Thermoregulation-dependent expression of Yersinia enterocolitica protein 1 imparts serum resistance to Escherichia coli K-12.

Resistance to the bactericidal action of normal human serum is one of the characteristics of virulent Yersinia enterocolitica. This property is attributable to the virulence plasmid harbored by pathogenic strains of the species. Serum resistance in Y. enterocolitica is thermoregulated, and its expression correlates well with the presence of virulence plasmid-encoded outer membrane proteins. To further examine the biochemical basis underlying resistance, we cloned a large segment (ca. 30 kilobases) of virulence plasmid DNA and studied the expression of plasmid-encoded outer membrane proteins in a serum-sensitive strain of Escherichia coli. The presence of the 160-kilodalton Y. enterocolitica-derived outer membrane protein 1 on E. coli transformants conferred a high degree of hydrophobicity, autoagglutinability, and resistance to serum killing. All of these properties were thermoregulated in E. coli with fidelity, suggesting that a functional thermoregulatory element was present in the cloned DNA. Elimination of protein 1 from the outer membrane of E. coli transformants by insertional inactivation of the structural gene with a Kanr gene cassette abrogated all of these properties and returned the serum-sensitive phenotype.     

Ca transport in membrane vesicles from pinto bean leaves and its alteration after ozone exposure

The influence of ozone on Ca²⁺ transport in plant membranes from pinto bean (Phaseolus vulgaris L. var Pinto) leaves was investigated in vitro by means of a filtration method using purified vesicles. Two transport mechanisms located at the plasma membrane are involved in a response to ozone: (a) passive Ca²⁺ influx into the cell and (b) active Ca²⁺ efflux driven by an ATP-dependent system, which has two components: a primary Ca²⁺ transport directly linked to ATP which is partially activated by calmodulin and a H⁺/Ca²⁺ antiport coupled to activity of a H⁺-ATPase. The passive Ca²⁺ permeability is increased by ozone. A triangular pulse of ozone stimulates a higher influx of Ca²⁺ than does a square wave, even though the total dose was the same (0.6 microliter per liter × hour). Leaves exposed to a square wave did not exhibit visible injury and were still able to recover from oxidant stress by activation of calmodulin-dependent Ca²⁺ extrusion mechanisms. On the other hand, leaves exposed to a triangular wave of ozone, exhibit visible injury and lost the ability of extruding Ca²⁺ out of the cell.     

Plasma catecholamines and their physiologic thresholds during the first ten days of life in sheep

We studied serial plasma catecholamine levels in healthy newborn sheep over the first ten days of life. The results show that plasma norepinephrine values in newborn sheep are 3-4 fold higher, and plasma epinephrine values are two-fold higher than values in term fetal sheep. These elevations are sustained over the first 10 days of life. Cardiovascular (heart rate and blood pressure) and metabolic parameters (glucose and free fatty acids) are also significantly elevated above fetal levels. We performed graded catecholamine infusions in newborn animals and adult ewes to determine the minimum plasma catecholamine concentrations necessary for discernible physiologic effects. In response to step-wise increases in epinephrine or norepinephrine infusion rates, there were immediate increases in blood pressure and other physiologic responses. This pattern was seen in both newborn and adult animals, and differed from previous observations in fetal sheep where log-linear, dose response curves characteristic of a threshold response were seen. These results suggest that during the first two weeks of life plasma catecholamine levels are elevated above the threshold value for physiologic responses. These sustained elevations in circulating catecholamines are important in the maintenance of physiologic homeostasis.     

Production of hydrogen peroxide by aryl-alcohol oxidase from the ligninolytic fungusPleurotus eryngii

Summary Production of extracellular hydrogen peroxide by fungal oxidases is been investigated as a requirement for lignin degradation. Aryl-alcohol oxidase activity is described in extracellular liquid and mycelium ofPleurotus eryngii and studied under non-limiting nitrogen conditions. This aryl-alcohol oxidase catalyses conversion of primary aromatic alcohols to the corresponding aldehydes and H₂O₂, showing no activity with aliphatic and secondary aromatic alcohols. The enzyme is stable at pH 4.0–9.0, has maximal activity at 45°–50°C and pH 6.0–6.5, is inhibited by Ag⁺, Pb²⁺ and NaN₃, and has aK _m of 1.2 mM using veratryl alcohol as substrate. A single protein band with aryl-alcohol oxidase activity was found in zymograms of extracellular and intracellular crude enzyme preparations fromP. eryngii.     

Genetic elements involved in Tn21 site-specific integration, a novel mechanism for the dissemination of antibiotic resistance genes.

Transposon Tn21 codes for a site-specific integration system, which is probably a novel recombination mechanism, responsible for the acquisition of resistance genes in this widespread family of transposons. Using insertion and deletion mutagenesis we have identified the genetic loci of the various recombination hot-spots (RHS) and of the gene product (the integrase) that catalyses the reaction. The site of recombination has been localized in two of the RHSs to the DNA sequence GTTAG, which is present at the 3' termini of a loosely conserved palindromic sequence of approximately 59 bp. This 59 bp sequence, which flanks the inserted genes in a number of naturally occurring transposons, is the only element required in cis for the recombination reaction.     

Rapid Increase of Pneumococcal Resistance to β-Lactam and Other Antibiotics in Isolates from the Respiratory Tract (Nagasaki,Japan: 1975–1994)

The susceptibility of 101 pneumococcal isolates from the respiratory tract during 1991–1994 was examined and compared with the susceptibility of isolates over the period of 1975–1990. A rapid increase of resistance was seen not only to penicillin but also other antimicrobial agents. During 1991–1994, 38% of all the isolates were resistant to penicillin. The rates of resistance during this period were 16–23% for three newer cephalosporins, 18% for imipenem, 69% for tetracycline, 31% for erythromycin, 20% for chloramphenicol and 9% for clindamycin. The use of antibiotics within one month prior to pneumococcal isolation was correlated with penicillin resistance (P < 0.05). Serotyping of the isolates by antiserum revealed differences in predominant types between penicillin-resistant (19F, 23F, 4) and -susceptible isolates (15, 4, 11A). Our data suggests that anti-pneumococcal antibiotics should be carefully chosen on the basis of susceptibility tests.     

Deoxynivalenol and contaminant mycoflora in freshly harvested Argentinian wheat in 1993

A mycological survey was carried out on wheat heads from the main production area of Argentina. The isolation frequency and relative density of species from genus Fusarium and dematiaceous fungi were calculated. F graminearum was the predominant Fusarium species; similar to that observed in the USA and Canada. An analysis of deoxynivalenol (DON) natural contamination also was performed on a limited number (44) of samples. DON contamination levels in positive samples ranged from 0.2 to 30 ppm. A stepwise regression procedure showed that, among the species analysed, F. graminearum relative density was related to the DON contamination level and that other prevalent fungi did not influence or modify that relationship.     

Quasiperiodicity route to chaos in a biochemical system.

The numerical study of a glycolytic model formed by a system of three delay differential equations reveals a quasiperiodicity route to chaos. When the delay changes in our biochemical system, we can observe the emergence of a strange attractor that replaces a previous torus. This behavior happens both under a constant input flux and when the frequency of the periodic substrate input flux changes. The results obtained under periodic input flux are in agreement with experimental observations.