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To examine the genetic background of avian pathogenic Escherichia coli (APEC) that affects virulence of this microorganism, we characterized the virulence genes of 101 APEC strains isolated from infected chickens between 1985~2005. Serotypes were determined with available anti-sera and median lethal doses were determined in subcutaneously inoculated chicks. The virulence genes we tested included ones encoding type 1 fimbriae ( fimC ), iron uptake-related ( iroN , irp2 , iucD , and fyuA ), toxins ( lt , st , stx1 , stx2 , and vat ), and other factors ( tsh , hlyF , ompT , and iss ). Twenty-eight strains were found to be O1 (2.0%), O18 (3.0%), O20 (1.0%), O78 (19.8%), and O115 (2.0%) serotypes. The iroN (100%) gene was observed most frequently followed by ompT (94.1%), fimC (90.1%), hlyF (87.1%), iss (78.2%), iucD (73.3%), tsh (61.4%), fyuA (44.6%), and irp2 (43.6%). The strains were negative for all toxin genes except for vat (10.9%). All the strains were classified into 27 molecular pathotypes (MPs). The MP25, MP19, and MP10 pathotypes possessing iroN-fimC-ompT-hlyF-iucD-tsh-iss-irp2-fyuA (22.8%), iroN-fimC-ompT-hlyF-iucD-tsh-iss (21.8%), and iroN-fimC-ompT-hlyF-iss (11.9%) genotypes, respectively, were predominant. Redundancy of iron uptake-related genes was clearly observed and some strains were associated with higher mortality than others. Therefore, strains with the predominant genotypes can be used for diagnosis and vaccine.

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This paper presents the electrical contact behaviors of gold-to-gold thin-film contacts under high current conditions and describes the major factors that influence these contact behaviors for radio frequency microelectromechanical system switches. The fundamental phenomena in the contact resistance versus contact force curve were investigated with a contact measurement setup, which we devised. Based on the experimental results, the contact resistance behavior with increasing contact force can be divided into three regions: first, an unstable contact regime before the minimum contact force is reached; second, a stable contact regime where the plastic deformation of the asperities explains the behavior and, finally, a saturated regime where the thickness effect of the film on a hard substrate becomes evident. The minimum contact force required for a stable contact depended on the roughness of the surface and the current flow through the contact. The smooth surface of the Au film and the metal softening caused by a high current flow of 100 mA had the effect of lowering the minimum contact force. After the minimum contact force is exceeded, the contact resistance initially follows the asperity plastic deformation behavior, where the contact resistance is related to the resistivity and hardness of the contact material. In the higher contact force regime, the decrease in the contact resistance becomes almost negligible. With increasing contact force, the effective contact area is limited by the effect of the film thickness on a hard substrate. From these results, we found the principal factors influencing the contact behaviors of the Au-to-Au contacts to be the resistivity, hardness and softening temperature of the contact materials and the design factors such as the surface roughness, the film thickness and the substrate.