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PubMed1991

Molecular and genetic analysis of the gene encoding the Saccharomyces cerevisiae strand exchange protein Sep1.

Vegetatively grown Saccharomyces cerevisiae cells contain an activity that promotes a number of homologous pairing reactions. A major portion of this activity is due to strand exchange protein 1 (Sep1), which was originally purified as a 132,000-Mr species (R. Kolodner, D. H. Evans, and P. T. Morrison, Proc. Natl. Acad. Sci. USA 84:5560-5564, 1987). The gene encoding Sep1 was cloned, and analysis of the cloned gene revealed a 4,587-bp open reading frame capable of encoding a 175,000-Mr protein. The protein encoded by this open reading frame was overproduced and purified and had a relative molecular weight of approximately 160,000. The 160,000-Mr protein was at least as active in promoting homologous pairing as the original 132,000-Mr species, which has been shown to be a fragment of the intact 160,000-Mr Sep1 protein. The SEP1 gene mapped to chromosome VII within 20 kbp of RAD54. Three Tn10LUK insertion mutations in the SEP1 gene were characterized. sep1 mutants grew more slowly than wild-type cells, showed a two- to fivefold decrease in the rate of spontaneous mitotic recombination between his4 heteroalleles, and were delayed in their ability to return to growth after UV or gamma irradiation. Sporulation of sep1/sep1 diploids was defective, as indicated by both a 10- to 40-fold reduction in spore formation and reduced spore viability of approximately 50%. The majority of sep1/sep1 diploid cells arrested in meiosis after commitment to recombination but prior to the meiosis I cell division. Return-to-growth experiments showed that sep1/sep1 his4X/his4B diploids exhibited a five- to sixfold greater meiotic induction of His+ recombinants than did isogenic SEP1/SEP1 strains. sep1/sep1 mutants also showed an increased frequency of exchange between HIS4, LEU2, and MAT and a lack of positive interference between these markers compared with wild-type controls. The interaction between sep1, rad50, and spo13 mutations suggested that SEP1 acts in meiosis in a pathway that is parallel to the RAD50 pathway.

Amino Acid Sequence↗

PubMed1979

Escherichia coli mutant strain with altered expression of the tryptophan operon: isolation and preliminary characterization.

From a strain of Escherichia coli with two copies of the tryptophan (trp) operon and one copy of the lactose (lac) operon, under control of one of the trp regulatory elements, we have isolated a mutant which does not grow in a medium containing 19 amino acids, unless tryptophan is added, and which cannot ferment lactose. The apparent pleiotropic nature of the mutation(s) is indicated by the very slow growth of mutant bacteria on minimal-medium agar supplemented with glucose and tryptophan. The amount of the trp enzymes (anthranilate synthetase and tryptophan synthetase) and trp messenger ribonucleic acid is reduced several-fold in the mutant compared to the isogenic wild-type strain, whereas the enzymes tryptophanyl-transfer ribonucleic acid synthetase and glucose 6-phosphate dehydrogenase remain the same. The incorporation of radioactive label into pulse-labeled but not into stable ribonucleic acid is significantly lower. Our results suggest that in the mutant organism the control of transcription of some operons, including the trp operon, is modified. An alternative explanation is that mutant bacteria contain a ribonuclease with increased activity for some messenger ribonucleic acid species.

Anthranilate Synthase↗

PubMed2002

Reconstruction of peripheral nerves using acellular nerve grafts with implanted cultured Schwann cells.

