[Comparison of contrast behavior of gadobenate-dimeglumine and Gd-DTPA in intra-axial brain tumors. A double-blind randomized intraindividual cross-over study]. / Vergleich des Kontrastverhaltens von Gadobenat-Dimeglumine und Gd-DTPA bei intraaxialen Hirntumoren. Eine doppelblinde randomisierte intraindividuelle Cross-over-Studie.

The purposes of the study was to assess intra-axial brain tumors by a blinded comparison of gadobenat-dimeglumine and Gd-DTPA. 27 patients with known cerebral gliomas or metastases were included into an intra-individual randomized double-blinded cross-over study. The protocol included T1 SE, T2 FSE and after contrast a series of five T1 SE sequences followed by T1 SE with MT, T1 SE, and 3D GRE sequences. Imaging data acquired at two centers were assessed on-site by the investigators and off-site by two experienced readers using quantitative and qualitative criteria. For a quantitative analysis tumor contrast and contrast-to-noise ratios were determined out of ROI in tumor, unaffected white matter, a region outside the head, and an external reference tube. For the qualitative assessment on- and off-site readers were asked to compare both MR scans for lesion contrast, lesion delineation and information upon the internal morphology and structure. In the quantitative analysis lesions examined with gadobenat-dimeglumine present a maximal 26% increase of the lesion contrast. In both, the on-site, as well as the off-site assessment the intensity of enhancement and the lesion contrast were found to be significantly better with gadobenat-dimeglumine enhanced MRI. There was a trend towards gadobenat-dimeglumine for the delineation of the lesion from the surrounding tissue and the internal lesion morphology. Based on our observations gadobenat-dimeglumine proved to be a safe and valuable contrast media for the assessment of CNS neoplasms. Compared with Gd-DTPA it provides a more intense contrast enhancement and a better tumor contrast which might be of importance for the further management of these patients.

Occurrence of S and F1C/S-related fimbrial determinants and their expression in Escherichia coli strains isolated from extraintestinal infections.

The presence of S and F1C/S-related fimbrial determinants was determined in 462 E. coli strains obtained from different extraintestinal infections and in 162 control isolates of E. coli by using two different DNA probes: an oligonucleotide probe consisting of three oligonucleotides that bind specifically to the S adhesin gene and a polynucleotide probe which is not able to distinguish between S, F1C, and S-related sequences. The expression of S and F1C phenotypes was tested by dot enzyme immunoassay with the corresponding monoclonal antibodies. S fimbriae genotypes were observed more frequently in septic (25%) and urinary (12%) isolates of E. coli than in faecal and water isolates (1%) and often occurred together with O2, O6, O18 and O83 antigens. F1C/S-related fimbrial DNA was detected with a higher frequency in UTI isolates (26%) than in septic (16%) and faecal (10%) isolates and was most frequently associated with O4, O6, and O75 serotypes. Since the production of S and F1C fimbriae was comparatively rare in all clinical and control isolates of E. coli, DNA hybridization assays which allow the sensitive and specific detection of fimbrial determinants even in the absence of their expression are preferable to phenotypic assays.

Inter-laboratory ring trial of in vitro DNA repair tests using rat hepatocytes: further testing and conclusive remarks.

The results of the extension of a collaborative study for the detection of chemical-induced DNA damage in rat hepatocytes in vitro are presented in this report. Three coded compounds, i.e. 1,4-butanediol dimethanesulphonate, hydrazine sulphate and sodium dichromate, were tested for DNA repair synthesis by seven different laboratories, either using autoradiographic procedures or the liquid scintillation counting technique. Inter-laboratory standardization was intentionally not requested in order to investigate the validity of each study design under routine conditions. 1,4-Butanediol dimethanesulphonate was clearly positive in most laboratories; sodium dichromate was generally positive, while the results on hydrazine sulphate were contradictory.

Activity of 1,2-dimethylhydrazine in the mouse bone marrow micronucleus assay using a triple- and a single-dosing protocol.

In the present study the ability of 1,2-dimethylhydrazine (DMH) to induce micronuclei in mouse bone marrow erythrocytes was investigated using 2 different dosing regimens. DMH caused an increase in micronuclei in both male and female mice following single administration and sampling after 24 h. The effect was more pronounced in female than in male animals. Triple administration of DMH at concentrations corresponding to 80, 40 and 20% of the median lethal dose (MLD) did not increase the incidence of micronuclei in either sex. Small increases in micronucleus incidence were observed after triple dosing at 100% of the MLD value. These results suggest that a future micronucleus protocol should include animals of both sexes and single and repeated administration of the test substance.

High-dose-level effects in mutagenicity assays utilizing mammalian cells in culture.

We report here results obtained using sodium chloride and potassium chloride as model compounds to investigate the effects of high dose levels and osmolarity-mediated artefacts in mutagenicity assays using cultured mammalian cells. Three assay systems were used with different genetic end-points: (i) mutation to 6-thioguanine resistance in Chinese hamster V79 cells; (ii) induction of chromosome aberrations in Chinese hamster ovary cells; and (iii) induction of unscheduled DNA synthesis in HeLa S3 cells. In V79 cells we observed sporadic increases in mutation frequency after treatment with sodium chloride. Potassium chloride increased the mutation frequency in a narrow interval of dose levels. Chromosome aberrations were induced by both compounds at the highest concentrations tested, confirming previously published data; the effects of potassium chloride were more marked. The chromosome aberrations observed included both deletions and exchange figures. Neither compound induced UDS in our experiments. We performed the Ames test as a check for mutagenic contaminants and both compounds gave entirely negative results. Although the osmolarities of sodium chloride and potassium chloride solutions were similar, the effects of potassium chloride were always greater at equivalent concentrations; the nature of the solute, and not only the observed osmolarity, appears to influence the results obtained. Similarly, we have observed that dimethylsulphoxide causes a marked increase in the osmolarity of the culture medium without any obvious induction of chromosome aberrations. Although the presence of S9 had little effect on the osmolarity of the medium, differences in response were observed after treatments with or without S9. For the two model compounds it appears that an osmotic mechanism alone does not provide a sufficient explanation of the findings.

