Evolution of antibiotic resistance genes: the DNA sequence of a kanamycin resistance gene from Staphylococcus aureus

The kanamycin resistance gene from Staphylococcus aureus has been sequenced and its structure compared with similar genes isolated from Streptomyces fradiae and from two transposons, Tn5 and Tn903, originally isolated from Klebsiella pneumoniae and Salmonella typhimurium, respectively. The genes are all homologous but, since their common ancestor, have undergone extensive divergence, with more than 43% divergence between the closest pair. The phylogeny of the genes cannot be made congruent to the phylogeny of the taxa from which they were isolated without requiring rather improbable differences in rates. One is therefore led to conclude that there have been multiple occurrences of gene transfer between these species. Thus, although they are homologous, they are neither orthologous nor paralogous. It is suggested that homologous genes of this type be called xenologous.      

Electronic transitions in molecules in static external fields. I. Indole and Trp-59 in ribonuclease T1

Electronic transition properties of indole perturbed by its environment were calculated by use of quantum-mechanical semi-empirical numerical methods. The environment was represented by a discrete set of charges placed at different positions around the indole ring. Wavelength shifts and transition intensity changes in indole were evaluated for several, specifically modeled geometries of external charges. This methodology was employed to estimate the extent of spectroscopic changes induced by small nonprotein polar species on the Trp-59 residue in the anisotropic environment of the protein ribonuclease T1. The geometry of the residue environment was obtained from dynamically equilibrated X-ray crystallographic data of the protein.     

Discriminating the loosening behaviour of cemented hip prostheses using measurements of migration and inducible displacement.

In vitro pre-clinical tests of hip prostheses have not yet been developed to the extent that inferior prostheses can be 'screened-out' prior to animal or clinical trials. This paper reports the experimental part of a project to develop a pre-clinical testing platform for cemented femoral hip implants. It is based on the clinical observation (K?rrholm et al. JBJS, 76B (1994) 912-916) that higher subsidence (distal migration) correlates with early revision of hip prostheses. A protocol to measure the relative movement between implant and bone was designed to test whether or not such a measurement, if made in a laboratory, could discriminate between hip prostheses. The protocol was applied to the Lubinus SPII prosthesis (W. Link, Germany) and a Müller Curved Stem (JRI Ltd., UK)-these prostheses were chosen because they are known to have different loosening rates in vivo. Five prostheses of each design were tested. The migration, the rate-of-migration, and the inducible displacement of each prosthesis was recorded over two million cycles of loading.For each implant, rapid initial migration was found, followed by a period of steady-state migration. In the majority of cases, the prostheses migrated medially, distally and posteriorly. On average, the Lubinus migrated less than the Müller in all directions. The average Lubinus migration was less than half that of the Müller, and this difference was significant at a level of p=0.05. Inducible displacement was greater for the Müller compared to the Lubinus. Furthermore, the inducible displacement decreased over time for the majority of Lubinus prostheses whereas it increased over time for the majority of the Müller prostheses leading to the conclusion that a rapid pre-clinical test based on measurement of inducible displacement may be possible.     

Sterilisation of explants and cultures with sodium dichloroisocyanurate

The effectiveness of Sodium dichloroisocyanurate as a disinfectant for micropropagated plants was assessed. Analysis of the microbial flora of micropropagated plants showed a wide range of bacteria with predominantly Pseudomonas, Xanthomonas and Actinomycetes. Sodium dichloroisocyanurate was highly stable both as preprepared tablets and as solutions maintained at room temperature. Sterilisation of a range of plants which were heavily contaminated with bacteria was examined. Phytotoxicity was generally low and restricted to old leaves and cut surfaces. Solutions of Sodium dichloroisocyanurate were more effective at high concentrations (5000 ppm) than a commercially available bleach for disinfection of shoot cultures. Sodium dichloroisocyanurate was also used at low concentrations (300 ppm) for longer periods (24 h–48 h) to disinfect shoot explants from the field, and was at least as effective for sterilisation as a combination of Mercuric Chloride and Calcium hypochlorite.Abbreviations NaDCC Sodium Dichloroisocyanurate