An overview of some mechanisms of bacterial pathogenesis

The adherence of microorganisms to host surfaces is highly specific, and in many cases, essential for subsequent pathogenetic events to occur. A dynamic process leading to increased mucosal adherence of gram-negative bacilli to epithelial cell receptors in the oral cavity appears to be the initial step in the development of pneumonia. In infectious processes secondary to Streptococcus pneumoniae, adherence may also play a role in specific syndromes. In many cases, however, colonization of oropharyngeal mucus itself, the presence of capsular polysaccharide, and the release of various cell wall components appear to interact to cause clinical disease. In Neisseria gonorrhoeae infections, adherence is all important and is mediated by a number of cell surface structures. These have been studied extensively. Many of these structures, such as pili and protein II, exhibit great variability both between strains and in the same organism at different stages of infection. Others, such as protein I, are more constant. This information has been used in the production of specific vaccines to more preserved structures to inhibit adherence. These will be tested in the near future. It is our view that a better understanding of the many forms of bacterial adherence will be the key to our designing more effective strategies to detect early infection and to intervene more decisively to limit its spread.     

Interacting forces of predation and fishing affect species’ maturation size

1. Fishing is a strong selective force and is supposed to select for earlier maturation at smaller body size. However, the extent to which fishing‐induced evolution is shaping ecosystems remains debated. This is in part because it is challenging to disentangle fishing from other selective forces (e.g., size‐structured predation and cannibalism) in complex ecosystems undergoing rapid change.
2. Changes in maturation size from fishing and predation have previously been explored with multi‐species physiologically structured models but assumed separation of ecological and evolutionary timescales. To assess the eco‐evolutionary impact of fishing and predation at the same timescale, we developed a stochastic physiologically size‐structured food‐web model, where new phenotypes are introduced randomly through time enabling dynamic simulation of species'' relative maturation sizes under different types of selection pressures.
3. Using the model, we carried out a fully factorial in silico experiment to assess how maturation size would change in the absence and presence of both fishing and predation (including cannibalism). We carried out ten replicate stochastic simulations exposed to all combinations of fishing and predation in a model community of nine interacting fish species ranging in their maximum sizes from 10 g to 100 kg. We visualized and statistically analyzed the results using linear models.
4. The effects of fishing on maturation size depended on whether or not predation was enabled and differed substantially across species. Fishing consistently reduced the maturation sizes of two largest species whether or not predation was enabled and this decrease was seen even at low fishing intensities (F = 0.2 per year). In contrast, the maturation sizes of the three smallest species evolved to become smaller through time but this happened regardless of the levels of predation or fishing. For the four medium‐size species, the effect of fishing was highly variable with more species showing significant and larger fishing effects in the presence of predation.
5. Ultimately our results suggest that the interactive effects of predation and fishing can have marked effects on species'' maturation sizes, but that, at least for the largest species, predation does not counterbalance the evolutionary effect of fishing. Our model also produced relative maturation sizes that are broadly consistent with empirical estimates for many fish species.

     

Location of the isoleucine arrest point in CHO and 3T3 cells

An isoleucine arrest point in G1 was determined by two methods for CHO and 3T3 cells. In the first method the fraction of cells entering S after isoleucine deprivation was assessed by [³H]thymidine labelling and autoradiography. In the second method cells entering S after isoleucine deprivation were identified by double-label autoradiography using [³H] and [¹⁴C]thymidine. From the fraction of cells entering S, determined by the two methods, the arrest point in G1 (and entry into G0) is located within the last 40 min of G1.     

A metabolic switch produced by enzymically interconvertible forms of an enzyme

A system of enzymically interconvertible enzyme forms (interconversion cycle) is known to increase the sensitivity to regulators. Here it is shown that this system may also provide a discrete switching mechanism in which the response is maintained when the stimulus is removed. These switches may be important in producing discontinuous metabolic changes such as those associated with cell differentiation.     

Optimal conditions for breaking medically important yeasts by an inexpensive and simple method

Conditions for breaking various medically important yeasts using glass beads, 30 ml Corex centrifuge tubes, and a Vortex mixer were determined. From 75–95% ofCandida hyphal cells and all species of yeasts exceptSporothrix schenckii were broken when 10 g of 0.45–0.50 mm glass beads, 50–300 mg of wet cells in 5 ml of buffer, and 90 s of vortexing were employed. Yeasts ofSporothrix schenckii broke more efficiently when 0.25–0.30 mm beads were used.     

Maximal oxygen uptake in Danish adolescents 16-19 years of age

A random sample of schoolchildren, 119 boys and 153 girls, was tested in the fall of 1983. The data presented here are anthropometric data (height, weight, fat % and vital capacity) and oxygen uptake directly measured on a bicycle ergometer. The mean height and weight for boys were 179.1 cm and 67.7 kg, and those for girls were 168.0 cm and 59.6 kg. The mean fat content was 9.1% for boys and 19.1% for girls, and their mean vital capacities were 4.91 and 3.61 respectively. The boys had a high maximal oxygen uptake (51.7 ml X kg-1 X min-1) showing no reduction over the age span studied. The girls' maximal oxygen uptake was lower (overall mean 40.0 ml X kg-1 X min-1) with a small reduction from 16 to 19 years of age. When comparing maximal oxygen uptake per kg lean body mass in the two sexes, the boys had 18.4% higher values than the girls, indicating that girls of this age have the lower fitness level. The results of maximal aerobic power measurement in the boys compare well with findings from other investigations using direct measurements, indicating that the fitness of teenage boys is kept at a high level. Comparable data from various countries for girls show different pictures, but it appears that in general they have a low fitness level.     

Metyrapone - reduced cytochrome P-450 complex: A specific method for the determination of the phenobarbital inducible form of rat hepatic microsomal cytochrome P-450

Using homogeneous cytochrome P-450, we have shown that the well-known metyrapone-dithionite reduced cytochrome P-450 complex is specific for the cytochrome P-450b induced by phenobarbital. A linear relationship was observed between the absorbance of metyrapone-reduced cytochrome P-450 complex and the one of CO-reduced cytochrome P-450 complex, the usual method for the determination of cytochrome P-450. A method has been proposed for the specific determination of the cytochrome P-450b.