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K Shannon

Publications and source records attributed to K Shannon.

At least 55 records · Page 3Linked to original sources
PubMed1995

DNA sequence differences of ampD mutants of Citrobacter freundii.

Three groups of mutants with increased levels of beta-lactamase synthesis were selected from Citrobacter freundii 382010 by beta-lactam antibiotics at concentrations just above the MIC. Uninduced cultures of the hyperinducible group had 3- to 5-fold more beta-lactamase activity than the parent strain, with one mutant (termed type b) expressing 19 times the activity of the parent strain; the partially derepressed group had a relative 55-fold increase, while fully derepressed strains exhibited a 460-fold increase. Upon induction by growth in the presence of cefoxitin (32 micrograms/ml) for 2 h, the hyperinducible and derepressed groups had similar relative beta-lactamase activities of 650 and 725, respectively. Induction of beta-lactamase activity from partially derepressed mutants resulted in a relative activity of only 240. The ampD gene including its promoter region was amplified from the parent strain and the mutant strains by PCR. The sequence of ampD from the parent strain showed only three nucleotide changes from a previously published sequence, none of which resulted in a change to the deduced amino acid sequence. Hyperinducible mutant strains of type a had an amino acid change of either a tryptophan in codon 95 to an arginine (Trp-95-->Arg) (three mutants) or Ala-158-->Asp (one mutant). The hyperinducible type b strain had the change Tyr-102-->Asp. The derepressed strains had the following changes: Val-33-->Gly (one mutant), Asp-164-->Glu (one mutant), and Trp-95-->termination codon (two mutants). We infer that the amino acid changes in the hyperinducible mutants result in altered AmpD activity, whereas, in contrast, they lead to an inactive protein in derepressed mutants. No nucleotide differences were found in the ampD gene from partially derepressed strains.

Anti-Bacterial Agents↗
PubMed1995

Recombinant human erythropoietin in neonatal anemia.

Recombinant human erythropoietin (r-HuEPO) is a new therapeutic modality for the treatment of neonatal anemia. The results of three large controlled trials were published within the past year. This article reviews the physiologic rationale underlying the use of r-HuEPO in preterm infants, addresses how the design of clinical trials affects outcomes and conclusions, and discusses the recent trials in this context. The article concludes with a summary of questions that require further investigation.

Anemia, Neonatal↗
PubMed1994

Effect of hyperproduction of TEM-1 beta-lactamase on in vitro susceptibility of Escherichia coli to beta-lactam antibiotics.

The susceptibility of 173 TEM-1-producing isolates of Escherichia coli was assessed by determination of MICs by the agar dilution method. MICs of amoxicillin, mezlocillin, cephaloridine, and, to a smaller extent, amoxicillin-clavulanic acid (but not cephalexin, cefuroxime, cefotaxime, ceftazidime, or imipenem) were higher for isolates that produced large amounts of beta-lactamase than for isolates that produced smaller amounts. The effect of fixed concentrations of clavulanic acid on resistance to amoxicillin was assessed for 34 selected TEM-1-producing isolates. Low concentrations of the inhibitor (0.5 to 1 microgram/ml) reduced the amoxicillin MICs substantially for almost all the isolates, although the reductions were not sufficient to render any of the isolates amoxicillin susceptible. Higher concentrations of clavulanic acid had progressively greater effects on amoxicillin MICs, but even at 8 micrograms/ml some of the isolates with high beta-lactamase activities remained resistant or only moderately susceptible to amoxicillin. All the isolates were inhibited by clavulanic acid (in the absence of amoxicillin) at concentrations of 16 to 32 micrograms/ml. TEM-1 beta-lactamase activity was inhibited in vitro by clavulanic acid, but not totally, with approximately 2% of the initial activity remaining at 2 micrograms/ml and 0.4% remaining at 8 micrograms/ml. These findings suggest that the amount of beta-lactamase activity is a major determinant of the degree of resistance to several beta-lactam antibiotics and can make the difference between susceptibility and resistance to some compounds, notably the combination of amoxicillin with clavulanic acid.

Amoxicillin↗
PubMed1994

Lymphoid blast crisis of B-lineage phenotype with monosomy 7 in a patient with juvenile chronic myelogenous leukemia (JCML).

We studied a patient with juvenile chronic myelogenous leukemia (JCML) whose terminal course was characterized by transformation to acute lymphoblastic leukemia. Karyotypic studies identified monosomy 7 in leukemic myelomonocytic marrow cells during the chronic phase and in the lymphoblasts during the transformation phase. Our ability to sustain the transformed lymphoblasts in culture allowed us to characterize them further. CD19, HLA-DR, and CD10 were present, consistent with a pre-B acute lymphoblastic leukemia phenotype. CD14 (My-4) and CD13 (My-7) were negative. Rearrangement of immunoglobulin heavy- and light-chain genes identified monoclonal populations of cells of the B lineage. This case provides further evidence that JCML is a clonal disease of pluripotent stem-cell origin.

