nutrition (weight for age) did not affect the outcome of measles infection. The incidence of isolated cases, however, increased in the period after the introduction of measles vaccination. As mortality was lower among these cases, diminished clustering explained some of the reduction in mortality. Comparison between the urban district and a rural area inhabited by the same ethnic group showed a lower age at infection, less clustering of cases, and lower case fatality ratios in the urban area.Endemic transmission of measles in urban districts leads to less clustering of cases, which may help explain the usually lower case fatality ratios in these areas. As measles vaccination increases herd immunity and diminishes clustering of cases, it may reduce mortality even among unvaccinated children who contract the disease.     

Floral scent in dioeciousSalix (Salicaceae)—a cue determining the pollination system?

Floral scents of male and female inflorescences of three dioeciousSalix species were collected by head-space adsorption, and analysed by GC-MS. InSalix caprea andS. cinerea 1,4-dimethoxy benzene was the main compound, and male and female scents showed a high degree of resemblance. No dominant compound was found inS. repens and malefemale scent similarity was low. Floral scent inSalix is likely a strong orientation cue, guiding pollinators between male and female plants ensuring pollen transfer and pollination. We suggest that a high degree of male-female floral scent resemblance is coupled to a high degree of insect pollination. Floral scent does not promote reproductive isolation betweenS. caprea andS. cinerea.     

Iodoazomycin riboside (1-(5'-iodo-5'-deoxyribofuranosyl)-2-nitroimidazole), a hypoxic cell marker. I. Synthesis and in vitro characterization

Misonidazole (MISO), a selective radiosensitizer of hypoxic cells, forms adducts with cellular biomolecules with rates which are 30-50 X higher under hypoxic as compared to aerobic conditions of incubation. This technique of sensitizer adduct formation was proposed as a possible means of measuring the hypoxic fraction of solid tumors by noninvasive procedures. Iodoazomycin riboside (5'-IAZR) and 5'-[125I]AZR were synthesized and chemically characterized. Measurements of in vitro cytotoxicity and radiosensitizing ability with EMT-6 tumor cells in vitro indicated that 5'-IAZR is approximately 3 X more toxic and effective than is azomycin riboside (AZR) and approximately 10 X more toxic and effective than is MISO. 5'-[125I]AZR was shown to selectively bind to hypoxic EMT-6 cells at rates which were 2.5-3 X faster than those of MISO. The absolute rates of binding of 5'-IAZR to hypoxic cells at concentrations of 10-100 microM are the highest observed in this laboratory for any hypoxic cell radiosensitizer tested to date. These data suggest that 5'-IAZR, when labeled with an appropriate radioisotope (e.g., 131I), might be a useful marker for hypoxic cells in solid tumors amenable to noninvasive detection. Additional studies with animal tumor models appear to be warranted.     

Floral scent variation in the Pyrola rotundifolia complex in Scandinavia and Western Greenland

The variation in floral scent composition within and among populations of four taxa belonging to the Pyrola rotundifolia complex was analyzed using Principal Component Analysis. Two major groups were recognized, P. norvegica and P. grandiflora on the one side and P. rotundifolia s. str. on the other. Benzaldehyde dominated the scent of the first group and methoxy benzenes and phenyl propanoids that of the second group. A large variation in the floral scent chemistry was found both within some of the studied populations as well as among them. The floral scent composition of P. rotundifolia ssp. maritima was no more different from P. rotundifolia ssp. rotundifolia , than the differences between populations of P. rotundifolia ssp. rotundifolia . The findings are in partial agreement with the current delimitation of the taxa in the P. rotundifolia complex.     

Substrate-enzyme interactions and catalytic mechanism in phospholipase C: a molecular modeling study using the GRID program.

Based on the high-resolution X-ray crystallographic structure of phospholipase C from Bacillus cereus, the orientation of the phosphatidylcholine substrate in the active site of the enzyme is proposed. The proposal is based on extensive calculations using the GRID program and molecular mechanics geometry relaxations. The substrate model has been constructed by successively placing phosphate, choline and diacylglycerol moieties in the positions indicated from GRID calculations. On the basis of the resulting orientation of a complete phosphatidylcholine molecule, we propose a mechanism for the hydrolysis of the substrate.     

Reactive oxygen species are important mediators of taurine release from skeletal muscle cells

The present study illustrates elements ofthe signal cascades involved in the activation of taurine effluxpathways in myotubes derived from skeletal muscle cells. Exposingprimary skeletal muscle cells, loaded with ¹⁴C-taurine, to1) hypotonic media, 2) the phospholipaseA₂ (PLA₂) activator melittin, 3)anoxia, or 4) lysophosphatidyl choline (LPC) causes anincrease in ¹⁴C-taurine release and a concomitantproduction of reactive oxygen species (ROS). The antioxidants butulatedhydroxy toluene and vitamin E inhibit the taurine efflux after cellswelling, anoxia, and addition of LPC. The muscle cells possess twoseparate taurine efflux pathways, i.e., a swelling- andmelittin-induced pathway that requires 5-lipoxygenase activity foractivation and a LPC-induced pathway. The two pathways aredistinguished by their opposing sensitivity toward the anion channelblocker DIDS and cholesterol. These data provide evidence forPLA₂ products and ROS as key mediators of the signalcascade leading to taurine efflux in muscle.

