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Biomedical subjects

D C Hooper

Publications and source records attributed to D C Hooper.

At least 145 records · Page 8Linked to original sources
PubMed1986

Genetic and biochemical characterization of norfloxacin resistance in Escherichia coli.

In Escherichia coli the frequency of spontaneous single-step mutation to high levels of resistance to the newer 4-quinolone agent norfloxacin was confirmed to be over 300-fold lower than that to the older agent nalidixic acid. Serial passage on incremental concentrations of drug was necessary to produce mutants highly resistant to norfloxacin. Genetic analysis of one such highly resistant strain identified two mutations conferring drug resistance. One mutation, nfxA, mapped around 48 min on the E. coli genetic map and was shown to be an allele of gyrA by studies demonstrating an increased drug resistance of DNA gyrase reconstituted with the gyrase A subunit isolated from the mutant strain. These findings also identified the DNA gyrase A subunit as a target of norfloxacin. The second mutation, nfxB, mapped between 20 and 22 min was associated with additional resistances to tetracycline, chloramphenicol, and cefoxitin and with decreases in outer membrane porin protein OmpF. The nfxA and nfxB mutations together accounted for most, but not all, of the norfloxacin resistance phenotype of this strain.

Bacterial Outer Membrane Proteins↗
PubMed1985

Knotting of DNA molecules isolated from deletion mutants of intact bacteriophage P4.

DNA molecules isolated from tailless phage particles (capsids) of bacteriophage P4 virl del10 are known to be knotted. We have found by electron microscopy that 80% of DNA molecules isolated from intact phage particles of P4 virl del10 also contained knots. This observation indicates that the predominant form of P4 virl del10 DNA within the intact phage particle is either knotted or in a configuration that permits knotting upon isolation. In comparison to P4 virl del10 (deleted 1000 basepairs), DNA molecules isolated from intact P4 virl del2 (deleted 650 basepairs) and P4 virl (non-deleted) contained 50% and 15% knots respectively, showing an association of decreased size of deletion of DNA with a decreased fraction of knotted genomes.

Chromosome Deletion↗
PubMed1985

In vitro activation of bone marrow-derived T-and non-T-cell subsets by alpha-fetoprotein.

Alpha-Fetoprotein (AFP) is a major serum glycoprotein during embryonic and early postnatal life. A number of diverse biologic functions have been attributed to AFP, including osmotic and carrier function and immunosuppressive activity. In this study we demonstrate that AFP selectively stimulates in vitro proliferation of two distinct subsets of adult murine bone marrow cells. One population of AFP-reactive bone marrow cells expresses surface receptors for soybean agglutinin (SBA) lectin. SBA+ bone marrow cells are resistant to cytotoxic pretreatment with T-cell-specific antisera and are not retained on Ig-anti-Ig affinity columns. The absence of conventional T- and B-cell markers, coupled with the presence of SBA receptors, suggests that AFP-activated non-T bone marrow cells may belong to an immature set of B lymphocytes. A second population of AFP-responsive bone marrow cells expresses the Thy-1+ Lyt 1+2- phenotype characteristic of conventional mature adult T helper cells. The potential physiological relevance of the mitogenic effects of AFP on bone marrow cells with respect to immunoregulatory processes in the fetal/newborn environments is discussed.

Animals↗
PubMed1985

Temperature effects on evoked potentials of hippocampal slices from euthermic chipmunks, hamsters and rats.

1. Neural activity was recorded in hippocampal slices from euthermic chipmunks, hamsters and rats. 2. While recording the evoked potentials, the temperature of the Ringer's solution bathing the slice was varied by controlling the temperature of an outer chamber jacketing the recording chamber. 3. The temperature just below that at which a population spike could be evoked, Tt, was 10.4 +/- 0.3 degrees C (mean +/- SEM) for chipmunk slices, 14.1 +/- 0.4 degrees C for rat slices and 14.8 +/- 0.4 degrees C for hamster slices. Tt was significantly lower in the chipmunk slices (P<0.01) than in the rat and hamster slices. 4. Data were interpreted as consistent with the hypothesis that chipmunk hippocampal neurons are intrinsically cold resistant.

Animals↗
PubMed1985

Central nervous system infection in the compromised host.