Blast Crisis↗
PubMed1993

Do terminal deletions of 11q23 exist? Identification of undetected translocations with fluorescence in situ hybridization.

Fluorescence in situ hybridization (FISH) was performed on bone marrow or peripheral blood cells thought to contain a del(11)(q23q25) from four patients who had acute leukemia or myelodysplasia. Cells from all patients were shown to contain translocations that involved chromosome 6 in three of them. Our data suggest that a large proportion of presumptive del(11)(q23) or del(11)(q23q25) chromosomes may represent previously unidentified translocations that can be detected by FISH.

Acute Disease↗
PubMed1993

Importance of beta-lactamase induction.

Induction of an enzyme is a temporary phenomenon in which the rate of enzyme synthesis is greatly increased in response to the presence of an inducer in the environment. Induction of beta-lactamase synthesis is important for the resistance of staphylococci to penicillins since the drug both induces synthesis of the enzyme and is hydrolysed by it. Similarly, some compounds both strongly induce and are hydrolysed by the chromosomally-determined beta-lactamases of gram-negative bacilli (e.g. amoxicillin and cefoxitin for Enterobacter cloacae). Other compounds (e.g. piperacillin and cefotaxime) although labile are poor inducers, so that in the case of these drugs the phenomenon of induction is not important but the presence of the enzyme is, since resistant mutants with genetically derepressed synthesis of the enzyme can emerge. Induction can also be important when a strong inducer is present with a poor inducer and antagonises the activity of the latter.

Anti-Bacterial Agents↗
PubMed1992

Prevalence of resistance to beta-lactam antibiotics in Escherichia coli isolated from blood from 1969-1991.

MICs of beta-lactam antibiotics were determined for blood culture isolates of Escherichia coli from patients in St. Thomas' Hospital, London between 1969 and 1991. There was correlation between MICs of carbenicillin and those of amoxycillin (Kendall's coefficient of rank correlation, tau = 0.67), mezlocillin (tau = 0.73), cephaloridine (tau = 0.64) and amoxycillin/clavulanic acid (tau = 0.72), but less correlation between MICs of carbenicillin and cefuroxime (tau = 0.31). During the two decades, the geometric mean MICs increased for carbenicillin (6.6-fold increase in mean MIC), mezlocillin (3.4-fold increase in mean MIC), cephaloridine (two-fold increase in mean MIC) and, to a smaller extent, amoxycillin/clavulanic acid (1.2-fold increase in mean MIC), but not for cefuroxime. These changes were the result of increases in the proportion of isolates that were resistant to carbenicillin and not of changes in the phenotype of carbenicillin-resistant isolates.

Amoxicillin↗
PubMed1991

Mutations of the ras proto-oncogenes in childhood monosomy 7.

ras gene mutations are the most frequent molecular changes found in the preleukemic syndromes of adults and may play a role in initiating these diseases and in their progression to acute leukemia. However, little is known about the incidence or importance of these genetic mutations in childhood myeloproliferative states (MPS). The bone marrow (BM) monosomy 7 syndrome accounts for a large percentage of childhood MPS. Although the duration of the MPS is quite variable, children with monosomy 7 eventually develop acute myeloid leukemia (AML). We investigated 20 children (13 with MPS, 7 with AML) with BM monosomy 7 or 7q- for the presence of ras gene mutations using the polymerase chain reaction and hybridization with mutation-specific oligonucleotides. Mutations of N-ras and K-ras were detected in three children. Two patients carrying a ras mutation were in the myeloproliferative phase, and one had acute leukemia. All three patients with ras mutations either died of their disease or relapsed after BM transplantation as compared with 8 of 17 without ras mutations. However, this difference is not statistically significant (P = .14, not significant). We conclude that ras mutations are observed in childhood monosomy 7, though less frequently than in adult MDS, and may play a limited role in the progression of this disease to acute leukemia. More patients are needed to address the prognostic role of ras mutations in this rare disease.

Bone Marrow↗
PubMed1991

Experience with 998 cutaneous melanomas of the head and neck over 30 years.

Between 1960 and 1990, a total of 998 patients were treated at the Sydney Melanoma Unit for cutaneous melanoma of the head and neck. There were 595 male and 403 female patients, with a median age of 53 years. The most common primary lesion site was the face (47%), followed by the neck (29%), scalp (14%), and ear (10%). Histologic types were as follows: superficial spreading 30%, nodular melanoma 28%, lentigo maligna melanoma 16%, and other 26%. All patients underwent surgical treatment. Primary closure of wounds was achieved in 52% of patients, and excision margins were 2 cm or less in 45%. A total of 152 patients had therapeutic neck dissections, and 234 had elective neck dissections. The overall local recurrence rate was 13%, and this was significantly influenced by increasing tumor thickness and Clark level. The recurrence rate in the neck after neck dissection was 24%, and the rate of parotid recurrences was 14%. Melanoma-specific survival was 77% at 5 years and 66% at 10 years for the entire group. By univariate analysis, survival varied significantly with age, tumor thickness, ulceration, anatomic sub-site, histologically positive nodes, and the presence of distant metastases. A diagnosis of lentigo maligna melanoma and elective lymph node dissection both appeared to improve survival. With multivariate analysis, all of these factors remained significant prognostic factors except elective node dissection, which lost its beneficial influence.

