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Biomedical subjects

S M Bell

Publications and source records attributed to S M Bell.

At least 91 records · Page 5Linked to original sources
PubMed1988

Comparison of glycine enhancement with cefoxitin induction of class 1 beta-lactamase production in Enterobacter cloacae ATCC 13047.

The presence of either glycine or cefoxitin in the growth medium resulted in an increase in the beta-lactamase activity of cultures of Enterobacter cloacae ATCC 13047. Although the beta-lactamases produced as a result of either glycine enhancement or cefoxitin induction were identical there were striking differences in the kinetics of beta-lactamase production. The increased production of beta-lactamase which resulted from enhancement by glycine occurred late in the growth cycle whereas, with cefoxitin induction, the maximum production of beta-lactamase occurred early in logarithmic-phase growth. After the peak activity was reached the beta-lactamase activity appeared to decline with both processes. However, the mechanism of the apparent fall in the intracellular beta-lactamase activity was different with glycine enhancement and cefoxitin induction. In glycine enhanced cultures the fall presumably was due to leakage of intracellular beta-lactamase into the culture medium whereas with cefoxitin induced cultures there was dilution of beta-lactamase activity by bacterial protein derived from an increase in cell numbers after the cessation of induction. High extra-cellular levels of beta-lactamase activity were observed in cultures enhanced by glycine, whereas little beta-lactamase activity was detected in the medium when the cultures were induced by cefoxitin. The findings demonstrate that there are considerable differences between glycine enhancement and cefoxitin induction, but a final mechanism common to both processes exists which results in the production of identical beta-lactamases by E. cloacae ATCC 13047.

Cefoxitin↗
PubMed1987

Correlative studies of the hypocholesterolemic effect of a highly activated charcoal.

We have carried out in vitro and animal studies to determine the cholesterol lowering efficacy of activated charcoals vs. cholestyramine. In the in vitro studies, we determined the adsorption capacity (Qm) of cholestyramine and activated charcoals for cholesterol in glacial acetic acid. Mean (+/- SD) Qm's (mg cholesterol adsorbed/gm dry sorbent) decreased in the order Super Char highly activated charcoal (277 +/- 121), Norit USP XX charcoal (33 +/- 10), Acta-Char charcoal (26 +/- 4), Mallinckrodt USP charcoal (26 +/- 10), Norit A charcoal (22 +/- 4) and cholestyramine (0). For the bile salt sodium desoxycholate in ammonia: sodium bicarbonate, pH 8.2, the Qm with cholestyramine was 4641 +/- 2669 and with Super Char was 2814 +/- 667 (p = 0.11). We then contrasted the effect of cholestyramine (1%, added to the diet) and Super Char (1% or 2%) on plasma cholesterol concentrations in rabbits made hypercholesterolemic with a diet containing casein. The percent reductions were 61 in one rabbit fed cholestyramine, 61 and 67 in two rabbits fed 1% Super Char, and 90 in one rabbit fed 2% Super Char. In WHHL homozygous rabbits, reductions in plasma cholesterol from pre-treatment and post-treatment levels, respectively, averaged 52% and 38% with 2% cholestyramine (2 animals), 70% and 43% with 2% Super Char (2 animals), and 70% and 63% with 4% Super Char (3 animals). The effectiveness of cholestyramine in animals that lack functional cellular receptors for low density lipoprotein was unexpected. Super Char charcoal appears to be an effective hypocholesterolemic agent, warranting study in man.

Animals↗
PubMed1986

Murine lymphocyte and embryonal carcinoma cell surface antigens recognised by rabbit anti-murine embryonal carcinoma serum.

Some recent studies have suggested that murine embryonal carcinoma (EC) cells which lack classical H-2 molecules must express some novel class-I-MHC (major histocompatibility complex) type antigens. We have investigated whether rabbit anti-EC sera may recognize such components. Molecules of 40 and 48 kd were immunoprecipitated from EC cells and lymphocytes. The possibility that these molecules may be coded for by genes in the Qa-Tla locus which contains many MHC class-I genes or pseudogenes was investigated. The 40 and 48 kd molecules were not associated with beta 2-microglobulin on EC cells, nor with each other or other molecules through S-S bonds, although they appeared to have intradisulphide structures. Peptide map analysis suggested that the lymphocyte 40 and 48 kd molecules were related to the EC cell 40 and 48 kd molecules. However, these molecules were different from H-2, Ia or Qa-2 molecules from the same mouse strain.

