A genetic and biochemical study of streptomycin- and spectinomycin-resistance in Salmonella typhimurium

Summary In Salmonella typhimurium, streptomycin resistance can occur by mutation at the strA or the strB mutants have altered ribosomes which are refractory to the drug in cell-free amino acid incorporation systems, and in ³H-dihydrostreptomycin binding studies. StrB mutants, unlike the strA mutants, are resistant to several aminoglycoside antibiotics and resistance is not due to a mutational change in the cell's protein synthetic machinery. Spectinomycin resistant mutants of S. typhimurium also fall into two classes, only one of which is ribosomal in mechanism. The spcA and spcB loci are closely linked to strA, aroC, and argG on the S. typhimurium linkage map.     

Urinary Concentrating Ability in Women with Asymptomatic Bacteriuria in Pregnancy

The incidence of impaired renal concentrating ability in pregnant women with asymptomatic significant bacteriuria is significantly less than previously reported when osmolality readings are performed on every urine specimen obtained during the 24 hours'' deprivation of fluids. The concentrating defect is more considerable as pregnancy progresses. The lower the maximum urinary osmolality the more difficult is the treatment of the patient, and the higher the incidence of acute pyelonephritis.     

Fascioliasis—A Large Outbreak

Forty-four cases of liver fluke infestation (fascioliasis hepatica) were diagnosed near Chepstow, Monmouthshire, in 1968. Intramuscular emetine hydrochloride and oral chloroquine given to the adults and children, respectively, were well tolerated. Assessment by repeated stool examination, complement fixation and liver function tests, and full blood counts indicated that treatment had been effective in most cases. It is recommended that both the growth and the sale of watercress should be strictly controlled.     

Submerged reefs and terraces on the shelf edge of the Great Barrier Reef,Australia

The morphology and distribution of seabed features on the shelf edge and upper slope adjacent to the Great Barrier Reef, Australia, has been examined using shallow seismic profiling, side-scan sonar and precision echo sounding data, supplemented by submersible investigations. The data reveal a submerged barrier reef system at different locations between 15° 45 S and 21° 00 S. At two locations, an extensive offshore platform rising above the 50 m isobath and extending for over 20 km parallel to the shelf edge is backed by a relict lagoon at an average depth of 75 m. In addition, outer shelf and upper slope terraces are found at many depths; however, only some occur consistently throughout the region while most others occur only locally. Frequency distributions indicate the greatest occurrence of features at depths of 44–46, 60–66, 72–78, 80–84, 102–106 and 146–148 m. Caution should be exercised when interpreting these features with respect to specific lower sea level stands.     

Assessment of uncoupling by amiloride analogs.

The amiloride analogs N5-methyl-N5-isobutylamiloride, N5-ethyl-N5-isopropylamiloride, and N5,N5-hexamethyleneamiloride are frequently used to investigate NaH exchange on the premise that they are highly specific inhibitors of the NaH-antiporters. We assessed the relative protonophoric activity of these compounds in reconstituted and native membrane vesicles, using acridine orange fluorescence to measure intravesicular pH. All the compounds tested were found to be potent protonophores at concentrations which are normally used to demonstrate inhibition of NaH exchange. Uncoupling was dependent on both the pH of the assay system and the total amount of lipid present. At the pH optima, which lay in a range from 7.5 to 8.5, these amiloride analogs were more potent uncouplers than the classical protonophore carbonyl cyanide m-chlorophenylhydrazone. Therefore, extreme care must be taken in the interpretation of results obtained using these or similar derivatives of amiloride.     

Quenching of Hoechst 33258 fluorescence in erythroid precursors.

Quenching of the fluorescence of DNA-bound Hoechst 33258 in erythroid precursors was studied by flow cytometry and cytochemistry. This quenching artifact may affect the measurement of ploidy in specific cases. The bone marrow cells of two patients with hemolytic disease and active erythropoiesis contained subpopulations of cells with an apparent hypodiploid DNA content as measured by flow cytometry of paraformaldehyde-fixed cells stained with Hoechst 33258. No aneuploidy was detected in either of the two cases when cells were stained with mithramycin or 7-aminoactinomycin D. Cells exhibiting reduced Hoechst 33258 fluorescence expressed glycophorin A and low amounts of CD36, and were therefore erythroid precursors. In one case studied, the number of cells with reduced Hoechst 33258 fluorescence and glycophorin A expressed agreed well with the number of cells containing nuclear hemoglobin. In the other case, hemoglobin was present in a significant proportion of nucleated cells. Calculated values for the efficiency of resonance energy transfer from Hoechst 33258 to hemoglobin were in accordance with the observed levels of quenching (approximately 10%). However, the results could also be explained by hemoglobin reabsorption of Hoechst 33258 fluorescence. Nuclei stained with Hoechst 33258 showed uniform fluorescence, probably due to extraction of hemoglobin during the isolation procedure.