Female↗
PubMed1990

Hyperproduction of TEM-1 beta-lactamase in clinical isolates of Escherichia coli serotype O15.

During an outbreak of infection with ampicillin-resistant, TEM-1 beta-lactamase-producing Escherichia coli serotype O15, some strains were noted to differ from the majority in that they showed reduced susceptibility to amoxycillin/clavulanic acid (Augmentin), ureidopenicillins and first generation cephalosporins and produced increased amounts of beta-lactamase. The plasmid from one such isolate was compared with that from an isolate that produced normal amounts of beta-lactamase. Restriction analysis with EcoRI revealed extra fragments in the plasmid from the beta-lactamase hyperproducer and use of DNA-DNA hybridisation with a biotinylated TEM-1 probe showed genetic rearrangement in the beta-lactamase hyperproducer so that the TEM gene appeared to be present in larger amounts and was located on a smaller fragment than for the plasmid from the strain that produced normal amounts of beta-lactamase.

DNA, Bacterial↗
PubMed1990

Alcohol protects the diaphragm during dietary restriction.

We recently reported that alcoholic rat diaphragm develops greater contractile force than diaphragm of pair-fed control animals. The present experiment examines whether alcohol or dietary restriction is the more likely cause of this surprising finding. We conditioned 10 rats using a liquid diet containing ethanol as 36% of calories. Ten pair-fed control animals received an equal amount of isocaloric, ethanol-free liquid diet. Ten ad libitum control animals had unrestricted access to lab chow and water. Rats were killed after 30 weeks. Left costal diaphragm strips were studied in vitro at optimal length using direct stimulation at supramaximal voltage. Isometric force was measured and divided by muscle cross-section to compute stress. Maximal tetanic stresses developed by muscle from pair-fed controls were systematically less than alcoholic and ad libitum control values (p less than 0.0001); this did not depend on temperature (25 degrees vs. 37 degrees; p greater than 0.50). Pair-feeding increased twitch half-relaxation times (p less than 0.03) and shifted the tetanic stress-stimulation frequency relationship leftward by 10 Hz (p less than 0.01). Diaphragm of pair-fed rats continued to generate lower stresses during the fatigue caused by repeated contractions (p less than 0.01). We conclude that dietary restriction associated with pair-feeding compromises diaphragm performance in rats. Chronic alcohol consumption prevents or reverses these changes, since diaphragm function of alcoholic and ad libitum control animals was not different.

Alcoholism↗
PubMed1990

Relapsing post-hepatitis aplastic anemia. Immunosuppressive therapy.

A 20-month-old Hispanic male developed severe aplastic anemia after an episode of non-A, non-B hepatitis. Prompt and complete recovery of all hematopoietic cell lines occurred after treatment with antithymocyte globulin (ATG) and high-dose corticosteroids. Severe aplasia recurred two months later coincident with a mild upper respiratory infection. A second course of immunosuppressive therapy was followed by complete, sustained improvement. The authors' experience provides clinical evidence indicating that immunologic mechanisms are important in the treatment of severe post-hepatitis aplastic anemia. Children in whom aplastic anemia recurs after immunosuppressive treatment may respond to a second course of therapy.

Adrenal Cortex Hormones↗
PubMed1989

Effect of nifedipine on the contractile function of the rat diaphragm in vitro.

The isometric contractile response of the directly-stimulated rat diaphragm was studied before and following addition of the calcium channel blocker, nifedipine. Nifedipine (10 micrograms/ml and 30 micrograms/ml bath concentrations) significantly increased isometric force output during twitch and unfused tetanic stimulation. Force potentiation during unfused tetanic stimulation was equivalent during either high or low voltage stimulation. Nifedipine had no effect on the time to peak force, half relaxation time, or relaxation time during twitch stimulation; thus, both activation and relaxation rates were increased. The force potentiating actions of nifedipine persisted in a calcium-free bathing solution and were enhanced by d-tubocurarine. In contrast to the force enhancing effects found with twitch and unfused tetanic stimulation, nifedipine caused a small but significant reduction in isometric force during maximal fused tetanic stimulation. It is concluded that the force potentiating effects of nifedipine on rat diaphragm are not due to fiber recruitment, enhancement of neuromuscular excitation, or altered inward trans-sarcolemmal calcium flux, but may result from a direct effect of the drug on the rate of activation of the contractile apparatus.

Animals↗