Comparison of high and low doses of trimethoprim-sulfamethoxazole for primary prevention of toxoplasmic encephalitis in human immunodeficiency virus-infected patients. (65/3022)

To evaluate the influence of the dose of co-trimoxazole prophylaxis on the risk of toxoplasmosis in human immunodeficiency virus (HIV)-infected patients, we performed a nested case-control study of 32 patients with toxoplasmosis (case patients) and 64 patients without toxoplasmosis (control patients) who were matched by CD4 cell count and Toxoplasma gondii serostatus; these patients were from a cohort of 521 HIV-infected patients who underwent a diagnostic neuroimaging study between March 1993 and January 1997. Twenty-seven (84.4%) of 32 case patients and 33 (51.6%) of 64 control patients received low doses of co-trimoxazole, a finding associated with an adjusted odds ratio (OR) of 9.36 (95% confidence interval [CI], 2.05-42.75) and indicating 89% protective efficacy for high doses. Fifteen (46.9%) of 32 case patients and 16 (25%) of 64 control patients were exposed to rifampin (adjusted OR, 3.38; 95% CI, 1.08-10.61). These results indicate that high doses of co-trimoxazole appear to be more effective than low doses for lowering the risk of toxoplasmosis in HIV-infected patients and that rifampin therapy may reduce the efficacy of co-trimoxazole.  (+info)

Mycobacterium ulcerans infection (Buruli ulcer): first reported case in a traveler. (66/3022)

A chronic, painless sore developed over a 2-month period on the left calf of a Canadian man traveling for 8 months in Africa. A presumptive diagnosis of a Mycobacterium spp. infection was made despite initially negative biopsy and culture results, after failure of several courses of anti-bacterial antibiotics. Mycobacterium ulcerans was eventually isolated and the lesion progressed despite treatment with multiple anti-mycobacterial agents. The lesion finally responded to wide and repeated excision, aggressive treatment with anti-mycobacterial antibiotics, and split-thickness skin grafting. The isolation and treatment of this unusual organism are discussed.  (+info)

Regulatory features of transcription in isolated mitochondria from Artemia franciscana embryos. (67/3022)

Optimal conditions were developed for an in organello transcriptional run-on assay using mitochondria isolated from Artemia franciscana embryos to investigate potential regulatory features of RNA synthesis under conditions of anoxia-induced quiescence. Transcription is not dependent on oxidative phosphorylation for maximal activity when exogenous ATP is available. Bona fide transcription products, as assessed by hybridization with specific mitochondrial cDNAs from A. franciscana, are produced in an inhibitor-sensitive manner. Transcription rate measured at pH 7.9 is reduced 80% when pH is lowered to 6.3, a pH range that mimics the in vivo change seen on exposure of embryos to anoxia. The proton sensitivity of mitochondrial RNA synthesis may provide a mechanism to depress this significant energy expenditure during quiescence. The influence of nucleotide concentration on kinetics is complicated by an interdependence among nucleotide species. ATP inhibition observed at subsaturating UTP concentrations is relieved when UTP is at saturating, physiologically relevant levels. Taken together, these data suggest that local (versus nuclear mediated) control is important in dictating mitochondrial transcription during rapid modulations in gene expression, such as those observed under anoxia-induced quiescence.  (+info)

The multisubunit chloroplast RNA polymerase A from mustard (Sinapis alba L.). Integration of a prokaryotic core into a larger complex with organelle-specific functions. (68/3022)

We previously identified two multisubunit plastid RNA polymerases termed A and B. The B enzyme has a bacterial-type polypeptide composition and is sensitive to the prokaryotic transcription inhibitor rifampicin (Rif); the A enzyme has a more complex subunit structure and is Rif-resistant. Here we report results of N-terminal sequencing and MS carried out with the A enzyme, which establish that the latter contains rpo gene products and is structurally related to the B enzyme. Furthermore, evidence is provided that the A enzyme can be converted into a Rif-sensitive enzyme form in a phosphorylation-dependent manner in vitro by a treatment that results in depletion of a beta-like subunit. Database searches using sequence information derived from additional polypeptides that are present in purified A preparations revealed sequence similarity with chloroplast proteins involved in RNA processing and redox control. This proteomics approach thus points to the complexity of the chloroplast transcription apparatus and its interconnections with post-transcriptional and signalling mechanisms.  (+info)

Increased levels of dihydrofolate reductase in rifampin-resistant mutants of Bacillus subtilis. (69/3022)