The bridging of nerve gaps is still one of the major problems in peripheral nerve surgery. The present experiment describes our attempt to engineer different biologic nerve grafts in a rat sciatic nerve model: cultured isogenic Schwann cells were implanted into 2-cm autologous acellular nerve grafts or autologous predegenerated nerve grafts. Autologous nerve grafts and predegenerated or acellular nerve grafts without implanted Schwann cells served as controls. The regenerated nerves were assessed histologically and morphometrically after 6 weeks. Predegenerated grafts showed results superior in regard to axon count and histologic appearance in comparison to standard grafts and acellular grafts. The acellular nerve grafts showed the worst histologic picture, but axon counts were in the range of standard grafts. The implantation of Schwann cells did not yield significant improvements in any group. In conclusion, the status of activation of Schwann cells and the stadium of Wallerian degeneration in a nerve graft might be key factors for regeneration, rather than total number of Schwann cells. Predegenerated nerve grafts are therefore superior to standard grafts in the rat model. Acellular grafts are able to bridge nerve gaps of up to 2 cm in the rat model, but even the addition of cultivated Schwann cells did not lead to results as good as in the group with autologous nerve grafts.

Animals↗

PubMed2004

Local application of rapamycin inhibits neointimal hyperplasia in experimental vein grafts.

BACKGROUND: Rapamycin is an immunosuppressive agent which also exhibits marked antiproliferative properties. Rapamycin coated stents have been demonstrated to suppress restenosis in experimental and clinical studies of percutaneous coronary catheter intervention. We investigated whether rapamycin can reduce neointima formation in a mouse model of vein graft disease. METHODS: C57BL6J mice underwent interposition of the inferior vena cava from isogenic donor mice into the common carotid artery using a previously described cuff technique. In the treatment group, 100 microg or 200 microg of rapamycin was applied locally in pluronic gel. The control group did not receive local treatment. Grafts were harvested at 1, 2, 4, and 6 weeks and underwent morphometric analysis as well as immunohistochemical analysis. RESULTS: In grafted veins without treatment (controls), median intimal thickness was 9.6 (6.4 to 29)microm, 11.9 (7.9 to 39.9)microm, 46.6 (12.4 to 57.7)microm, and 57.5 (32.5 to 71.1)microm after 1, 2, 4, and 6 weeks, respectively. Treatment with 100 microg or 200 microg rapamycin showed a dose dependent reduction of intimal thickness. In the 200 microg rapamycin treatment group the intimal thickness was 4.3 (3.4 to 5.6)microm, 3.8 (3.2 to 6.3)microm, 17.1 (4.8 to 63)microm, and 33.9 (11.3 to 80.3)microm after 1, 2, 4, and 6 weeks, respectively. This difference of intimal thickness of 200 microg treated animals compared with controls was statistically significant at 1 and 2 weeks. Immunohistochemically the reduction of intimal thickness was associated with a decreased amount of infiltration of CD-8 positive cells and a decreased amount of metallothionein positive cells in the rapamycin treated grafts. CONCLUSIONS: We conclude that perivascular application of rapamycin inhibits neointimal hyperplasia of vein grafts in a mouse model. These results suggest that rapamycin may have a therapeutic potential for the treatment of vein graft disease.

Animals↗

PubMed2006

Role of the Fancg gene in protecting cells from particulate chromate-induced chromosome instability.

Particulate hexavalent chromium (Cr(VI)) is a known human lung carcinogen. Cr(VI)-induced tumors exhibit chromosome instability (CIN), but the mechanisms underlying these effects are unknown. We investigated a possible role for the Fanconi anemia (FA) pathway in particulate Cr(VI)-induced chromosomal damage by focusing on the Fancg gene, which plays an important role in cellular resistance to DNA interstrand crosslinks. We used the isogenic Chinese hamster ovary (CHO) KO40 fancg mutant compared with parental and gene-complemented cells. We found that fancg cells treated with lead chromate had lower intracellular Cr ion levels than control cell lines. Accounting for differences of Cr ion levels between cell lines, we discovered that fancg cells treated with lead chromate had increased cytotoxicity and chromosomal aberrations, which was not observed after restoring the Fancg gene. Chromosomal damage was manifest as increased total chromosome damage and percent metaphases with damage, specifically an increase in chromatid and isochromatid breaks. We conclude that Fancg protects cells from particulate Cr(VI)-induced cytotoxicity and chromosome damage, which is consistent with the known sensitivity of fancg cells to crosslinking damage and the ability of Cr(VI) to produce crosslinks.

