Effect of biotin antagonists and related substances upon the growth of the coagulase-negative staphylococci

The biotin activity, or anti-biotin properties of a number of substances, wastested on a group of biotin-requiring, coagulase-negative Staphylococcus strains. Of the 18 cultures tested desthiobiotin served as a source of biotin for 17 strains. This substance appeared to be 40 per cent as active as biotin in supporting growth for two of the cultures tested. This substance possessed antibiotin properties for one strain (S19). Homobiotin, one of the chemical homologs of biotin, served as a biotin source for 17 of the 18 strains. Its activity appeared to be less than 0.1 percent of that of biotin among the 8 strains tested. Although it replaced biotin in high concentrations, small quantities appeared to possess anti-biotin properties for one of the Staphylococcus strains. Homobiotin acted as an ariti-biotin substance for strain S36 in all concentrations tested. In contrast 'to studies reported on other biotin-requiring microorganisms, there appeared to be no stoichiometric relationship between biotin and avidin in the nutrition of Staphylococcus, strain H17C. Upon adding increasing increments of egg white to a medium containing a limited amount of biotion, growth was unaffected until a critical concentration of avidin was reached. At this level little or no growth of the microorganism occurred. At higher levels growth again occurred, the amount depending directly upon the level of egg white added. All Staphylococcus cultures tested (18 strains) were able to utilize biocytin in place of biotin. On a molar basis this substance appeared to have an activity equal to that of biotin. Strain S36 failed to grow in a biotin deficient medium to which 0.1 percent Tween 80 was added. All other strains tested were able to grow under these conditions. In comparison with other strains culture H10A appeared to require approximately 100 times as much biotin for growth. This high requirement could be demonstrated in spite of the fact that the culture was able to grow to a limited degree in the absence of added biotin. This culture also demonstrated similar high requirements for biocytin, homobiotion, and desthiobiotin in a biotin free medium.O artigo não apresenta resumo

Consequences of converting graded to action potentials upon neural information coding and energy efficiency

Information is encoded in neural circuits using both graded and action potentials, converting between them within single neurons and successive processing layers. This conversion is accompanied by information loss and a drop in energy efficiency. We investigate the biophysical causes of this loss of information and efficiency by comparing spiking neuron models, containing stochastic voltage-gated Na+ and K+ channels, with generator potential and graded potential models lacking voltage-gated Na+ channels. We identify three causes of information loss in the generator potential that are the by-product of action potential generation: (1) the voltage-gated Na+ channels necessary for action potential generation increase intrinsic noise and (2) introduce non-linearities, and (3) the finite duration of the action potential creates a ‘footprint’ in the generator potential that obscures incoming signals. These three processes reduce information rates by ~50% in generator potentials, to ~3 times that of spike trains. Both generator potentials and graded potentials consume almost an order of magnitude less energy per second than spike trains. Because of the lower information rates of generator potentials they are substantially less energy efficient than graded potentials. However, both are an order of magnitude more efficient than spike trains due to the higher energy costs and low information content of spikes, emphasizing that there is a two-fold cost of converting analogue to digital; information loss and cost inflation

Synthetic Mimic of Antimicrobial Peptide with Nonmembrane-Disrupting Antibacterial Properties

Proteolysis in dairy lactic acid bacteria has been studied in great detail by genetic, biochemical and ultrastructural methods. From these studies the picture emerges that the proteolytic systems of lactococci and lactobacilli are remarkably similar in their components and mode of action. The proteolytic system consists of an extracellularly located serine-proteinase, transport systems specific for di-tripeptides and oligopeptides (> 3 residues), and a multitude of intracellular peptidases. This review describes the properties and regulation of individual components as well as studies that have led to identification of their cellular localization. Targeted mutational techniques developed in recent years have made it possible to investigate the role of individual and combinations of enzymes in vivo. Based on these results as well as in vitro studies of the enzymes and transporters, a model for the proteolytic pathway is proposed. The main features are: (i) proteinases have a broad specificity and are capable of releasing a large number of different oligopeptides, of which a large fraction falls in the range of 4 to 8 amino acid residues; (ii) oligopeptide transport is the main route for nitrogen entry into the cell; (iii) all peptidases are located intracellularly and concerted action of peptidases is required for complete degradation of accumulated peptides.

Colliding Worlds: Asteroid research and the legitimization of war in space

Accepted versio

Pyrexia: aetiology in the ICU

Elevation in core body temperature is one of the most frequently detected abnormal signs in patients admitted to adult ICUs, and is associated with increased mortality in select populations of critically ill patients. The definition of an elevated body temperature varies considerably by population and thermometer, and is commonly defined by a temperature of 38.0 °C or greater. Terms such as hyperthermia, pyrexia, and fever are often used interchangeably. However, strictly speaking hyperthermia refers to the elevation in body temperature that occurs without an increase in the hypothalamic set point, such as in response to specific environmental (e.g., heat stroke), pharmacologic (e.g., neuroleptic malignant syndrome), or endocrine (e.g., thyrotoxicosis) stimuli. On the other hand, pyrexia and fever refer to the classical increase in body temperature that occurs in response to a vast list of infectious and noninfectious aetiologies in association with an increase in the hypothalamic set point. In this review, we examine the contemporary literature investigating the incidence and aetiology of pyrexia and hyperthermia among medical and surgical patients admitted to adult ICUs with or without an acute neurological condition. A temperature greater than 41.0 °C, although occasionally observed among patients with infectious or noninfectious pyrexia, is more commonly observed in patients with hyperthermia. Most episodes of pyrexia are due to infections, but incidence estimates of infectious and noninfectious aetiologies are limited by studies with small sample size and inconsistent reporting of noninfectious aetiologies. Pyrexia commonly triggers a full septic work-up, but on its own is a poor predictor of culture-positivity. In order to improve culturing practices, and better guide the diagnostic approach to critically ill patients with pyrexia, additional research is required to provide more robust estimates of the incidence of infectious and noninfectious aetiologies, and their relationship to other clinical features (e.g., leukocytosis). In the meantime, using existing literature, we propose an approach to identifying the aetiology of pyrexia in critically ill adults