In this study, the molecular structures of tet(M) and tet(G) carried by tetracycline (Tc) resistant bacteria in intestinal microflora from the imported ornamental fish were characterized and compared with each other depend on the imported countries. Of the total isolates, approximately 8.9% of the Ent-lac+ (lactose fermentative bacteria on coliform media) Tc resistant isolates in fish from three different countries , Singapore, Taiwan and Brazil, were appeared to contain tet(M). Three representative isolates of different countries, Aeromonas spp. JSM-1 (Singapore), JTM-1 (Taiwan) and JBM-1 (Brazil), were isolated and analyzed the molecular structures of tet(M) gene. Interestingly, partial sequence of tet(M) genes (1099 bp) in JBM-1 (Brazil) showed 99.5% homology with the tet(M) found in the Vibrio spp. RV16 isolate, obtained from marine fish in Korea and known to carry Tn1545 parent type of tet(M). In contrast, tet(M) gene in JSM-1 and JTM-1 showed mosaic structure of Tn1545 and Tn916, and 100% homology with each other. It may suggest the presence of various characteristics in terms of tet(M) gene structure. The determined sequence of the tet(G) from Aeromonas spp. JSG-1 and JBG-1 isolated from Singapore and Indonesia ornamental fish respectively showed similar nucleotide sequence homology but revealed a few nucleotide changes in comparison with the sequence of the prototype tet(G) gene (S52437 in GenBank).
For comparison of tetracycline-resistant (Tc R) genes, we obtained 21 and 14 Tc R Staphylococcus spp. from marine environment and human patient, respectively. Although all isolates from human were identified as Staphylococcus aureus, higher proportion of Tc R isolates (12 out of 14) from human were utilizing tet(M) gene compared to that of Tc R isolates (6 out of 21) from marine environment. Additionally, collaborated utilization of tet(M) and erm(A) in Tc R-Em R S. aureus in human patient, but not in Tc R Staphylococcus spp. isolates from marine environment was also characterized. Based on the nucleotide sequence of transposon related to Tc R gene, we confirmed the origin of tet(M) gene in Tc R Staphylococci isolated from marine environments and human are derived from Tn916/1545-like and Tn5801 transposon, respectively. It is the first report showing the presence of Tn5801 in all Tc R S. aureus carrying tet(M) in human patient. Alignment of the fully sequenced tet(M) from marine environmental isolates was also agreed with the determined transposons by showing the genomic mosaic structure composed with three genomic parts from Tn916/1545 and unknown transposons. Genetic characteristics of these tet(M) in environmental isolates were similar to each other but different from those in isolates from human showing only tet(M) from Tn916/5801 type. It may imply the presence of less dramatic communication of antibiotic resistant genes between Staphylococci isolated from marine environment and human.
The crystallization of amorphous silicon (a-Si) was achieved by field-aided lateral crystallization (FALC). Under the influence of an electric field, Cu is found to drastically enhance the lateral crystallization velocity of a-Si. When an electric field of 30 V/cm was applied to selectively Cu-deposited a-Si films during heat treatment at 350°C, dendrite-shaped crystallization of a-Si progressed toward the Cu-free region, and the crystallization from the negative electrode side toward the positive electrode side was accelerated. The Cu-FALC polycrystalline-silicon (poly-Si) film has a crystalline volume fraction of 58% with 300-nm-long, rod-shaped grains. Low-temperature crystallization of a-Si in an electric field appears to be caused by enhanced migration of the Cu ions in the a-Si region.
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