The possible causes of central nervous system infection in the compromised host are many. Careful consideration of the underlying defects in host defenses, the epidemiology of infection, and the clinical findings, however, can narrow these possibilities and focus diagnostic testing. Aggressive attempts at early diagnosis and therapy offer the potential for meaningful survival.

Antibody Formation↗
PubMed1984

Elimination of plasmid pMG110 from Escherichia coli by novobiocin and other inhibitors of DNA gyrase.

The ability of novobiocin to eliminate (cure) the wild-type plasmid pMG110 from Escherichia coli has been compared with that of other inhibitors of the gyrase B subunit and of the gyrase A subunit. Novobiocin eliminated pMG110 , producing over 99% plasmid loss at concentrations two- to eightfold below the MIC for bacterial growth. Structurally related compounds ( clorobiocin , coumermycin A1, isobutyryl novenamine , and decarbamyl novobiocin) varied in their ability to eliminate pMG110 . Higher concentrations of drugs were required to eliminate pMG110 from a gyrB( Cour ) strain, implicating DNA gyrase in the curing phenomenon. For these drugs, the ratio of the concentration effecting maximal plasmid elimination to the MIC varied from 0.16 to 1.1, indicating that curing cannot be explained simply by inhibition of a pool of DNA gyrase equally available for replication of the bacterial chromosome and the plasmid DNA molecule. Inhibitors of the gyrase A subunit, nalidixic acid and oxolinic acid, eliminated pMG110 only to variable low levels. The differences in the ability of the gyrase A and B subunit antagonists to eliminate plasmids are discussed.

Escherichia coli↗
PubMed1984

Pasteurella multocida infections. Report of 34 cases and review of the literature.

Pasteurella multocida, a small, gram-negative coccobacillus , is part of the normal oral flora of many animals, including the dog and cat. P. multocida is the etiologic agent in a variety of infectious disease syndromes. We have reported 34 cases of infection caused by P. multocida and have reviewed the English literature. P. multocida infections may be divided into three broad groups: 1. Infections resulting from animal bites and scratches : The most common infections caused by P. multocida are local wound infections following animal bites or scratches . Cats are the source of infection in 60 to 80% of cases and dogs in the great majority of the remainder. Local infections are characterized by the rapid appearance of erythema, warmth, tenderness, and frequently purulent drainage. The most common local complications are abscess formation and tenosynovitis. Serious local complications include septic arthritis proximal to bites or scratches , osteomyelitis resulting from direct inoculation or extension of cellulitis, and the combination of septic arthritis and osteomyelitis, most commonly involving a finger or hand after a cat bite. 2. Isolation of P. multocida from the respiratory tract: The isolation of P. multocida from the respiratory tract must be interpreted differently than its isolation from other systemic sites. Most commonly P. multocida found in the respiratory tract is a commensal organism in patients with underlying pulmonary disease, but serious respiratory tract infections including pneumonia, empyema, and lung abscesses may develop. Most patients with respiratory tract colonization or infection have a history of animal exposure. 3. Other systemic infections: P. multocida is recognized as a pathogen in a variety of systemic infections including bacteremia, meningitis, brain abscess, spontaneous bacterial peritonitis, and intra-abdominal abscess. P. multocida often acts as an opportunistic pathogen with a predilection for causing bacteremia in patients with liver dysfunction, septic arthritis in damaged joints, meningitis in the very young or elderly, and pulmonary colonization or invasion in patients with underlying respiratory tract abnormalities.(ABSTRACT TRUNCATED AT 400 WORDS)

Abscess↗
PubMed1983

Naturally occurring non-T suppressor cells in pregnant and neonatal mice: some functional and phenotypic characteristics.