Animals↗

PubMed1999

Starvation-associated mutagenesis in yeast Saccharomyces cerevisiae is affected by Ras2/cAMP signaling pathway.

The number of revertants with restored ability to form colony increases in a time-dependent manner during long-term selective starvation of dense mutant microbial cultures. This is due to starvation-associated (also called adaptive) mutations that arise in a replication independent manner. Here we report that in Saccharomyces cerevisiae the frequency of starvation-associated reversions of mutant genes whose products are necessary for amino acids biosynthesis are influenced by Ras2/cAMP signaling pathway. This signaling pathway is a yeast general regulatory pathway involved in nutritional sensing, UV response, sporulation control and life span control and its changes are manifested in both, cell cycle and life cycle. Inactivation of the RAS2 gene causes an increase in number of starvation-associated revertants in comparison to an isogenic wild type strain and a strain with constitutively activated Ras2/cAMP signaling pathway. Therefore, we suggest that starvation-associated mutagenesis is different from spontaneous mutagenesis and is related to the cellular capacity to adopt distinct physiological states in response to environmental signals.

Culture Media↗

PubMed1999

Connective tissue responses to calcium hydroxide-based root canal medicaments.

AIM: The objective of the present study was to evaluate the tissue inflammatory response induced by calcium hydroxide pastes, with or without paramonochlorophenol and camphor. METHODOLOGY: Isogenic BALB/c mice were inoculated into the subcutaneous tissue with either 0.1 mL of a suspension of Calen, Calen with camphorated paramonochlorophenol, Calen with paramonochlorophenol, Calasept paste or phosphate-buffered saline (control). After 6, 12 and 24 h and 2, 3, 5, 7 and 15 days, three animals in each group were sacrificed and the excised lesions processed for histopathological evaluation of the inflammatory response. Events monitored and graded included the assessment of vascular congestion, oedema, haemorrhage, inflammatory infiltrate, necrosis and tissue repair. RESULTS: The pastes induced an inflammatory response at every observation period, although the intensity, duration and extension of inflammation varied. Calen paste always produced an initial short-term inflammatory response whilst the other pastes produced extended reactions. All pastes allowed repair to take place by the end of the experimental period, although the speed of this process varied between the materials. Calen presented the best biocompatibility; the phenolic compound caused greater tissue response, which was even more severe in the absence of camphor. Calasept paste was damaging and the repair process slower. CONCLUSIONS: All calcium hydroxide formulations caused an inflammatory response. The severity and longevity of the responses varied between pastes as a result of the various antiseptic agents. Although irritating, repair was apparent with all formulations.

Animals↗

PubMed2002

The neuA/flmD gene cluster of Helicobacter pylori is involved in flagellar biosynthesis and flagellin glycosylation.

Helicobacter pylori possesses a gene (HP0326/JHP309) homologous to neuA of other bacteria, encoding a cytidyl monophosphate-N-acetylneuraminic acid synthetase-homologous enzyme in its N-terminal portion. We analysed the function of this gene, which is controlled by a flagellar class 2 sigma(54) promoter, in flagellar biosynthesis. HP0326/JHP309 actually represents a bicistronic operon consisting of a neuA and a flmD-like putative glycosyl transferase gene. An isogenic flmD mutant synthesized basal bodies but no filaments, was non-motile, and expressed severely reduced amounts of a FlaA flagellin of reduced molecular mass. FlaA flagellin was found to be glycosylated in its exported form within the flagellar filament, but not inside the cytoplasm. Glycosylated FlaA was not detectable in the flmD mutant. Together with other genes in the H. pylori genome, a proposed function of the neuA/flmD gene products could be to provide a pathway for glycosylation of flagellin and other extracytoplasmic molecules during type III secretion.

