The β-Hemolysin and Intracellular Survival of Streptococcus agalactiae in Human Macrophages

S. agalactiae (group B streptococci, GBS) is a major microbial pathogen in human neonates and causes invasive infections in pregnant women and immunocompromised individuals. The S. agalactiae β-hemolysin is regarded as an important virulence factor for the development of invasive disease. To examine the role of β-hemolysin in the interaction with professional phagocytes, the THP-1 monocytic cell line and human granulocytes were infected with a serotype Ia S. agalactiae wild type strain and its isogenic nonhemolytic mutant. We could show that the nonhemolytic mutants were able to survive in significantly higher numbers than the hemolytic wild type strain, in THP-1 macrophage-like cells and in assays with human granulocytes. Intracellular bacterial multiplication, however, could not be observed. The hemolytic wild type strain stimulated a significantly higher release of Tumor Necrosis Factor-α than the nonhemolytic mutant in THP-1 cells, while similar levels of the chemokine Interleukin-8 were induced. In order to investigate bacterial mediators of IL-8 release in this setting, purified cell wall preparations from both strains were tested and found to exert a potent proinflammatory stimulus on THP-1 cells. In conclusion, our results indicate that the β-hemolysin has a strong influence on the intracellular survival of S. agalactiae and that a tightly controlled regulation of β-hemolysin expression is required for the successful establishment of S. agalactiae in different host niches.     

Lipoxygenase-generated hydroperoxides account for the nonphysiological features of ethylene formation from 1-aminocyclopropane-1-carboxylic acid by microsomal membranes of carnations

Several lines of evidence indicate that the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene by microsomal membranes from carnation flowers is attributable to hydroperoxides generated by membrane-associated lipoxygenase (EC 1.13.11.12). As the flowers senesce, the capability of isolated microsomal membranes to convert ACC to ethylene changes. This pattern of change, which is distinguishable from that for senescing intact flowers, shows a close temporal correlation with levels of lipid hydroperoxides formed by lipoxygenase in the same membranes. Specific inhibitors of lipoxygenase curtail the formation of lipid hydroperoxides and the production of ethylene from ACC to much the same extent, whereas treatment of microsomes with phospholipase A₂, which generates fatty-acid substrates for lipoxygenase, enhances the production of hydroperoxides as well as the conversion of ACC to ethylene. Lipoxygenase-generated lipid hydroperoxides mediate the conversion of ACC to ethylene in a strictly chemical system and also enhance ethylene production by microsomal membranes. The data collectively indicate that the in-vitro conversion ACC to ethylene by microsomal membranes of carnation flowers is not reflective of the reaction mediated by the native in-situ ethylene-forming enzyme.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EDTA ethylenediaminetetraacetic acid     

Regulation of DNA replication by homopurine/homopyrimidine sequences

The simple repeating homopurine/homopyrimidine sequences dispersed throughout many eukaryotic genomes are known to form triple helical structures comprising three-stranded and single-stranded DNA. Several lines of evidence suggest that these structures influence DNA replication in cells. Homopurine/homopyrimidine sequences cloned into simian virus 40 (SV40) or SV40 origin-containing plasmids caused a reduced rate of DNA synthesis due to the pausing of replication forks. More prominent arrests were observed in in vitro experiments using single-stranded and double-stranded DNA with triplex-forming sequences. Nucleotides unable to form triplexes when present in the template DNA or when incorporated into the nascent strand prevented termination. Similarly, mutations destroying the triplex potential did not cause arrest while compensatory mutations restoring triplex potential restored it. These and other observations from a number of laboratories indicating that homopurine/homopyrimidine sequences act as arrest signals in vitro and as pause sites in vivo during replication fork movement suggest that these naturally occurring sequences play a regulatory role in DNA replication and gene amplification.     

