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At least 1,063 records · Page 59Linked to original sources
PubMed1973

Enumeration of tubercle bacilli in sputum of patients with pulmonary tuberculosis.

A method for precise microscopic enumeration of acid-fast bacilli in the sputum of patients with pulmonary tuberculosis is described. The total number of acid-fast bacilli and the number of culturable cell units of tubercle bacilli per milliliter of sputum were determined in 269 specimens from 28 patients collected prior to and/or during chemotherapy, to establish the usefulness of the procedure for evaluation of the effects of chemotherapy. Prior to or very early in the course of therapy, there was good agreement between microscopically and culturally measurable bacilli in 27 of 28 patients. Thereafter, there were systematic divergences in five patients and occasional divergences in most others. Yet, in general, in 20 of the 28 patients, the microscopically determined population provided a useful measure of the number of culturable tubercle bacilli present. Although the microscopic procedure does not allow species identification of mycobacteria or differentiation between viable and nonviable cells, it often provided, within hours rather than days or weeks, useful information on the residual burden of acid-fast bacilli in sputum during chemotherapy. The nature of the disease in those patients in whom microscopy failed to provide useful information is discussed.

Adolescent↗
PubMed2005

Analysis of the contribution of individual substituents in 4,6-aminoglycoside-ribosome interaction.

The 4,6-disubstituted 2-deoxystreptamines interfere with protein biosynthesis by specifically targeting the ribosomal A site. These drugs show subtle variations in the chemical groups of rings I, II, and III. In the present study we used site-directed mutagenesis to generate mutant strains of Mycobacterium smegmatis mc(2)155 SMR5 DeltarrnB with mutations in its single rRNA allele, rrnA. This genetic procedure gives rise to strains carrying homogeneous populations of mutant ribosomes and was used to study the contribution of individual chemical substituents to the binding of 4,6-disubstituted aminoglycosides. X-ray crystal structures of geneticin and tobramycin complexed to oligonucleotides containing the minimal bacterial ribosomal A site were used for interpretation of MICs determined for a panel of 4,6-aminoglycosides, including tobramycin, kanamycin A, kanamycin B, amikacin, gentamicin, and geneticin. Surprisingly, the considerable differences present within ring III did not seem to alter the interaction of the drug with the ribosome, as determined by site-directed mutagenesis of the A site. In contrast, subtle variations in ring I significantly influenced binding: (i) a 4'-hydroxyl moiety participates in the proper drug target interaction; and (ii) a 2'-amino group contributes an additional positive charge to ring I, making the drug less susceptible to any kind of sequence alteration within the decoding site, most notably, to conformational changes induced by transversion of U1495 to 1495A. The 4-amino-2-hydroxyl-1-oxobutyl extension at position 1 of ring II of amikacin provides an additional anchor and renders amikacin less dependent on the structural conformation of nucleotide U1406 compared to the dependencies of other kanamycins. Overall, the set of interactions forming the complex between drug substituents and nucleotides of the A site constitutes a network in which the interactions can partly compensate for each other when they are disrupted.

Aminoglycosides↗
PubMed2006

Binding of neomycin-class aminoglycoside antibiotics to mutant ribosomes with alterations in the A site of 16S rRNA.

Aminoglycoside antibiotics that bind to the aminoacyl-tRNA site (A site) of the ribosome are composed of a common neamine core in which a glycopyranosyl ring is attached to position 4 of a 2-deoxystreptamine moiety. The core is further substituted by one (ribostamycin), two (neomycin and paromomycin), or three (lividomycin A) additional sugars attached to position 5 of the 2-deoxystreptamine. To study the role of rings III, IV, and V in aminoglycoside binding, we used isogenic Mycobacterium smegmatis DeltarrnB mutants carrying homogeneous populations of mutant ribosomes with alterations in the 16S rRNA A site. MICs were determined to investigate drug-ribosome interactions, and the results were compared with that of the previously published crystal structure of paromomycin bound to the ribosomal A site. Our analysis demonstrates that the stacking interaction between ring I and G1491 is largely sequence independent, that rings III and IV each increase the strength of drug binding to the ribosome, that ring IV of the 6'-NH3+ aminoglycosides compensates for loss of interactions between ring II and U1495 and between ring III and G1491, that the aminoglycosides rely on pseudo-base pairing between ring I and A1408 for binding independently of the number of sugar rings attached to the neamine core, that addition of ring V to the 6'-OH 4,5-aminoglycoside paromomycin does not alter the mode of binding, and that alteration of the U1406.U1495 wobble base pair to the Watson-Crick interaction pair 1406C-1495G yields ribosomal drug susceptibilities to 4,5-aminoglycosides comparable to those seen with the wild-type A site.