Animals↗
PubMed1986

The effect of casein derivatives on glycine enhancement of beta-lactamase production in Enterobacter cloacae ATCC.13047.

Our earlier work showed that glycine enhancement of class I beta-lactamase production in Enterobacter cloacae ATCC.13047 was greater on Isosensitest Agar than on other laboratory media. In the present study it was demonstrated that Casein Hydrolysate was the constituent of Isosensitest Agar which was necessary for glycine enhancement of beta-lactamase production. Also, a comparison of the effect of casein and casein derivatives on glycine enhancement of beta-lactamase production showed that acid hydrolysis of casein was a prerequisite for glycine enhancement of beta-lactamase production. Enterobacter cloacae ATCC.13047 failed to grow on a medium containing casein, and glycine enhancement of beta-lactamase production did not occur on a medium containing tryptic hydrolysate of casein. The effect on beta-lactamase production of variations in the concentrations of both Casein Hydrolysate and glycine was examined by titration of both components in a chequerboard fashion. Beta-lactamase production was influenced by the concentrations of both Casein Hydrolysate and glycine. This inter-relationship indicated that there was a balance between the concentrations of Casein Hydrolysate and glycine and that alterations in this balance modified beta-lactamase production. The significance of the observations is discussed in relation to the factors which influence glycine enhancement of beta-lactamase production in Enterobacter cloacae ATCC.13047.

Caseins↗
PubMed1986

Enhancement of beta-lactamase production by glycine in Enterobacter cloacae ATCC.13047.

Beta-lactamase production in Enterobacter cloacae ATCC.13047 was enhanced by glycine, and the degree of enhancement was dependent on the concentration of glycine and the medium used. Maximum enhancement occurred with a concentration of 0.05 moles/l of glycine, and of 4 media examined enhancement was greatest on Isosensitest Agar. Enhanced beta-lactamase production evoked by glycine was compared with that following induction by various concentrations of cefoxitin. The amount of beta-lactamase produced under conditions of maximum glycine enhancement was higher than that produced by cultures fully induced by cefoxitin. Other differences in the characteristics of the enhancement of beta-lactamase production by glycine and beta-lactamase induced by cefoxitin suggested that the mechanisms of the 2 phenomena were different. The significance of this finding in terms of the interpretation of in vitro antimicrobial sensitivity tests with beta-lactam antibiotics is discussed.

Aerobiosis↗
PubMed1985

Rat natural killer cell and cytotoxic T cell lysis of H-2-negative murine embryonal carcinoma cells.

H-2-lacking murine embryonal carcinoma (EC) cells have been proposed as universal targets for natural killer (NK) effectors from different species because their killing appeared to be uncomplicated by potential T cell effector mechanisms (Stern, P. L. et al., Int. J. Cancer 1981. 27:679). While some previous studies had shown that murine cytotoxic T cells were unable to lyse EC cells, rat T killers are shown here to be active against these targets and to be distinguishable from NK cells. Percoll density fractionation of rat peripheral blood lymphocytes enriches in parallel for NK-mediated lysis of both EC or YAC target cells. These NK cells unlike T cells, do not mediate lectin-dependent and cell-mediated cytotoxicity (LDCC) of NK-insensitive target cells. This procedure is thought to reveal the total cytolytic potential of stimulated T cell populations, regardless of specificity. In contrast to previous results with mice, we found that allogeneically primed rat cytotoxic T cells can kill murine EC cells in LDCC and, further, that rat cytotoxic T cells, generated by stimulation with mouse spleen cells in vitro, can lyse murine EC cells directly. This demonstration of T cell lysis of EC cells suggests that either there is a novel mechanism of lysis operating without requirement for major histocompatibility complex (MHC) structures, or EC cells express some hitherto unidentified MHC-like structures on their cell surface.

Animals↗
PubMed1985

Mutation of Pseudomonas aeruginosa to piperacillin resistance mediated by beta-lactamase production.

Piperacillin-resistant mutants were detected in each of ten strains of Pseudomonas aeruginosa. The resistance was associated with constitutive production by the strains of high levels of beta-lactamase which was similar in character to the induced chromosomal Id beta-lactamase of the parent strains. This type of mutation to piperacillin-resistance occurred at a low frequency. The beta-lactamase production and piperacillin-resistance were stable on repeated subculture and prolonged storage of the strains.

Mutation↗
PubMed1984

Heterogeneity of rat TCGF defined by Mono P isoelectric focusing.

