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Long Depletion Time of Enrofloxacin in Rainbow Trout (Oncorhynchus mykiss). Dario Lucchetti, 2004.The international production of farmed fish has been growing continuously over recent years . Until now few veterinary drugs have been approved by the European Union for use in aquaculture, and this has favored the off-label use of products authorized for use in food-producing animal species different from fishes among fish farmers . Adequate field studies are lacking, especially for those species called minor species which are consumed extensively only in some European countries . In the present investigation we studied the depletion of the fluoroquinolone antibacterial enrofloxacin over time in a minor species, the rainbow trout (Oncorhynchus mykiss), reared on a real fish farm and treated with medicated feed (10 mg kg of trout body weight–1 day–1) . Edible tissue samples (muscle plus skin in natural proportions) and fish bone samples were analyzed for enrofloxacin and for its major metabolite, ciprofloxacin, by high-performance liquid chromatography with fluorescence detection at different times after the end of treatment . Our results show that at 500°C-day (in which degree-days are calculated by multiplying the mean daily water temperature by the total number of days on which the temperature was measured), which is the minimum withdrawal period established by European Economic Commission Directive No . 82/2001 for any type of product administered off-label, edible trout tissues might still contain about 170 µg of enrofloxacin kg–1, whereas the maximum residue level for enrofloxacin plus ciprofloxacin is set at 100 µg kg–1 . To our knowledge, no studies of the depletion of enrofloxacin in rainbow trout have been performed . On the basis of the data obtained in the present study, we suggest a more appropriate withdrawal time of 816°C-day for the sum of enrofloxacin plus ciprofloxacin levels in rainbow trout muscle plus skin tissues . Phage  Red-Mediated Adaptive Mutation.Anthony R. Poteete, 2002.Replacement of the recBCD genes of Escherichia coli with the red recombination genes of bacteriophage lambda results in a strain in which adaptive mutation occurs at an elevated frequency . Like RecBCD-dependent adaptive mutation, Red-mediated adaptive mutation is dependent upon recA and ruvABC functions . FolM, A New Chromosomally Encoded Dihydrofolate Reductase in Escherichia coli. Moshe Giladi, 2003.Escherichia coli (thyA  folA) mutants are viable and can grow in minimal medium when supplemented with thymidine alone . Here we present evidence from in vivo and in vitro studies that the ydgB gene determines an alternative dihydrofolate reductase that is related to the trypanosomatid pteridine reductases . We propose to rename this gene folM .
Differential Growth Response of Colony-Forming  - and
 -Proteobacteria in Dilution Culture and Nutrient Addition Experiments from Lake Kinneret (Israel), the Eastern Mediterranean Sea, and the Gulf of Eilat.Jarone Pinhassi, 2003.Even though it is widely accepted that bacterioplankton growth in lakes and marine ecosystems is determined by the trophic status of the systems, knowledge of the relationship between nutrient concentrations and growth of particular bacterial species is almost nonexistent . To address this question, we performed a series of culture experiments with water from Lake Kinneret (Israel), the eastern Mediterranean Sea, and the Gulf of Eilat (northern Red Sea) . In the initial water samples, the proportion of CFU was typically <0.002% of the 4',6'-diamidino-2-phenylindole (DAPI) counts . During incubation until the early stationary phase, the proportion of CFU increased to 20% of the DAPI counts and to 2 to 15% of the DAPI counts in unenriched lake water and seawater dilution cultures, respectively . Sequencing of the 16S ribosomal DNA of colony-forming bacteria in these cultures consistently revealed an abundance of -proteobacteria, but notable phylogenetic differences were found at the genus level . Marine dilution cultures were dominated by bacteria in the Roseobacter clade, while lake dilution cultures were dominated by bacteria affiliated with the genera Sphingomonas and Caulobacter . In nutrient (glucose, ammonium, phosphate) addition experiments the CFU comprised 20 to 83% of the newly grown cells . In these incubation experiments fast-growing
-proteobacteria dominated; in the marine experiments primarily different Vibrio and Alteromonas species appeared, while in the lake water experiments species of the genera Shewanella, Aeromonas, and Rheinheimera grew . These results suggest that major, but different,
-proteobacterial genera in both freshwater and marine environments have a preference for elevated concentrations of nutrients and easily assimilated organic carbon sources but are selectively outcompeted by
-proteobacteria in the presence of low nutrient concentrations .
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