Blotting, Western↗

PubMed2001

Capsule production and growth phase influence binding of complement to Staphylococcus aureus.

Complement-mediated opsonization of bacteria by C3 binding is an important component of the host innate immune system. Little information is available concerning the interaction between complement proteins and capsule type 5 and 8 Staphylococcus aureus strains, even though these isolates are responsible for approximately 70% of human staphylococcal infections. To investigate the importance of an intact complement pathway in an experimental staphylococcal infection, control and C3-depleted mice were challenged intravenously with 10(7) CFU of a serotype 5 S. aureus isolate. Whereas only 8% of the control mice succumbed to the infection, 64% of the complemented-depleted animals died. In vitro parameters of C3 binding to two heavily encapsulated (CP++) strains, three encapsulated (CP+) strains, and an isogenic capsule-negative (CP-) mutant were examined. The alternative pathway contributed 90% of C3 binding in 20% serum at 30 min, whereas it accounted for only 13% of C3 binding in 2% serum. Stationary-phase organisms bound only 10% as much C3 as mid-log-phase organisms; this was only in part due to capsule. When the S. aureus strains were cultivated on solid medium, the CP++ isolates bound 50% less C3 than CP+ strains; a CP+ strain bound 42% less C3 than the CP- mutant. Both C3b and iC3b fragments of C3 bound to S. aureus cells, and about one-third of the bound C3 was shed from the staphylococcal surface as iC3b, regardless of the CP phenotype of the strain. Thus, the phase of growth and presence of capsule are critical to opsonization.

Agammaglobulinemia↗

PubMed2004

AFLP targeting of the 1-cM region conferring the vrs1 gene for six-rowed spike in barley, Hordeum vulgare L.

Spike morphology is a key characteristic in the study of barley domestication, yield, and use. Multiple alleles at the vrs1 locus control the development and fertility of the lateral spikelets of barley. We developed five amplified fragment length polymorphism (AFLP) markers tightly linked to the vrs1 locus using well-characterized near-isogenic lines as plant materials. The AFLP markers were integrated into three different maps, in which 'Azumamugi' was used as the maternal parent. Of the three maps, Hordeum vulgare L. 'Azumamugi' x H. vulgare 'Golden Promise' showed recombination of the AFLP markers and the vrs1 locus (closest, 0.05 cM), providing the best mapping population for positional cloning of alleles at the vrs1 locus. Conversion of AFLP bands into polymorphic sequence-tagged sites (STSs) is necessary for further high-throughput genotype scoring and for bacterial artificial chromosome (BAC) library screening. We cloned and sequenced the five AFLP bands and synthesized primer pairs. PCR amplification generated DNAs of the same size from all four parental lines for each marker. Restriction endonuclease treatment of e40m36-1110/AccIII, e34m13-260/Psp1406I, e52m32-270/FokI, and e31m26-520/MnlI revealed fragment length polymorphisms between 'Azumamugi' and all the two-rowed parents. Allelism between the AFLPs and corresponding STS markers was confirmed genetically, indicating the usefulness of the STSs as genetic markers.

Alleles↗

PubMed2003

Contractile reserve and calcium regulation are depressed in myocytes from chronically unloaded hearts.

