Curli expression of enterotoxigenic Escherichia coli.

One hundred and four enterotoxin producing Escherichia coli strains of wide geographical origin were tested for the expression of curli fimbriae by transmission electronmicroscopy and by ELISA using curli-specific antibodies, as well as for the presence of curli-specific gene sequences by PCR. All isolates, irrespective of the production of the fimbriae, carried sequences specific for the structure (csgA) and for one of the regulator genes (crl) of curli expression, respectively. Curli fimbriae were detected in 56 strains (53.8 %). Thirty-six strains expressed curli only when growing at 30 degrees C, 4 isolates were weakly curliated at 37 degrees C only, while on 16 strains curli was observed at both temperatures. On isolates carrying curli at both temperatures the expression of the fimbria was significantly stronger at 30 degrees C than at 37 degrees C. Curli proficiency significantly, but not completely, correlated with the binding of the Congo Red dye. The expression of curli did not confer epithelial cell invasiveness to ETEC strains but, once expressed at 30 degrees C, it facilitated the adherence of the bacteria to plastic surfaces. Curli present in more than half of the ETEC strains and expressed preferentially at low temperatures could be a factor facilitating the environmental survival of this food- and water-borne pathogen.

Deflection of cosmic radiation near power lines--a theoretical approach.

The purpose of this work is to determine if, and to what extent, cosmic radiation can be deflected by power lines. As an alternative to experimental measurements, a computer program was developed to simulate particle trajectories. Starting from given initial values, the cosmic particles' trajectories through the electromagnetic field surrounding power lines are simulated. Particular efforts have been made to choose initial values that represent the actual physical condition of the cosmic radiation at ground level. The results show an average decrease in the particle flux density in an area below a power line and a corresponding increased flux between 12 m and 35 m on either side of the center of the power line. The average shift in flux density is, however, extremely small (less than 0.15% for low energy electrons alone, and less than 0.01% for total particle flux density) and probably not measurable with existing detector technology. The calculated particle deflection is far too small to be of any possible health significance.