The mammalian fetus thrives in the presence of a maternal immune system which is considered capable of initiating an aggressive reaction against alloantigens expressed on fetal cells. The control of harmful immunological reactions during pregnancy may be due in part to the combined action of soluble immunoregulatory factors and suppressor cells in the maternal/fetal environments. In the present investigation, a comparison has been made between naturally occurring splenic suppressor cells isolated from neonatal and pregnant adult CBA/J mice. Functional analysis of inhibitory activity was carried out using conventional one-way allogeneic mixed lymphocyte reactions (MLR) consisting of adult CBA/J spleen cells responding against mitomycin C-inactivated BALB/cJ spleen cells. Suppressor cells in the spleen of pregnant animals as well as a population of inhibitory cells in newborn spleen could be shown to be highly resistant to cytotoxic pretreatment with anti-T cell serum plus complement. Both newborn and pregnant non-T suppressor cells were shown to be agglutinated by the B cell-specific lectin soybean agglutinin. The densities of these two populations of non-T inhibitory cells, as determined by Percoll gradient centrifugation, were demonstrated to be very similar (ie, within the range of 1.067 to 1.043 g/ml). The striking parallels in the functional and phenotypic characteristics of the non-T suppressor lymphocytes found in the spleen of pregnant and neonatal animals suggest a common mechanism for their induction.

Animals↗
PubMed1983

Rapid method for screening large numbers of Escherichia coli colonies for production of plasmid-mediated beta-lactamases.

A rapid, simple assay for screening large numbers of Escherichia coli colonies for production of certain plasmid-mediated beta-lactamases (including TEM-1, TEM-2, HMS-1, SHV-1, OXA-1, PSE-1, PSE-4, and CEP-2) is described. The technique, a modification of the method of Slack et al. for detection of beta-lactamase in limited numbers of Haemophilus influenzae clinical isolates (Lancet ii:906, 1977), uses filter paper impregnated with benzylpenicillin and a pH indicator dye (bromocresol purple) that changes color in the presence of beta-lactamase activity. The test paper is briefly applied to an agar surface containing bacterial colonies which are subsequently scored individually on the paper by color: yellow indicates the presence of beta-lactamase, dark green its absence, and variegation (yellow and dark green) a mixed population. Concordance of the results of this assay with those of replica plating for antibiotic resistance was over 99%. Hundreds of colonies per plate can be scored quickly and remain viable for further evaluation. The assay appears to be useful for studies of the stability of plasmids encoding beta-lactamases and in cloning with vectors such as pBR322 in which insertion of DNA fragments can be detected by inactivation of the beta-lactamase gene. Whenever the assay is to be used, results should always be confirmed initially by another method, such as replica plating, because the test paper assay does not detect three beta-lactamases (OXA-2, OXA-3, and PSE-2) and also would miss intrinsic penicillin resistance.

Drug Resistance, Microbial↗
PubMed1983

Novobiocin-induced elimination of F'lac and mini-F plasmids from Escherichia coli.

Novobiocin eliminated (cured) F'lac and three low-copy-number mini-F plasmids (pML31, pMF21, and pMF45) from Escherichia coli to different extents. F'lac was cured 0 to 3%. pML31, whose replication region is contained on the 9-kilobase f5 EcoRI restriction enzyme fragment of F, was eliminated 10 to 92%. pMF21, deleted of the origin of mini-F replication at 42.6 kilobases on the F map and known to initiate from an origin at 45.1 kilobases, and its closely related derivative pMF45 were cured to the greatest extent (greater than 97%). pMF45 was eliminated from a wild-type bacterial strain but not from an isogenic novobiocin-resistant gyrB mutant strain, indicating involvement of the B subunit of DNA gyrase in the curing phenomenon. The number of bacteria containing pMF45 halved with each generation of growth in the presence of novobiocin, as is predicted for complete inhibition of plasmid DNA replication.

DNA Replication↗
PubMed1983

Circulating immune complexes in prosthetic valve endocarditis.

Using the Raji cell radioimmunoassay, we have determined circulating immune complex (CIC) levels in 36 patients with prosthetic valves during 38 episodes of fever. Fever resulted from prosthetic valve endocarditis (PVE) in 27 instances and from other causes in 11 instances. Peak initial CIC levels higher than 100 micrograms/mL occurred more frequently in the group with PVE, while peak initial CIC values less than 30 micrograms/mL were more frequent in the control group. Circulating immune complex levels fell substantially with completion of antibiotic therapy in 28 (78%) of the patients with PVE. Late CIC elevations were associated with drug-related rashes and replacement of persistently infected prostheses. Our data suggest that the predictive value of measurement of CIC levels in patients with fever and prosthetic valves is in excluding PVE in patients with CIC levels persisting below 30 micrograms/mL.

Antigen-Antibody Complex↗
PubMed1982

Effects of novobiocin, coumermycin A1, clorobiocin, and their analogs on Escherichia coli DNA gyrase and bacterial growth.