Interleukin-2 (IL-2) prepared from Con A-activated rat spleen cells was partially purified using hydroxylapatite chromatography (HTP) and chromatofocusing on Mono P. IL-2 eluted in a major peak between 0.1 and 0.25 M NaCl in PBS (purification factor 36-fold) and in a second peak in the high salt elution (purification factor 5-fold). When analysed on Mono P, the major peak was found to resolve into four components with apparent pI values in the range of 7.05-5.80; further activity eluted in the high salt fraction. Similar patterns were observed using high salt eluted activity with minor variations in the apparent pI values. Neuraminidase treatment caused a shift in IL-2 charge towards more basic pI values. This analysis of the multiple species of IL-2 suggests that part of the heterogeneity may be due to variation in the degree of sialylation of the peptide chain.

Animals↗
PubMed1984

Enrichment of rat NK cytotoxicity for H2-negative murine embryonal carcinoma cells by panning and short-term culture in TCGF.

The rat natural killer (NK) cell, defined here by spontaneous lysis of H2-negative embryonal carcinoma (EC) cells, was investigated with respect to its antigenic phenotype. Rat spleen cells were separated by panning into adherent and non-adherent populations after incubation with monoclonal antibodies defining differentiation antigens of rat lymphoid cells. This method achieved considerable NK enrichment in some of the panned populations (for example, W3/13 non-adherent cells, up to 20-fold), but emphasized the heterogeneous surface antigen expression of the NK cell type. These enrichment procedures were used to establish bulk cultures of rat NK cells which increased in specific activity over several weeks when grown in T cell-growth factor (TCGF) and could be cloned in soft agarose.

Animals↗
PubMed1980

Mechanisms of ampicillin resistance in Haemophilus influenzae from respiratory tract.

13 of 100 consecutive isolates of Haemophilus influenza obtained from respiratory specimens over the six months to June, 1979, had diminished sensitivity to ampicillin. 6 of the 13 strains produced beta-lactamase, whilst the remaining 7 had no evidence of this enzyme, either in whole cells or in extracts prepared by sonication. The minimum inhibitory concentration of ampicillin for the penicillinase-negative strains ranged from 1 mg/l to 8 mg/l on repeated testing with a carefully controlled agar-dilution technique. The findings contrast strongly with those of earlier surveys of the sensitivity of respiratory strains of H. influenzae to ampicillin and confirm the existence of two mechanisms of resistance to ampicillin in the species.

Ampicillin↗
PubMed1977

Predicting patients' warfarin requirements.

In 34 patients undergoing anticoagulant therapy with warfarin a close relationship has been observed between the logarithm of the 'Thrombotest' response to a loading dose (10 mg/day for three days) and the maintenance dose required to achieve an anticoagulant response of 8-12% (thrombo-test). This relationship appears to be close enough to enable maintenance dosages to be predicted.

Administration, Oral↗
PubMed1977

Infant crying and maternal responsiveness: a rejoinder to Gewirtz and Boyd.

The criticisms leveled by Gewirtz and Boyd focus on 1 of 6 analyses upon which Bell and Ainsworth based their interpretation of findings--namely, cross-quarter correlations of measures of infant crying and maternal response. It is maintained that these measures were approximate, and that they were independent of each other in cross-quarter correlations. It is also maintained that the statistical procedures were appropriate to a small sample of subjects in naturalistic, longitudinal research. The three "illustrative" cases offered by Gewirtz and Boyd as ways of testing a contrary hypothesis are considered. These cases assumed maternal behavior patterns which, it is argued, do not occur. Finally, other evidence is cited, both from other studies and from within the Bell-Ainsworth paper itself, that supports the interpretation that Gewirtz and Boyd claim to have been unjustified.

Conditioning, Operant↗
PubMed1976

Further observations on the value of oral penicillins in chronic staphylococcal osteomyelitis.

This report confirms after periods of observation of up to nine years, the successful treatment with high oral doses of cloxacillin or phenoxymethylpenicillin of 19 patients suffering from chronic staphylococcal osteomyelits. The antibiotic treatment was closely supervised over long periods, and the satisfactory response initially reported has been maintained in each case. Brief reference is made also to the use of the same treatment in a further 191 patients with chronic staphylococcal bone infection. Observations of the progress of 136 of these patients are continuing. At this stage the response in these patients confirms the value in chronic osteomyelitis of the long-term treatment with these penicillins which was established in the first 19 patients treated.

Administration, Oral↗