BACKGROUND: Chronic cardiac unloading of the normal heart results in the reduction of left ventricular (LV) mass, but effects on myocyte contractile function are not known. METHODS AND RESULTS: Cardiac unloading and reduction in LV mass were induced by heterotopic heart transplantation to the abdominal aorta in isogenic rats. Contractility and [Ca(2+)](i) regulation in LV myocytes were studied at both 2 and 5 weeks after transplantation. Native in situ hearts from recipient animals were used as the controls for all experiments. Contractile function indices in myocytes from 2-week unloaded and native (control) hearts were similar under baseline conditions (0.5 Hz, 1.2 mmol/L [Ca(2+)](o), and 36 degrees C) and in response to stimulation with high [Ca(2+)](o) (range 2.5 to 4.0 mmol/L). In myocytes from 5-week unloaded hearts, there were no differences in fractional cell shortening and peak-systolic [Ca(2+)](i) at baseline; however, time to 50% relengthening and time to 50% decline in [Ca(2+)](i) were prolonged compared with controls. Severe defects in fractional cell shortening and peak-systolic [Ca(2+)](i) were elicited in myocytes from 5-week unloaded hearts in response to high [Ca(2+)](o). However, there were no differences in the contractile response to isoproterenol between myocytes from unloaded and native hearts. In 5-week unloaded hearts, but not in 2-week unloaded hearts, LV protein levels of phospholamban were increased (345% of native heart values). Protein levels of sarcoplasmic reticulum Ca(2+) ATPase and the Na(+)/Ca(2+) exchanger were not changed. CONCLUSIONS: Chronic unloading of the normal heart caused a time-dependent depression of myocyte contractile function, suggesting the potential for impaired performance in states associated with prolonged cardiac atrophy.

Animals↗

PubMedDate not supplied

Glucose-insulin kinetics of the extravascular bioartificial pancreas. A study using microencapsulated rat islets.

The success of the extravascular bioartificial pancreas (BAP) is contingent on the rapid transfer of the glycemic signal across both an extravascular compartment and a semipermeable membrane and of insulin from the BAP to the recipient. To examine the possibility of microencapsulated islets such as the BAP to achieve satisfactory in vivo glucose-insulin kinetics, islets were isolated from Lewis rats, encapsulated in poly-L-lysine-alginate membranes, and isogenically transplanted into the peritoneal cavity of 14 streptozotocin induced diabetic rats. Fasting blood glucose (BG) was measured and intravenous glucose tolerance was tested at 8-10 weeks and compared with three control groups: 1) normal Lewis rats (n = 6); 2) untreated diabetic rats (n = 5); and 3) diabetic rats that received intraperitoneal implants of empty capsules (n = 4). Ten animals that received microencapsulated islets (5,271 +/- 431) promptly became normoglycemic, with a mean BG of 128 +/- 17 ng/dl 3 days after transplantation and maintained this level > 100 days. Intravenous glucose tolerance K-value for the group was 3.84 +/- 0.32 compared with 3.96 +/- 0.39 (p = 0.83) for the normal control group, and 0.60 +/- 0.12 (p < 0.01) and 0.40 +/- 0.15 (p < 0.01) for the diabetic control groups with and without empty capsules. The authors conclude from these results that, given sufficient beta-cell mass, a BAP without any vascular access can respond appropriately to an increase in blood glucose concentration, without overshoot hypoglycemia and within a lag lapse compatible with normal physiologic insulin delivery.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2004

[Identification of RAPD markers linked to the resistance gene Yr5 against wheat stripe rust with denaturing PAGE-silver staining].

RAPD analysis was performed between a near-isogenic line (NIL) Yr5/6 x Avocet S carrying the resistance gene Yr5 against wheat stripe rust and its susceptible parent Avocet S, using the Yr5 gene donor parent Triticum spelta album as control. Amplified DNA fragments were separated on 4% denaturing PAGE (polyacrylamide gel electrophoresis) and displayed by silver staining. Fifty to 100 bands were detected, 5 folds more than those revealed on agarose gels. A total of 240 random primers were screened, and 23 reproducible polymorphic DNA fragments were found, out of which 6 polymorphic bands appeared to be linked to Yr5 gene. Genetic linkage was tested on 121 segregating F2 plants derived from a cross between Avocet S and Yr5/6 x Avocet S. It was showed that the polymorphic DNA fragment S1320(207) was completely linked to Yr5 gene, and S1348(363) closely linked to Yr5 gene. The results suggested that using denaturing PAGE-silver staining could increase the level of DNA polymorphisms detected in wheat and also improve the repeatability of RAPD analysis.

