The objective of this study was to ascertain the nationwide prevalence and antimicrobial resistance rates of Salmonella spp. and Escherichia coli amongst domesticated finisher pigs. Fecal samples (n=840) were collected at 84 slaughterhouses in Korea in May 2009. Salmonella spp. was isolated from 21 of the 840 samples (2.5%), and comprised the following isolated serotypes: Salmonella rissen, Salmonella derby, Salmonella typhimurium. Antimicrobial susceptibility testing was performed for eight antimicrobials. Salmonella resistance was tetracycline (76.19%); nitrofurantoin (38.10%); kanamycin (33.33%); chloramphenicol, sulfamethoxazole/trimethoprim and cephalothin (28.57%); polymyxin B (9.52%); and ampicillin/sulbactam (4.76%), and E. coli resistance was tetracycline (87.11%); chloramphenicol (66.24%); kanamycin (51.68%); sulfamethoxazole/trimethoprim (51.29%); cephalothin (8.38%); nitrofurantoin (5.15%); ampicillin/sulbactam (4.64%); and polymyxin B (0.52%). Tetracycline resistance was most common. Surprisingly, 28.57 and 66.24% of the Salmonella spp. and E. coli isolates, respectively, were resistant to chloramphenicol, which has been banned from agricultural use in Korea for some time. A wide range of strains displayed multi-antimicrobial resistance: 14 out of 21 (66.66%) and 611 out of 776 (78.72%) of the Salmonella and E. coli isolates, respectively. Salmonella spp. and E. coli demonstrate an appreciable broad-spectrum, (multi)-antimicrobial resistance, which is a potential public health concern. A continuous antibiotic surveillance program may be worthwhile.
Pseudomonas sp. HK-6 is able to utilize hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) as a sole nitrogen source. The HK-6 strain was stimulated to produce an exopolymer, mainly alginate, as a stress response when grown in LB broth containing RDX, synthesizing ~230 μg/mL after 48 h. The algA mRNA levels in HK-6 increased by 7-8-fold after 2-6 h of exposure to 0.1 mM RDX, as measured by RT-qPCR. HK-6 was able to degrade ~25 % of 0.1 mM RDX after 20 days and 60 % after 50 days, whereas the pnrB null mutant only degraded less than 1 % after 50 days. The introduction of an algD promoter-pnrB gene fusion into the pnrB mutant fully restored RDX-degradation capability. To facilitate a study of PnrB action on RDX, a His6-PnrB fusion protein was heterologously expressed in E. coli BL21 cells, and the enzymatic activity on RDX was assayed by measuring the decrease in absorbance at 340 nm due to NADH oxidation. At the fixed condition of 0.1 mM RDX, 0.2 mM NADH, and 1 μg His6-PnrB, the absorbance at 340 nM gradually decreased and reached to its minimum value after 30 min. However, calculating the V max and K m values of PnrB for RDX was challenging due to extremely low solubility of RDX in water. The results clearly indicate the potential use of the algD promoter in studies of some genes in Pseudomonas species.
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