Anti-Bacterial Agents↗
PubMed1977

Use of nuclepore filters for counting bacteria by fluorescence microscopy.

Polycarbonate Nuclepore filters are better than cellulose filters for the direct counting of bacteria because they have uniform pore size and a flat surface that retains all of the bacteria on top of the filter. Although cellulose filters also retain all of the bacteria, many are trapped inside the filter where they cannot be counted. Before use, the Nuclepore filters must be dyed with irgalan black to eliminate autofluorescence. Direct counts of bacteria in lake and ocean waters are twice as high with Nuclepore filters as with cellulose filters.

Bacteria↗
PubMed2003

Bacterioplankton community shifts in an arctic lake correlate with seasonal changes in organic matter source.

Seasonal shifts in bacterioplankton community composition in Toolik Lake, a tundra lake on the North Slope of Alaska, were related to shifts in the source (terrestrial versus phytoplankton) and lability of dissolved organic matter (DOM). A shift in community composition, measured by denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes, occurred at 4 degrees C in near-surface waters beneath seasonal ice and snow cover in spring. This shift was associated with an annual peak in bacterial productivity ([(14)C]leucine incorporation) driven by the large influx of labile terrestrial DOM associated with snow meltwater. A second shift occurred after the flux of terrestrial DOM had ended in early summer as ice left the lake and as the phytoplankton community developed. Bacterioplankton communities were composed of persistent populations present throughout the year and transient populations that appeared and disappeared. Most of the transient populations could be divided into those that were advected into the lake with terrestrial DOM in spring and those that grew up from low concentrations during the development of the phytoplankton community in early summer. Sequencing of DNA in DGGE bands demonstrated that most bands represented single ribotypes and that matching bands from different samples represented identical ribotypes. Bacteria were identified as members of globally distributed freshwater phylogenetic clusters within the alpha- and beta-Proteobacteria, the Cytophaga-Flavobacteria-Bacteroides group, and the ACTINOBACTERIA:

Animals↗
PubMed2004

Microbial biogeography along an estuarine salinity gradient: combined influences of bacterial growth and residence time.

Shifts in bacterioplankton community composition along the salinity gradient of the Parker River estuary and Plum Island Sound, in northeastern Massachusetts, were related to residence time and bacterial community doubling time in spring, summer, and fall seasons. Bacterial community composition was characterized with denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S ribosomal DNA. Average community doubling time was calculated from bacterial production ([(14)C]leucine incorporation) and bacterial abundance (direct counts). Freshwater and marine populations advected into the estuary represented a large fraction of the bacterioplankton community in all seasons. However, a unique estuarine community formed at intermediate salinities in summer and fall, when average doubling time was much shorter than water residence time, but not in spring, when doubling time was similar to residence time. Sequencing of DNA in DGGE bands demonstrated that most bands represented single phylotypes and that matching bands from different samples represented identical phylotypes. Most river and coastal ocean bacterioplankton were members of common freshwater and marine phylogenetic clusters within the phyla Proteobacteria, Bacteroidetes, and ACTINOBACTERIA: Estuarine bacterioplankton also belonged to these phyla but were related to clones and isolates from several different environments, including marine water columns, freshwater sediments, and soil.

Bacteria↗
PubMed1970

Measurement of CO(2) Assimilation in Soils: an Experiment for the Biological Exploration of Mars.

A method is described for the measurement of CO(2) assimilation by microorganisms in soils. A determination involves exposing soil to CO(2), pyrolyzing the exposed soil, trapping the organic pyrolysis products on a column of firebrick coated with CuO, combusting the trapped organics by heating, and measuring the radioactivity in the CO(2) produced in the combustion. The detection of significant levels of C in the trapped organic fraction appears to be an unambiguous indication of biological activity. The CO(2) which is adsorbed or exchanged into soils by nonbiological processes does not interfere. The method easily detects the CO(2) fixed by 10 to 10 algae after light exposure for 3 to 24 hr. Assimilation of C is also demonstrable in dark-exposed soils containing 10 to 10 heterotrophic bacteria. Possible applications of the method in the biological exploration of Mars are discussed.

