Biomedical subjects
S Kreps
Publications and source records attributed to S Kreps.
Detection of choroidal calcium by computed tomography scan quantitative computerized tomography: a clinically useful diagnostic tool.
OBJECTIVE: Quantitative computerized tomography (QCT), a scanning method routinely used to classify tissues based on their radio density, was used to detect choroidal calcification. DESIGN: Case reports. PARTICIPANTS: Two patients with known or suspected choroidal calcium-choroidal osteoma (CO) and pseudoxanthoma elasticum (PXE) and five normal control subjects were assessed. INTERVENTION: The CT scan of choroid, B-scan ultrasound, fluorescein angiography. MAIN OUTCOME MEASURES: The QCT scan used to detect the presence of calcium based on a readout greater than 90. RESULTS: Calcium was detected bilaterally, as predicted, in PXE, and in both eyes of CO, although only one eye had a clinically noted lesion. No control eye gave a scale readout consistent with calcium. No findings suggestive of calcium were noted with B-scan ultrasound or fluorescein angiography in PXE or CO. CONCLUSION: The QCT can detect calcium in the choroid when B-scan ultrasonography and CT scan fine sectioning fail to identify calcium despite high clinical suspicion.
Poisson-like fluctuation patterns of revertants of leucine auxotrophy (leu-500) in Salmonella typhimurium caused by delay in mutant cell division.
Leu+ mutants from Salmonella typhimurium leu-500 strain MA412 arise at high frequencies and mutant colonies appear over a broad range of time on selective plates. This observation suggested that these Leu+ mutants might be induced or "directed."= If such a mechanism was responsible, mutants should originate on selective plates rather than in the preceding culture in nonselective conditions and should give rise to Poisson-like fluctuation curves upon plating of sister cultures on selective medium. Poisson-like distribution profiles were indeed observed for Leu+ mutants of S. typhimurium MA412. However, an explanation for the observed Poisson-like fluctuation patterns without a need for selection-induced mutations was found. Microscopical analysis and cell mass/viable count measurements showed that the size of Leu+ mutant cells was often much larger than those of nonmutants. This size difference was a stable characteristic of a large proportion of Leu+ mutants, was observed both in stationary and growing culture and did not measurably affect the division rates of the cells in nutrient broth. As the transition from normal-sized nonmutant to oversized mutant cells during the nonselective culture phase of the fluctuation experiment may have been accompanied by a period with no or few completed cell division cycles, the number of mutant offspring may have been smaller than that of sibling nonmutants. Such underrepresentation of mutants in the final culture is expected to give rise to Poisson-like fluctuation patterns without invoking "directed" mutations.
Construction and characterization of heavy metal-resistant haloaromatic-degrading Alcaligenes eutrophus strains.
Alcaligenes eutrophus strains exhibiting both plasmid-borne heavy metal resistance and haloaromatic-degrading functions were obtained by intraspecific conjugation. The strains which we constructed expressed catabolic and resistance markers together. Degradation of various polychlorinated biphenyl isomers and 2,4-D (2,4-dichlorophenoxyacetic acid) was observed in the presence of 1 mM nickel or 2 mM zinc, provided that the metal resistance determinant was present in the catabolizing strain. Such strains may be useful for decontamination of sites that are polluted with both organic compounds and heavy metals.
Identification of a catabolic transposon, Tn4371, carrying biphenyl and 4-chlorobiphenyl degradation genes in Alcaligenes eutrophus A5.