The greenhouse effect: the impacts of carbon dioxide (CO2), ultraviolet-B (UV-B) radiation and ozone (O3) on vegetation (crops)

Man's influence on the greenhouse effect, the heating of the atmosphere due to increasing concentrations of tropospheric trace gases, is of much international concern. Among the climatic variables, elevated levels of carbon dioxide (CO₂), ultraviolet-B (UV-B) radiation and ozone (O₃) are known to have a direct effect on vegetation. Our current knowledge of these effects is mainly based on studies involving single stress mode. Thus, the joint effects of CO₂, UV-B and O₃ on vegetation are poorly understood. Nevertheless, based on the literature analysis of plant response to individual stress factors, it can be concluded that sorghum, pea, bean, potato, oat, lettuce, cucumber, rice and tomato are among the crop species potentially sensitive to the joint effects of the aforementioned three variables. Similar information for tree species is essentially lacking.At least with some climatic variables such as O₃, present modeling efforts of cause-effect relationships have proven to be controversial. While at a regional geographic scale ambient CO₂ concentrations appear to be relatively homogeneous, ambient concentrations of O₃ exhibit significant temporal and spatial variability. Because of the protective action of O₃ against UV-B, similar but inverse temporal and spatial variability is expected in the surface levels of UV-B. Thus, future experimental designs should consider these exposure dynamics and modeling cuase-effect relationships should be directed to stochastic processes.     

Lifelong exercise and stroke.

OBJECTIVES--To examine the potential of lifelong patterns of increased physical activity to prevent stroke. DESIGN--Case-control study. SETTING--11 general practices in west Birmingham. SUBJECTS--125 men and women who had just had their first stroke and were aged 35-74 and 198 controls frequency matched for age and sex recruited over 24 months during 1988-90. Exclusion criteria were a previous history of stroke, mitral valvular heart disease combined with atrial fibrillation, primary or metastatic cerebral neoplasm, or coagulation disorder or myeloproliferative disease. MAIN OUTCOME MEASURES--Odds ratios for stroke related to lifetime history of exercise after 15 years of age. RESULTS--A history of vigorous exercise during the ages 15-25 appeared to protect from stroke: odds ratio adjusted for age and sex 0.33 (95% confidence interval 0.2 to 0.6). This effect was independent of other potential risk factors. Increasing years of participation in vigorous exercise between the ages of 15 and 55 produced an increasing protection from stroke (p < 0.001). In the 65 cases and 169 controls who were free of cardiac ischaemia, peripheral vascular disease, and poor health recent vigorous exercise and walking were protective against stroke: odds ratios of 0.41 (0.2 to 1.0) for recent vigorous exercise and 0.30 (0.1 to 0.7) for recent walking. CONCLUSIONS--Appreciable protection from stroke in later life is conferred by vigorous exercise in early adulthood. This increased level of physical activity should, if possible, be continued lifelong.     

Phospholipid vesicle aggregation induced by human myelin basic protein

Human myelin basic protein isolated from the brains of individuals who died with multiple sclerosis was more potent in inducing the aggregation of egg phosphatidylcholine vesicles than was the basic protein isolated from the brains of normal individuals. The portion of myelin basic protein which bound to egg phosphatidylcholine vesicles was separated from the free protein by sucrose density gradient centrifugation. Similar amounts of basic protein from normal or from multiple sclerosis brains are bound to the lipid and no consistent differences in the N^G, N^G dimethyl-arginine content of the protein fractions have been found.     

Correlation of encystment and division in Schizopyrenus russelli.

Schizopyrenus russelli, a free-living soil ameba, grows and encysts in the presence of bacteria. The encystment occurs with decline in the division rate. This is accompanied by incorporation of [U-14C] glucose into cyst cellulose. The degree of multiplication (but not of encystment) is a function of bacterial concentration. Berenil, a trypanocidal drug, while allowing excystment, completely inhibited multiplication of emerged amebae and their encystment. Addition of this drug after 24 hr, when amebae had gone into a phase of active division failed to check encystment, although it still inhibited further multiplication of the amebae. The findings suggest that a phase of cell division may be a prerequisite for encystment.