Novobiocin, coumermycin A1, and clorobiocin, structurally related compounds that antagonize the B subunit of the essential bacterial enzyme DNA gyrase, were compared with 18 of their analogs for the inhibition of Escherichia coli DNA gyrase supertwisting activity in vitro and of bacterial multiplication. This family of compounds has a 4-hydroxy-8-methylcoumarin core substituted in the 7 and 3 positions. Important for enzyme inhibition in vitro is a 7 ether linkage to a 3'-substituted noviose sugar. The 3'-ester-linked 5-methylpyrrole, found in the coumermycin series, conferred at least 10-fold more inhibitory activity than did the similarly linked amide, found in the novobiocin series; lack of the pyrrole and amide results in the loss of inhibitory activity. Of many aryl and alkyl substituents linked as an amide at the 3 position, the 4-hydroxyl-3-(3-methyl-2-butenyl)benzoic acid moiety, found in novobiocin and clorobiocin, and the reduplication of the coumarin-noviose-5-methylpyrrole, found in coumermycin A1, were most effective in gyrase inhibition. In vivo, the ability of these compounds to inhibit the growth of E. coli varied greatly. The enhanced inhibition of gyrase in vitro conferred by a 5-methylpyrrole relative to an amide in the 3'-noviose position was reflected in inhibition of bacterial multiplication. Several substitutions at the 3 position of the coumarin core conferring similar antagonism of gyrase in vitro resulted in substantially different inhibitory activities for E. coli, suggesting that these moieties at the 3 position affect drug access to the intracellular target. This target was shown for isobutyryl PNC-NH2 (PNC-NH2 is 3-amino-4-hydroxy-8-methyl-7-[3-O-(5-methyl-2-pyrrolylcarbonyl)noviosyloxy] coumarin) and confirmed for novobiocin, coumermycin A1, and clorobiocin to be in the B subunit of DNA gyrase.

Aminocoumarins↗
PubMed1982

Antagonism of the B subunit of DNA gyrase eliminates plasmids pBR322 and pMG110 from Escherichia coli.

The constructed plasmid pBR322 and the native plasmid pMG110 were eliminated (cured) from growing Escherichia coli cells by the antagonism of the B subunit of the bacterial enzyme DNA gyrase. The antagonism may be by the growth of cells (i) at semipermissive temperatures in a bacterial mutant containing a thermolabile gyrase B subunit or (ii) at semipermissive concentrations of coumermycin A1, an antibiotic that specifically inhibits the B subunit of DNA gyrase. The kinetics of plasmid elimination indicate that plasmid loss occurs too rapidly to be explained solely by the faster growth of that plasmid-free bacteria and, therefore, represents interference with plasmid maintenance.

Aminocoumarins↗
PubMed1982

Suppression of primary and secondary autologous mixed lymphocyte reactions by murine alphafetoprotein.

The relatively strong proliferative responses that result from the co-culture of responder T and stimulator non-T cell populations separated from the lymphoid tissues of genetically identical mice have been termed autologous mixed lymphocyte reactions (AMLR). These responses are believed to reflect the normal existence of self reactive T lymphocyte clones which are prevented from establishing pathological autoimmune processes in vivo by the presence of effective regulatory mechanisms. Neonatal thymocytes belonging to the Lyt 1+23-T cell subset are shown here to possess an exceptionally efficient capacity to respond against non-T Ia+ spleen cells from adult mice of the same inbred strain. Moreover, AMLR-primed neonatal thymocytes can be restimulated to give a response with the magnitude and kinetics characteristic of a secondary MLR. Murine AFP, which has been previously demonstrated to exert highly selective immunoregulatory effects on allogeneic MLR, is shown here to be capable of essentially abrogating primary and secondary AMLRs in concentrations that can be considered physiological with respect to the endogenous serum AFP levels in the fetus and newborn. Purified AFP isolates of human and rat origin were also demonstrated to have significant inhibitory effects on the murine AMLR. We therefore suggest that endogenous levels of AFP in the fetus and newborn may play an important role in the control of autoreactive lymphocyte functions. Consistent with this idea is the finding that neonatal thymocyte AMLR activity disappears with increasing age in parallel with normal physiological decay in serum AFP levels.

Age Factors↗