Search

Abstract The intention of this study was to identify the bacterial pathogens infecting Oreochromis niloticus (Nile tilapia) and Clarias gariepinus (African catfish), and to establish the antibiotic susceptibility of fish bacteria in Uganda. A total of 288 fish samples from 40 fish farms (ponds, cages, and tanks) and 8 wild water sites were aseptically collected and bacteria isolated from the head kidney, liver, brain and spleen. The isolates were identified by their morphological characteristics, conventional biochemical tests and Analytical Profile Index test kits. Antibiotic susceptibility of selected bacteria was determined by the Kirby-Bauer disc diffusion method. The following well-known fish pathogens were identified at a farm prevalence of; Aeromonas hydrophila (43.8%), Aeromonas sobria (20.8%), Edwardsiella tarda (8.3%), Flavobacterium spp. (4.2%) and Streptococcus spp. (6.3%). Other bacteria with varying significance as fish pathogens were also identified including Plesiomonas shigelloides (25.0%), Chryseobacterium indoligenes (12.5%), Pseudomonas fluorescens (10.4%), Pseudomonas aeruginosa (4.2%), Pseudomonas stutzeri (2.1%), Vibrio cholerae (10.4%), Proteus spp. (6.3%), Citrobacter spp. (4.2%), Klebsiella spp. (4.2%) Serratia marcescens (4.2%), Burkholderia cepacia (2.1%), Comamonas testosteroni (8.3%) and Ralstonia picketti (2.1%). Aeromonas spp., Edwardsiella tarda and Streptococcus spp. were commonly isolated from diseased fish. Aeromonas spp. (n = 82) and Plesiomonas shigelloides (n = 73) were evaluated for antibiotic susceptibility. All isolates tested were susceptible to at-least ten (10) of the fourteen antibiotics evaluated. High levels of resistance were however expressed by all isolates to penicillin, oxacillin and ampicillin. This observed resistance is most probably intrinsic to those bacteria, suggesting minimal levels of acquired antibiotic resistance in fish bacteria from the study area. To our knowledge, this is the first study to establish the occurrence of several bacteria species infecting fish; and to determine antibiotic susceptibility of fish bacteria in Uganda. The current study provides baseline information for future reference and fish disease management in the country.

Abstract The local atomistic structure in bulk SixGe1−x alloys in the whole composition range 0 < x < 1 was investigated experimentally and theoretically. By extended X-ray absorption fine structure measurements in Czochralski-grown bulk SiGe crystals it is found that bulk SiGe is a random mixture and that the Ge–Ge, Ge–Si and Si–Si bond lengths maintain distinctly different lengths and vary in a linear fashion as a function of alloy composition across the entire composition range 0 < x < 1, in good agreement with expectations derived from the ab-inito electronic structure calculations. The results indicate that SiGe is a typical disorder material and that the bond lengths and bond angles are distorted with alloy composition in SiGe. [ABSTRACT FROM AUTHOR]

Capabilities of the reverse Monte Carlo method for characterizing the short-range structural correlations of solids were examined in the analysis of extended energy-loss fine structure (EXELFS). Since this method gives a three-dimensional atomic configuration consistent with the experimental EXELFS spectra, one can extract the statistical distributions of bond lengths, coordination numbers and bond angles of atom species of interest, which have been hard to achieve by conventional EXELFS analysis. The method was applied for the determination of amorphous Si structures and the damaged structure of an electron-irradiated SiC crystal. Advantages and disadvantages of the present method over the precise diffraction intensity measurement are discussed. [ABSTRACT FROM AUTHOR]

The dehydriding reaction of single-phase a- AlH3 was investigated by in situ microscopic observations combined with thermal and surface analyses. Before the dehydriding reaction, primary AlH3 particles of size 100 nm-1 um were thought to be covered by an oxide layer with a thickness of less than 5 nm. Both the precipitation/grain-growth of metallic Al of size 1-50 nm and an increase in 'boundary space' were clearly observed inside the particles, while the morphologies of the particles covered by the layer did not change during the dehydriding reaction. This preliminary report provides fundamental information for a further study of AlH3 as a possible hydrogen storage material. [ABSTRACT FROM AUTHOR]