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Antimicrobial Susceptibility Patterns among Viridans Group Streptococcal Isolates from Infective Endocarditis Patients from 1971 to 1986 and 1994 to 2002. Rajesh M. Prabhu, 2004.To determine whether changes in antimicrobial resistance have occurred among viridans group streptococci, we retrospectively examined 50 viridans group streptococcal isolates recovered from patients with infective endocarditis over 3 decades . Resistance rates (percent resistant isolates 1971 to 1986 and 1994 to 2002) were as follows: levofloxacin, 0 and 9; penicillin and clindamycin, 0 and 4; and erythromycin and azithromycin, 11 and 26, respectively . Investigation of Spa Pools Associated with Lung Disorders Caused by Mycobacterium avium Complex in Immunocompetent Adults. Richard Lumb, 2004.Three cases of Mycobacterium avium complex-related lung disorders were associated with two poorly maintained spa pools by genotypic investigations . Inadequate disinfection of the two spas had reduced the load of environmental bacteria to less than 1 CFU/ml but allowed levels of M . avium complex of 4.3 x 104 and 4.5 x 103 CFU/ml . Persistence of the disease-associated genotype was demonstrated in one spa pool for over 5 months until repeated treatments with greater than 10 mg of chlorine per liter for 1-h intervals eliminated M . avium complex from the spa pool . A fourth case of Mycobacterium avium complex-related lung disease was associated epidemiologically but not genotypically with another spa pool that had had no maintenance undertaken . This spa pool contained low numbers of mycobacteria by smear and was culture positive for M . avium complex, and the nonmycobacterial organism count was 5.2 x 106 CFU/ml . Public awareness about the proper maintenance of private (residential) spa pools must be promoted by health departments in partnership with spa pool retailers . Genes of De Novo Pyrimidine Biosynthesis from the Hyperthermoacidophilic Crenarchaeote Sulfolobus acidocaldarius: Novel Organization in a Bipolar Operon. Thia-Lin Thia-Toong, 2002.Sequencing a 8,519-bp segment of the Sulfolobus acidocaldarius genome revealed the existence of a tightly packed bipolar pyrimidine gene cluster encoding the enzymes of de novo UMP synthesis . The G+C content of 35.3% is comparable to that of the entire genome, but intergenic regions exhibit a considerably lower percentage of strong base pairs . Coding regions harbor the classical excess of purines on the coding strand, whereas intergenic regions do not show this bias . Reverse transcription-PCR and primer extension experiments demonstrated the existence of two polycistronic messengers, pyrEF-orf8 and pyrBI-orf1-pyrCD-orf2-orf3-orf4, initiated from a pair of divergent and partially overlapping promoters . The gene order and the grouping in two wings of a bipolar operon constitute a novel organization of pyr genes that also occurs in the recently determined genome sequences of Sulfolobus solfataricus P2 and Sulfolobus tokodaii strain 7; the configuration appears therefore characteristic of Sulfolobus . The quasi-leaderless pyrE and pyrB genes do not bear a Shine-Dalgarno sequence, whereas the initiation codon of promoter-distal genes is preceded at an appropriate distance by a sequence complementary to the 3' end of 16S rRNA . The polycistronic nature of the pyr messengers and the existence of numerous overlaps between contiguous open reading frames suggests the existence of translational coupling . pyrB transcription was shown to be approximately twofold repressed in the presence of uracil . The mechanism underlying this modulation is as yet unknown, but it appears to be of a type different from the various attenuation-like mechanisms that regulate pyrB transcription in bacteria . In contrast, the pyrE-pyrB promoter/control region harbors direct repeats and imperfect palindromes reminiscent of target sites for the binding of a hypothetical regulatory protein(s) . Integrative Genetic Element That Reverses the Usual Target Gene Orientation. Sihui Zhao, 2002.A genetic element integrating site specifically into a prokaryotic gene usually carries a copy of the 3' portion of that gene that restores the active gene even as the original is disrupted . A cryptic element in Mesorhizobium loti instead carries a copy of the 5' end of the tRNA gene into which it integrated . This has implications for the evolution of new integrase-site combinations . Transcriptional Pausing in the Bacillus subtilis pyr Operon In Vitro: a Role in Transcriptional Attenuation?. Hesheng Zhang, 2003.The genes encoding the enzymes of pyrimidine nucleotide biosynthesis (pyr genes) are regulated in Bacillus subtilis and many other bacterial species by transcriptional attenuation . When UMP or UTP is bound to the PyrR regulatory protein, it binds to pyr mRNA at specific sequences and secondary structures in the RNA . Binding to this site prevents formation of an antiterminator stem-loop in the RNA and permits formation of a downstream terminator, leading to reduced expression of the pyr genes lying downstream from the terminator . The functioning of several other transcriptional attenuation systems has been shown to involve transcriptional pausing; this observation stimulated us to use single-round transcription of pyr genes to test for formation of paused transcripts in vitro . Using templates with each of the three known B . subtilis pyr attenuation sites, we identified one major pause site in each in which the half-life of the paused transcript was increased four- to sixfold by NusA . In each case pausing at the NusA-stimulated site prevented formation of a complete antiterminator stem-loop, while it resulted in increased time for a PyrR binding loop to form and for PyrR to bind to this loop . Thus, the pausing detected in vitro is potentially capable of playing a role in establishing the correct timing for pyr attenuation in vivo . With two of three pyr templates the combination of NusA with PyrR markedly stimulated termination of transcription at the normal termination sites . This suggests that NusA, by stabilizing pausing, plays a role in termination of pyr transcription in vivo . Prokaryotic Development: Emerging Insights. Lee Kroos, 2003.
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