Journal Article↗
PubMed1992

A 34- to 38-kilodalton Cryptococcus neoformans glycoprotein produced as an exoantigen bearing a glycosylated species-specific epitope.

Three monoclonal antibodies (MAbs), all of the immunoglobulin G1 subclass, were raised against Cryptococcus neoformans by using the technique of cyclophosphamide ablation of B-cell responses against shared epitopes of the cross-reactive fungus Trichosporon beigelii. MAb 3C2 was reactive against the encapsulated and nonencapsulated isolates of C. neoformans var. neoformans by enzyme-linked immunosorbent assay (ELISA) and Western blot (immunoblot), and in addition to a 34- to 38-kDa determinant, it recognized a series of lower-molecular-weight species. 3C2 also reacted strongly with culture supernatant preparations of C. neoformans var. neoformans by ELISA. 3C2 showed no recognition of either T. beigelii or C. neoformans var. gattii antigens. Enzymatic deglycosylation followed by reaction with 3C2 on Western blots revealed that sialic acid was an integral part of the determinant, together with N-acetylglucosaminyl-asparagine and alpha-mannose. Proteolytic digestion showed that the epitope was pepsin sensitive and that it also contained tryptophan and glycine and/or leucine as determinants of recognition by 3C2. The pI of the glycoprotein was 7.1. Affinity chromatography-purified antigen did not exhibit proteolytic activity on sodium dodecyl sulfate-polyacrylamide substrate gels. Indirect fluorescence antibody tests revealed that 3C2 labelling was confined to the cell membrane and cytoplasm of yeasts. The remaining MAbs, 7H4 and 5G5, recognized both capsulated and nonencapsulated strains of C. neoformans var. neoformans by both ELISA and Western Blot, identifying linear determinants with molecular masses of 36 and 30 kDa. They were unreactive against culture supernatant antigen (exoantigen) from either variant of C. neoformans.

Animals↗
PubMed1992

In vitro activation of the Serratia marcescens hemolysin through modification and complementation.

The hemolytic activity of Serratia marcescens is determined by two polypeptides, termed ShlA and ShlB. ShlA is synthesized as an inactive precursor (ShlA*) and secreted with the help of ShlB, which is located in the outer membrane. In this study, it is shown that a cell lysate containing ShlB as well as partially purified ShlB converted ShlA* to the active ShlA hemolysin. ShlA remained active after removal of ShlB by column chromatography. In contrast to the stable modification of ShlA* by ShlB, a reversible activation was achieved by adding to ShlA* an N-terminal fragment of ShlA (ShlA16), consisting of 269 amino acid residues of ShlA and 18 residues of the vector. The nonhemolytic ShlA16 complemented ShlA* only when it was synthesized in an ShlB-producing cell. A deletion derivative of ShlA*, lacking residues 4 to 117, was complemented by ShlA16 but not activated by ShlB. Activation of ShlA* by ShlB at 4 degrees C proceeded at a much slower rate than complementation by ShlA16. It is concluded that ShlA* is modified by ShlB. ShlA16 modified by ShlB complements the missing modification of ShlA* in trans. Modification by ShlB occurs in the N-terminal part of ShlA*, which is also the reaction in vivo which results in active ShlA hemolysin in the culture supernatant. The HpmA hemolysin of Proteus mirabilis, which is very similar to ShlA, was also activated in vitro by ShlB and complemented by ShlA16.

Chromosome Deletion↗
PubMed2003

Severe soccer injuries in amateurs.

OBJECTIVES: To ascertain the number and type of severe soccer injuries admitted to King Edward Hospital in South Africa over 42 months. METHODS: This was a retrospective study of all patients admitted for treatment or observation to the orthopaedic unit only. Patients treated as outpatients, irrespective of severity, are also presented for comparison. RESULTS: Thirty two patients were admitted with severe injuries. The injuries included 18 fractures of the tibial and femoral shaft. Two tibial shaft fractures were compound. Four tibial plateau fractures and five epiphyseal injuries were identified. One patient had a fracture-dislocation of the hip. One patient with a popliteal artery injury presented 48 hours after the injury had occurred. He had an above knee amputation. In the same period 122 patients were treated as outpatients. The types of injury in this group were similar to soccer injuries reported in other countries. CONCLUSIONS: Very serious injuries are sustained by casual soccer players in South Africa. Urgent measures need to be taken to prevent such injuries.

Adolescent↗
PubMed1975

Dr. Ward's Case.

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Animals↗