|
|
|
|
|
|
Clinical Emergence of Entecavir-Resistant Hepatitis B Virus Requires Additional Substitutions in Virus Already Resistant to Lamivudine. D. J. Tenney, 2004.Entecavir (ETV) exhibits potent antiviral activity in patients chronically infected with wild-type or lamivudine (3TC)-resistant (3TCr) hepatitis B virus (HBV) . Among the patients treated in phase II ETV clinical trials, two patients for whom previous therapies had failed exhibited virologic breakthrough while on ETV . Isolates from these patients (arbitrarily designated patients A and B) were analyzed genotypically for emergent substitutions in HBV reverse transcriptase (RT) and phenotypically for reduced susceptibility in cultures and in HBV polymerase assays . After 54 weeks of 3TC therapy, patient A (AI463901-A) received 0.5 mg of ETV for 52 weeks followed by a combination of ETV and 100 mg of 3TC for 89 weeks . Viral rebound occurred at 133 weeks after ETV was started . The 3TCr RT substitutions rtV173L, rtL180M, and rtM204V were present at study entry, and the additional substitutions rtI169T and rtM250V emerged during ETV-3TC combination treatment . Reduced ETV susceptibility in vitro required the rtM250V substitution in addition to the 3TCr substitutions . For liver transplant patient B (AI463015-B), previous famciclovir, ganciclovir, foscarnet, and 3TC therapies had failed, and RT changes rtS78S/T, rtV173L, rtL180M, rtT184S, and rtM204V were present at study entry . Viral rebound occurred after 76 weeks of therapy with ETV at 1.0 mg, with the emergence of rtT184G, rtI169T, and rtS202I substitutions within the preexisting 3TCr background . Reduced susceptibility in vitro was highest when both the rtT184G and the rtS202I changes were combined with the 3TCr substitutions . In summary, infrequent ETV resistance can emerge during prolonged therapy, with selection of additional RT substitutions within a 3TCr HBV background, leading to reduced ETV susceptibility and treatment failure . Culture-Independent Analysis of Fecal Enterobacteria in Environmental Samples by Single-Cell mRNA Profiling. Han Chen, 2004.A culture-independent method called mRNA profiling has been developed for the analysis of fecal enterobacteria and their physiological status in environmental samples . This taxon-specific approach determines the single-cell content of selected gene transcripts whose abundance is either directly or inversely proportional to growth state . Fluorescence in situ hybridization using fluorochrome-labeled oligonucleotide probes was used to measure the cellular concentration of fis and dps mRNA . Relative levels of these transcripts provided a measure of cell growth state and the ability to enumerate fecal enterobacterial cell number . Orthologs were cloned by inverse PCR from several major enterobacterial genera, and probes specific for fecal enterobacteria were designed using multiple DNA sequence alignments . Probe specificity was determined experimentally using pure and mixed cultures of the major enterobacterial genera as well as secondary treated wastewater samples seeded with pure culture inocula . Analysis of the fecal enterobacterial community resident in unseeded secondary treated wastewater detected fluctuations in transcript abundance that were commensurate with incubation time and nutrient availability and demonstrated the utility of the method using environmental samples . mRNA profiling provides a new strategy to improve wastewater disinfection efficiency by accelerating water quality analysis . Legume Symbiotic Nitrogen Fixation by ß-Proteobacteria Is Widespread in Nature. Wen-Ming Chen, 2003.Following the initial discovery of two legume-nodulating Burkholderia strains (L . Moulin, A . Munive, B . Dreyfus, and C. Boivin-Masson, Nature 411:948-950, 2001), we identified as nitrogen-fixing legume symbionts at least 50 different strains of Burkholderia caribensis and Ralstonia taiwanensis, all belonging to the ß-subclass of proteobacteria, thus extending the phylogenetic diversity of the rhizobia . R . taiwanensis was found to represent 93% of the Mimosa isolates in Taiwan, indicating that ß-proteobacteria can be the specific symbionts of a legume . The nod genes of rhizobial ß-proteobacteria (ß-rhizobia) are very similar to those of rhizobia from the  -subclass (-rhizobia), strongly supporting the
hypothesis of the unique origin of common nod genes . The
ß-rhizobial nod genes are located on a 0.5-Mb plasmid,
together with the nifH gene, in R.
taiwanensis and Burkholderia phymatum.
Phylogenetic analysis of available nodA gene sequences
clustered ß-rhizobial sequences in two nodA lineages
intertwined with
-rhizobial sequences . On the other hand, the
ß-rhizobia were grouped with free-living nitrogen-fixing
ß-proteobacteria on the basis of the nifH phylogenetic
tree . These findings suggest that ß-rhizobia evolved from
diazotrophs through multiple lateral nod gene
transfers .
Distribution of the Coenzyme M Pathway of Epoxide Metabolism among Ethene- and Vinyl Chloride-Degrading Mycobacterium Strains. Nicholas V. Coleman , 2003.An epoxyalkane:coenzyme M (CoM) transferase (EaCoMT) enzyme was recently found to be active in the aerobic vinyl chloride (VC) and ethene assimilation pathways of Mycobacterium strain JS60 . In the present study, EaCoMT activity and genes were investigated in 10 different mycobacteria isolated on VC or ethene from diverse environmental samples . In all cases, epoxyethane metabolism in cell extracts was dependent on CoM, with average specific activities of EaCoMT between 380 and 2,910 nmol/min/mg of protein . PCR with primers based on conserved regions of EaCoMT genes from Mycobacterium strain JS60 and the propene oxidizers Xanthobacter strain Py2 and Rhodococcus strain B-276 yielded fragments (834 bp) of EaCoMT genes from all of the VC- and ethene-assimilating isolates . The Mycobacterium EaCoMT genes form a distinct cluster and are more closely related to the EaCoMT of Rhodococcus strain B-276 than that of Xanthobacter strain Py2 . The incongruence of the EaCoMT and 16S rRNA gene trees and the fact that isolates from geographically distant locations possessed almost identical EaCoMT genes suggest that lateral transfer of EaCoMT among the Mycobacterium strains has occurred . Pulsed-field gel electrophoresis revealed large linear plasmids (110 to 330 kb) in all of the VC-degrading strains . In Southern blotting experiments, the strain JS60 EaCoMT gene hybridized to many of the plasmids . The CoM-mediated pathway of epoxide metabolism appears to be universal in alkene-assimilating mycobacteria, possibly because of plasmid-mediated lateral gene transfer .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