Electrophoresis, Polyacrylamide Gel↗

PubMedDate not supplied

Improved recovery following posttransplant acute renal failure in rat renal isografts with an oral endothelin-A receptor antagonist.

BACKGROUND: Delayed renal function after transplantation is a strong predictor of long-term graft survival. As an increased expression of endothelin (ET) has been demonstrated during ischemia/reperfusion injury, we hypothesized that ET-A receptor blockade could improve the recovery of acute renal failure in a rat model of isogeneic kidney transplantation. METHODS: Kidneys of Fisher (F344, RT1(1v1)) rat donors flushed with cooled University of Wisconsin solution were transplanted into bilaterally nephrectomized Fisher rats. Recipient animals were treated orally either with vehicle or the selective ET-A receptor antagonist LU135252 (30 mg/kg/day p.o.) for 14 days. Unilaterally nephrectomized Fisher rats not subjected to ischemia served as controls. No immunosuppression was given. On days 2, 6 and 14, metabolic studies were performed to evaluate endogenous creatinine clearance, fractional sodium excretion, and urinary endothelin excretion. Kidneys were harvested at the end of the experiment for determination of renal ET content and immunohistochemical assessment. RESULTS: Urinary ET excretion was increased in vehicle-treated isografts compared to uninephrectomized controls after 14 days. Treatment with LU135252 resulted in a significant improvement in creatinine clearance and fractional sodium excretion to the level of uninephrectomized rats after 14 days. Isografts treated with selective ET-A receptor blockade demonstrated a marked reduction in cell surface markers for macrophages/monocytes, T cells, MHC-II, and ICAM-1. CONCLUSION: Treatment with the selective ET-A receptor antagonist LU135252 accelerates recovery of renal function after isogeneic renal transplantation and attenuates cellular graft infiltration. This effect could have major implications for the treatment of patients undergoing renal transplantation, as an improved initial renal function may delay the onset of chronic allograft rejection.

Acute Kidney Injury↗

PubMed1981

Stringent control of intermediary metabolism in Escherichia coli: pyruvate excretion by cells grown on succinate.

A large amount of pyruvate was excreted into the medium by CP78 (rel+) cells grown on succinate when they were starved for amino acids. In contrast, no such excretion was observed with CP79 (rel-) cells. This phenomenon was also seen with two other isogenic pairs of strains: NF161 (rel+) and NF162 (rel-), and 10B601 (rel+) and 10B602 (rel-). Besides succinate, L-malate, and fumarate were effective carbon sources for the excretion, but glucose, glycerol, and acetate were not. When DL-lactate was used, not only CP78 but also CP79 cells excreted pyruvate. Experiments using [1,4-14C]succinate as a carbon source revealed that pyruvate was formed by decarboxylation of one carboxyl group of succinate and that the pyruvate excretion amounted to about 40% of the total succinate degraded. Experiments designed to elucidate the mechanism of the excretion yielded the following observations. (i) The concentration of pyruvate in CP78 cells grown on the C4-dicarboxylic acids mentioned above was not significantly changed upon amino acid starvation. (ii) Guanosine 5'-diphosphate-3'-diphosphate exerted no effect on the activities of several enzymes thought to be involved in pyruvate-related metabolism. It is suggested firstly that the excretion was not due to some impairment in the biosynthetic pathway of a particular amino acid, but was due to the stringent control of central amphibolic metabolism, and secondly that no de novo protein synthesis was involved in the excretion.

Amino Acids↗

PubMed2002

Cystic forms of Borrelia burgdorferi sensu lato: induction, development, and the role of RpoS.