Alcaligenes eutrophus A5 catabolizes biphenyl to CO2 via benzoate and 4-chlorobiphenyl to 4-chlorobenzoate. In curing and conjugation experiments, the A5 endogenous 51-kb IncP1 plasmid pSS50 was found to be dispensable for biphenyl and 4-chlorobiphenyl catabolism. Transfer of the biphenyl- and 4-chlorobiphenyl-degrading phenotype by means of pSS50 was observed at a frequency of 10(-5) per transferred plasmid in matings of A5 with other A. eutrophus strains. Transconjugants harbor enlarged pSS50 derivatives which contain additional genetic information governing the oxidation of biphenyl and 4-chlorobiphenyl to benzoate and 4-chlorobenzoate and originating from the chromosome of strain A5. The following observations indicate that the catabolic genes reside on a 59-kb large transposon (Tn4371) for which a restriction map is presented. (i) Tn4371 transposes between different replicons and at different locations of the same replicon. (ii) Transposition was observed in a Rec- strain of A. eutrophus. (iii) Tn4371 transposes as a single, contiguous piece of DNA. Although an RP4::Tn4371 plasmid was stably maintained in different hosts, the plasmid conferred growth on biphenyl only when present in strains of A. eutrophus and in an Acinetobacter sp. strain.
Synergistic toxicity of IFN-gamma-producing Escherichia coli K12 cells.
Genetically modified microorganisms (GMMs) are frequently used as producers of mammalian immunomodulatory proteins, e.g. interferons and interleukins. Here we have examined the question of whether such GMMs interact in a way different from that of their non-modified parent micro-organisms with mammalian antimicrobial defence systems. As a typical GMM host micro-organism we used Escherichia coli K12, and as a typical immunomodulatory protein produced by a GMM we used mouse interferon-gamma (MuIFN-gamma). Two experimental systems are described in which synergistic "toxic" biological effects are induced by a combined treatment with E. coli and MuIFN-gamma but not, or less so, by the parental strain and the recombinant protein separately. First, it is shown that the IFN-gamma-producing GMM, or mixtures of E. coli cells and IFN-gamma, are cytolytic for mouse embryo fibroblastoid cells (MEF), whereas no cell killing occurs in MEF cultures treated with control E. coli cells or in those treated with bacteria-free recombinant IFN-gamma. Second, it is demonstrated that intraperitoneal injection in mice of high but not low numbers of control E. coli K12 cells induces a shock-like mortality, whereas co-injection with IFN-gamma induces killing at low numbers. IFN-gamma-producing E. coli cells cause a mortality rate that does not differ from that of control E. coli cells, probably because in these experimental conditions the level of recombinant MuIFN-gamma per cell is insufficiently high. Taken together, these data indicate that synergistic toxic effects induced by bacteria and their recombinant products can occur and may in certain situations enhance the intrinsic toxic capacity of the GMM. Synergistic toxic effects may thus be of relevance for identifying the safety level that should be employed when working with GMMs.
Rapid method for purification of soil DNA for hybridization and PCR analysis.
Monitoring of microbial DNA in soils by dot blot hybridization and PCR analysis is a useful technique for gaining insight into the survival and impact of genetically modified micro-organisms released in the environment. Most methods of DNA isolation from soils require a large number of purification steps rendering them unsuitable for quantitative analysis of multiple samples. Here we describe a very rapid method for the isolation and purification of multiple samples of soil DNA that can be used directly for dot blot hybridization and PCR analysis. Soil DNA extracts are prepared by lysozyme/SDS treatment at pH 9.0 and purified by ammonium acetate precipitation and Sephadex G50 gel filtration. In a practical application of this method, sandy soil samples were seeded with Alcaligenes eutrophus cells and exposed to high temperature (42 degrees C) or desiccation. As a result, the number of culturable A. eutrophus cells which could be recovered from the soil samples quickly declined. However, the concentration of a marker gene encoding resistance to cadmium, cobalt and zinc (czc) remained unaltered.
Uncommon CT patterns of subdural hematomas managed nonsurgically.
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[Medical assistant's role in the prevention and early detection of incidents caused by cytostatic agents].
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Computerized tomography correlated with CSF protein concentrations.
The authors present a case of hydrocephalus complicated by ventriculitis in which it was possible to correlate the numerical printout of sequential computerized tomograms (CT-Scans) with cerebrospinal fluid protein concentrations obtained by direct ventricular puncture. Different protein levels were unambiguously associated with changes in the absorption numbers on the scan but they did not bear a simple linear relationship to one another. The value of the numerical printout in diagnosis and follow-up is discussed.