Application of in-vitro models: development of resistance.

The development of chromosomal beta-lactam resistance of Escherichia coli, Enterobacter cloacae and Citrobacter freundii was observed by following the bacterial kill-kinetics in an in-vitro model simulating human serum antibiotic concentrations. From sensitive Escherichia coli cells mutants arose resistant to aminopenicillins, and to first and second generation cephalosporins, whereas with the Ent. cloacae and Citro. freundii mutants were also resistant to cefotaxime. Resistant mutants from all three species could also be selected on antibiotic-containing agar plates. With E. coli they occurred in two steps, the first mutation being stable but the second mutation reverting spontaneously. In Ent. cloacae, and apparently also in Citro. freundii, the mutation changes the cephalosporinase production from an inducible to a constitutive one. The different mutation rates, and the rate was extremely high for some Ent. cloacae strains, were correlated with a corresponding reduction of viable cell count and with the time of re-growth observed in the model.

The activity of cefotiam on beta-lactamase-producing bacteria in an in-vitro model.

The activity of cefotiam was tested in an in-vitro model simulating human serum pharmacokinetics. Bacterial strains used for inoculation either produced a penicillinase or a cephalosporinase. The rate of hydrolysis and the MICs of cefotiam were determined in comparison with those of ampicillin and cephalothin. The influence of these beta-lactamases on the killing kinetics and the degradation of cefotiam in the in-vitro model were then measured. Although all beta-lactamases hydrolyzed cefotiam, only the chromosomal cephalosporinases, especially those from Enterobacter and Klebsiella, reduced the elimination of the bacteria by degradation of the drug. A rough correlation between the hydrolytic activity and MIC could be demonstrated for cefotiam but not for ampicillin, while a correlation between killing ability and MIC only existed for strains with cefotiam MICs higher than 16 mg/l.

Transfer of the chromosomal bla gene from Enterobacter cloacae to Escherichia coli by RP4::mini-Mu.

The resistance gene for beta-lactamase-stable cephalosporins from Enterobacter cloacae was transferred to Escherichia coli by the aid of RP4::mini-Mu. The R-prime plasmids generated carried 60 to 80 kilobases (kb) of E. cloacae DNA and coded for the chromosomal E. cloacae beta-lactamase. The gene was fully expressed in the recipient. Restriction endonuclease EcoRI fragments of the R-prime plasmid pBP100 were cloned into the vector pBP328, yielding the plasmid pBP102 with a size of 14 kb. A restriction map of this plasmid was constructed. By digesting pBP102 into seven PstI fragments, ligating the fragments, and looking for the smallest plasmid generated, pBP103 was isolated. It consisted of three PstI fragments, two of them (together 4.2 kb) necessary for resistance. During the experiment (performed in a recA+ background) the largest PstI fragment had undergone a substitution of a 0.3-kb segment of pBP102 by a 0.7-kb segment in pBP103 (as deduced by heteroduplex analysis). The bla gene of resistant E. cloacae strains was dominant over the gene of susceptible organisms.

A microbiological evaluation of apalcillin.

The in vitro activity of apalcillin was tested against 350 clinical isolates of Escherichia coli, Enterobacter, Klebsiella, Proteus, Pseudomonas aeruginosa and Streptococcus faecalis. Using a minimal inhibitory concentration of 16 mg/l as the breakpoint, only 19.7% of the strains were resistant to apalcillin. A regression analysis demonstrated that it is possible to test bacteria for sensitivity with a 20 micrograms apalcillin disc. The results on Mueller-Hinton agar are very similar to those on Iso-Sensitest medium. Like other ureido penicillins, apalcillin is sensitive to most beta-lactamases; it is effective against ampicillin-resistant strains since it penetrates the outer membrane of gram-negative bacteria well and is highly effective against target proteins. Strains producing high amounts of beta-lactamases do become resistant to apalcillin.

Chromosomal beta-lactamases of Enterobacter cloacae are responsible for resistance to third-generation cephalosporins.

About 70% of all Enterobacter cloacae strains tested possessed one of two species-specific beta-lactamases. These enzymes, E. cloacae beta-lactamase A and E. cloacae beta-lactamase B, with isoelectric points of 8.8 and 7.8, respectively, had the same pH and temperature optima. Both showed similar enzyme kinetics and were inhibited by cloxacillin but not by p-chloromercuribenzoate. E. cloacae beta-lactamase B appeared to be identical with the enzyme of E. cloacae P99. By a mutation in a regulatory gene, inducible enzyme production could be converted into constitutive expression. In E. cloacae, both enzymes did not hydrolyze third-generation cephalosporins, but they were solely responsible for resistance toward these drugs. This was demonstrated by the characterization of Escherichia coli strains expressing an identical resistance pattern after transfer of the corresponding Enterobacter gene.