ABSTRACT
The Newtonian gravitational constant G was determined by means of a novel beam-balance experiment with an accuracy comparable to that of the most precise torsion-balance experiments. The gravitational force of two stainless steel tanks filled with 13 521 kg mercury on 1.1 kg test masses was measured using a commercial mass comparator. A careful analysis of the data and the experimental error yields G=6.674 07(22)x10(-11) m(3) kg(-1) s(-2). This value is in excellent agreement with most values previously obtained with different methods.
ABSTRACT
Water samples from the Monocacy River in Frederick County, Maryland, yielded twenty-four isolates which were resistant to tetracycline (TeR, 25 micrograms/ml). Although these organisms were not initially cultured on a coliform-selective medium, twenty-two of the isolates were Gram-negative and carriers of antibiotic resistance to five or more antibiotics; erythromycin, methicillin, novobiocin, penicillin and tetracycline. Of the isolates 45% were biochemically identified as Providencia stuartii; one isolate which contained a 29.4 kilobase plasmid carried the determinant for tetracycline resistance.
Subject(s)
Enterobacteriaceae/isolation & purification , Tetracycline Resistance , Water Microbiology , Ampicillin Resistance , Chloramphenicol Resistance , Culture Media , DNA, Bacterial/genetics , Drug Resistance, Microbial , Electrophoresis, Agar Gel , Enterobacteriaceae/drug effects , Enterobacteriaceae/genetics , Erythromycin/pharmacology , Fresh Water , Methicillin/pharmacology , Novobiocin/pharmacology , Penicillin Resistance , R Factors , Streptomycin/pharmacology , Transformation, BacterialABSTRACT
Three classes of phosphotransferase system mutants in Salmonella typhimurium were selected through their resistance to 3-deoxy-3-fluoro-D-glucose (DFG). Strains with mutations in the ptsH (HPr) and/or pts I (enzyme I) genes were selected on medium containing lactate plus DFG. Strains with mutations in ptsH but not pstI were selected on medium containing fructose plus DFG. Clones isolated from fructose plus DFG semisolid plates and selected for ability to swarm were mutant in either ptsH or ptsG. Mutants of the latter class were defective in enzyme IIB', a membrane component of the glucose transport system. Some pleiotropic properties of one representative ptsG mutant are described.