Several independent, spontaneous rifampin-resistant mutants of Bacillus subtilis were isolated and found to have an increased resistance to trimethoprim, an inhibitor of dihydrofolate reductase. This increased resistance in the rif mutants was the result of a specific threefold increase in the activity of dihydrofolate reductase, since six other enzymes examined remained unchanged. This increased level of dihydrofolate reductase and the trimethoprim resistance were cotransformed (100%) with the rif marker. These results suggest that the RNA polymerase is altered in its recognition of the gene that specifies dihydrofolate reductase.  (+info)

Role of the tetraheme cytochrome CymA in anaerobic electron transport in cells of Shewanella putrefaciens MR-1 with normal levels of menaquinone. (70/3022)

Shewanella putrefaciens MR-1 possesses a complex electron transport system which facilitates its ability to use a diverse array of compounds as terminal electron acceptors for anaerobic respiration. A previous report described a mutant strain (CMTn-1) deficient in CymA, a tetraheme cytochrome c. However, the interpretation of the electron transport role of CymA was complicated by the fact that CMTn-1 was also markedly deficient in menaquinones. This report demonstrates that the depressed menaquinone levels were the result of the rifampin resistance phenotype of the parent of CMTn-1 and not the interruption of the cymA gene. This is the first report of rifampin resistance leading to decreased menaquinone levels, indicating that rifampin-resistant strains should be used with caution when analyzing electron transport processes. A site-directed gene replacement approach was used to isolate a cymA knockout strain (MR1-CYMA) directly from MR-1. While MR1-CYMA retained menaquinone levels comparable to those of MR-1, it lost the ability to reduce iron(III), manganese(IV), and nitrate and to grow by using fumarate as an electron acceptor. All of these functions were restored to wild-type efficacy, and the presence of the cymA transcript and CymA protein was also restored, by complementation of MR1-CYMA with the cymA gene. The requirement for CymA in anaerobic electron transport to iron(III), fumarate, nitrate, and manganese(IV) is therefore not dependent on the levels of menaquinone in these cells. This represents the first successful use of a suicide vector for directed gene replacement in MR-1.  (+info)

Accumulation of rifampicin by Mycobacterium aurum, Mycobacterium smegmatis and Mycobacterium tuberculosis. (71/3022)

The characteristics of the accumulation of 2 mg/L [(14)C]rifampicin by wild-type strains of Mycobacterium aurum (A(+)), Mycobacterium smegmatis (mc(2)155) and Mycobacterium tuberculosis (H37Rv) were determined. After 10 min exposure M. aurum had accumulated 220 ng rifampicin/mg cells, M. smegmatis had accumulated 120 ng rifampicin/mg cells and M. tuberculosis had accumulated 154 ng rifampicin/mg cells. A steady-state concentration (SSC) of rifampicin was accumulated rapidly by M. aurum and M. tuberculosis within minutes of drug exposure, unlike M. smegmatis, which accumulated rifampicin more slowly. With an increase in the concentration of rifampicin from 0.12 mg/L to 2 mg/L there was an increase in the concentration of rifampicin accumulated by M. tuberculosis, with no detectable loss of viability over the 20 min of the accumulation experiment. With an increase in temperature there was also an increase in the concentration of rifampicin accumulated by M. tuberculosis; between 15 and 30 degrees C the increase was linear. For all three species sub-inhibitory concentrations of ethambutol increased the concentration of rifampicin accumulated. However, both growth and accumulation of rifampicin were lower in the presence of 0.05% Tween 80. Accumulation of rifampicin by M. smegmatis was unaffected by the presence of the proton motive force inhibitor, 2,4-dinitrophenol (1 mM), whether added before or after the addition of rifampicin to the mycobacterial culture. For all three species, the Gram-positive bacterial efflux inhibitor reserpine (20 mg/L) slightly increased the SSC of rifampicin, but the increase was not statistically significant. Addition of glucose to energize a putative efflux pump had little effect on the accumulation of rifampicin in the presence or absence of reserpine for M. tuberculosis; however, for M. aurum and M. smegmatis the reserpine effect was abolished by the addition of glucose. These data suggest that rifampicin may be removed from wild-type mycobacteria by efflux, but that the pump(s) is expressed at low level.  (+info)

In vitro activity of ciprofloxacin, sparfloxacin, ofloxacin, amikacin and rifampicin against Ghanaian isolates of Mycobacterium ulcerans. (72/3022)

MICs of ciprofloxacin, sparfloxacin, ofloxacin, amikacin and rifampicin were determined for 14 primary clinical isolates and three reference isolates of Mycobacterium ulcerans by modifying a standard agar dilution method for testing Mycobacterium tuberculosis sensitivity. All these antimicrobials were active against every isolate of M. ulcerans. Sparfloxacin exhibited the highest activity and ofloxacin was the least effective. Rifampicin exhibited the broadest range of activity.  (+info)