     

Large differences in erythrocyte stability between species reflect different antioxidative defense mechanisms

We have developed a screening assay for erythrocyte stability, which is rapid, easy, inexpensive, robust, and suitable for handling a large number of samples in parallel. Erythrocytes are incubated overnight in 96-well microtiter plates in absence or presence of various oxidants, intact cells are pelleted by centrifugation, and lysis is determined by release of intracellular constituents into the supernatant as either activity of lactate dehydrogenase (LDH) or absorbance of hemoglobin at 406 nm. There is good correlation between the methods. A number of advantages by the present method are that only small amounts of blood is needed, washing is optional, erythrocytes may be stored for at least one day before assay, and large numbers of samples can be handled in parallel. Using this set-up, we have compared erythrocyte stability from several different animal species. We find that erythrocyte susceptibility towards lysis induced by H₂O₂ and 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) is highly species dependent. The different susceptibility between species is due to cellular components, since swapping of plasma between species has little or no effect. As a novel observation, we find that erythrocytes from chicken are the most sensitive of the species tested towards lysis by H₂O₂ and are almost four orders of magnitude more sensitive than erythrocytes from man. This is due to a much lower content of catalase in erythrocytes from chicken. A more narrow range is observed for susceptibility towards AAPH and the ranking between the species is different. Thus, chicken erythrocytes are more resistant towards AAPH than some mammals by up to two orders of magnitude. This differential stability towards different oxidative stressors is likely due to evolution/selection of different defense mechanisms.     

Analysis of mannose selection used for transformation of sugar beet

Various factors affecting mannose selection for the production of transgenic plants were studied using Agrobacterium tumefaciens-mediated transformation of sugar beet (Beta vulgaris L.) cotyledonary explants. The selection system is based on the Escherichia coli phosphomannose isomerase (PMI) gene as selectable gene and mannose as selective agent. Transformation frequencies were about 10-fold higher than for kanamycin selection but were only obtained at low selection pressures (1.0–1.5 g/l mannose) where 20–30% of the explants produced shoots. The non-transgenic shoots were eliminated during the selection procedure by a stepwise increase in the mannose concentration up to 10 g/l. Analysis of the transformed shoots showed that the PMI activity varied from 2.4 mU/mg to 350 mU/mg but the expression level was independent of the selection pressure. Complete resistance to mannose of transformed shoots was observed already at low PMI activities (7.5 mU/mg). Genomic DNA blot analysis confirmed the presence of the PMI gene in all transformants analysed. The possible mode of action of mannose selection compared to other selection methods is discussed.     

Inactivation of Vibrio anguillarum by Attached and Planktonic Roseobacter Cells

The purpose of the present study was to investigate the inhibition of Vibrio by Roseobacter in a combined liquid-surface system. Exposure of Vibrio anguillarum to surface-attached roseobacters (10⁷ CFU/cm²) resulted in significant reduction or complete killing of the pathogen inoculated at 10² to 10⁴ CFU/ml. The effect was likely associated with the production of tropodithietic acid (TDA), as a TDA-negative mutant did not affect survival or growth of V. anguillarum.Antagonistic interactions among marine bacteria are well documented, and secretion of antagonistic compounds is common among bacteria that colonize particles or surfaces (8, 13, 16, 21, 31). These marine bacteria may be interesting as sources for new antimicrobial drugs or as probiotic bacteria for aquaculture.Aquaculture is a rapidly growing sector, but outbreaks of bacterial diseases are a limiting factor and pose a threat, especially to young fish and invertebrates that cannot be vaccinated. Because regular or prophylactic administration of antibiotics must be avoided, probiotic bacteria are considered an alternative (9, 18, 34, 38, 39, 40). Several microorganisms have been able to reduce bacterial diseases in challenge trials with fish or fish larvae (14, 24, 25, 27, 33, 37, 39, 40). One example is Phaeobacter strain 27-4 (17), which inhibits Vibrio anguillarum and reduces mortality in turbot larvae (27). The antagonism of Phaeobacter 27-4 and the closely related Phaeobacter inhibens is due mainly to the sulfur-containing tropolone derivative tropodithietic acid (TDA) (2, 5), which is also produced by other Phaeobacter strains and Ruegeria mobilis (28). Phaeobacter and Ruegeria strains or their DNA has been commonly found in marine larva-rearing sites (6, 17, 28).Phaeobacter and Ruegeria (Alphaproteobacteria, Roseobacter clade) are efficient surface colonizers (7, 11, 31, 36). They are abundant in coastal and eutrophic zones and are often associated with algae (3, 7, 41). Surface-attached Phaeobacter bacteria may play an important role in determining the species composition of an emerging biofilm, as even low densities of attached Phaeobacter strain SK2.10 bacteria can prevent other marine organisms from colonizing solid surfaces (30, 32).In continuation of the previous research on roseobacters as aquaculture probiotics, the purpose of this study was to determine the antagonistic potential of Phaeobacter and Ruegeria against Vibrio anguillarum in liquid systems that mimic a larva-rearing environment. Since production of TDA in liquid marine broth appears to be highest when roseobacters form an air-liquid biofilm (5), we addressed whether they could be applied as biofilms on solid surfaces.