It has been demonstrated recently that cells of Borrelia burgdorferi sensu lato, the etiological agent of Lyme disease, transform from mobile spirochetes into nonmotile cystic forms in the presence of certain unfavourable conditions, and that cystic forms are able to reconvert to vegetative spirochetes in vitro and in vivo. The purpose of this study was to investigate the kinetics of conversion of borreliae to cysts in different stress conditions such as starvation media or the presence of different antibiotics. Using the same experimental conditions we also investigated the possible role in cyst formation of RpoS, an alternative sigma factor that controls a regulon in response to starvation and transition to stationary phase. We observed that beta-lactams penicillin G and ceftriaxone, the antibiotics of choice in Lyme borreliosis treatment, favoured the production of cysts when used with serum-depleted BSK medium. In contrast, we observed a low level of cyst formation in the presence of macrolides and tetracyclines. In order to elucidate the role of the rpoS gene in cyst formation we analyzed the reaction of the rpoS mutant strain in comparison with its wild-type in different conditions. Under the same stimuli, both the wild-type borrelia and the rpoS knock-out isogenic strain produced cystic forms with similar kinetics, thus excluding the participation of the gene in this phenomenon. Our findings suggest that cyst formation is mainly due to a physical-chemical rearrangement of the outer membrane of Borrelia burgdorferi sensu lato leading to membrane fusion and controlled by different regulation mechanisms.

Anti-Bacterial Agents↗

PubMed2006

Assessing the effects of Bt Maize on the predatory mite Neoseiulus cucumeris.

The investigation of Neoseiulus cucumeris in the context of the ecological risk assessment of insect resistant transgenic plants is of particular interest as this omnivorous predatory mite species is commercially available and considered important for biological control. In a multitrophic feeding experiment we assessed the impact of Bt maize on the performance of N. cucumeris when offered spider mites (Tetranychus urticae) reared on Bt (Bt11, Syngenta) or non-Bt maize (near isogenic line) and Bt or non-Bt maize pollen as a food source. Various parameters including mortality, development time, oviposition rate were measured. Spider mites were used as a prey for N. cucumeris, since these herbivores are known to contain similar levels of Cry1Ab toxin, when reared on Bt maize, as those found in the transgenic leaf material. In contrast, toxin levels in pollen of this transgenic cultivar are very low. No differences in any of the parameters were found when N. cucumeris was fed with spider mites reared on Bt and non-Bt maize. Pollen was shown to be a less suitable food source for this predator as compared to spider mites. Moreover, subtle effects on female N. cucumeris (9% longer development time and 17% reduced fecundity) were measured when fed with pollen originating from Bt maize as compared to non-Bt maize pollen. Our findings indicate that the predatory mite N. cucumeris is not sensitive to the Cry1Ab toxin as no effects could be detected when offered Bt-containing spider mites, and that the effects found when fed with Bt maize pollen can be assigned to differences in nutritional quality of Bt and non-Bt maize pollen. The significance of these findings is discussed with regard to the ecological relevance for risk assessment of transgenic plants.

Animals↗

PubMed1989

Determinants of the efficacy of tobramycin therapy against isogenic nonmucoid and mucoid derivatives of Pseudomonas aeruginosa PAO1 growing in peritoneal chambers in mice.

Mice which were supporting the growth of Pseudomonas aeruginosa in chambers implanted in their peritoneums were given two intramuscular injections of tobramycin (15 mg/kg of body weight each) at an interval of 8 h. Three hours later, chambers were removed and their contents were assessed for viable counts. Controls revealed that tobramycin levels in the chambers were 3.8 micrograms/ml 15 min after injection of 15 mg of tobramycin per kg and remained above the in vitro MICs (0.5 to 1 microgram/ml) for the tested strains for 8 h. It was demonstrated that tobramycin therapy was less effective with higher inocula and with longer delay before administration. Thus, in vivo, the concentration of bacteria in the chambers at the time of the first tobramycin injection had a profound effect on the bactericidal efficacy of tobramycin therapy. No such concentration dependence was observed in mock in vitro therapy experiments. A phage-selected mucoid derivative of P. aeruginosa PAO1 showed only a marginal increase in in vitro aminoglycoside susceptibility and no major alteration in in vivo susceptibility compared with its isogenic nonmucoid parent strain.

Animals↗