PubMed Health⌕ Search

Biomedical subjects

D G Chapman

Publications and source records attributed to D G Chapman.

9 recordsLinked to original sources
PubMed1994

Comparison of methodologies used in assessing the postantibiotic effect.

The postantibiotic effect (PAE) of the carbapenem antibiotic meropenem was determined for the reference strains of Escherichia coli NCTC 4174 and E. coli NCTC 12210. Regrowth of bacteria after antibiotic exposure was determined by viable counting and bioluminescence alone and in combination with an impedance technique and a morphological technique was also employed. Different methods of calculating the PAE were also used. After exposure of E. coli to 0.1-100 x MIC of meropenem for 2 h, concentration dependent differences in counts by bioluminescence, and viable counting were observed, the latter always being lower. The unexposed control of E. coli NCTC 4174 yielded counts of 1.1 x 10(6) +/- 1.1 x 10(5) and 1.3 x 10(6) +/- 4.7 x 10(5) by viable counting and bioluminescence respectively and E. coli NCTC 12210 gave counts of 4.2 x 10(6) +/- 1.8 x 10(6) and 1.1 x 10(7) +/- 4.3 x 10(6) by the same methods. After exposure to 100 x MIC of meropenem, NCTC 4174 yielded counts of 1.28 x 10(3) +/- 5.35 x 10(2) and 2.59 x 10(5) +/- 8.61 x 10(4) and NCTC 12210 gave counts of 5.22 x 10(3) +/- 9.74 x 10(2) and 5.21 x 10(6) +/- 1.45 x 10(6) by viable counting and bioluminescence, respectively. The discrepancies were due to the inability of the viable counting procedure to detect spheroplasts. Falsely low post exposure counts led to falsely low determinations of PAE by viable counting alone and in combination with the impedance technique.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Bacterial Agents↗
PubMed1994

Postantibiotic effect of meropenem on members of the family Enterobacteriaceae determined by five methods.

The postantibiotic effect (PAE) of meropenem was determined for 11 strains, both clinical isolates and reference strains of members of the family Enterobacteriaceae. The study compares PAE results obtained by five methods used to monitor bacterial regrowth, including viable counting, alone and in combination with impedance; bioluminescence, alone and in combination with impedance; and a morphological technique. After exposure of the test organisms to meropenem (0.1 x to 100 x MIC) for 2 h, concentration-dependent differences in counts by bioluminescence and viable counts were observed, the latter always being lower. The differences varied with the test organism. For example, after exposure of Providentia stuartii NCTC 10318 to 0.1 x MIC, the counts were 5.5 x 10(5) and 2.0 x 10(5) whereas after exposure of Citrobacter freundii MR76 to 0.1 x MIC of meropenem the counts were 2.3 x 10(6) and 6.8 x 10(3) by bioluminescence and viable counting, respectively. The discrepancies were probably due to the relative inability of the viable counting procedure to detect fragile aberrant morphologies and resulted in differences in the calculated PAE values. With methods which do not detect fragile morphologies, the PAE may be underestimated. A general trend was observed for the order of magnitude of the PAEs by the following methods (in order of decreasing magnitude of PAE): (i) morphological technique, (ii) bioluminescence technique alone, (iii) bioluminescence in combination with impedance, (iv) viable counting in combination with impedance, and (v) viable counting alone. It is our opinion that of the methods examined in this study, bioluminescence in combination with impedance best reflects the true values for PAEs, and these results were examined more closely.

Bacteriological Techniques↗
PubMed1991

The effects of posterior cortical lesions on responses to visual threats in the Mongolian gerbil (Meriones unguiculatus).

Mongolian gerbils received aspiration lesions of either primary visual cortex (PVC), medial extrastriate visual cortex, retrosplenial cortex (RSC), or sham operations. The responses of gerbils to the presentation of an overhead visual stimulus were recorded in an open field. In all groups, presentation of the stimulus produced an increase in rearing. This suggests that the stimulus was detected by all animals. Gerbils with RSC or PVC lesions showed reduced levels of response to the stimulus. We suggest that some of the observed deficits can be explained as failures to produce responses to threat that are appropriate to the context in which the the threat was presented.

Animals↗
PubMed1991

Calibration of retinal image size with distance in the Mongolian gerbil: rapid adjustment of calibrations in different contexts.

Mongolian gerbils were trained to jump from one platform to another across a gap whose size varied randomly from trial to trial. In test sessions, probe landing platforms differing in width from those used in training were used, and the distance that the animals jumped was measured. The first experiment demonstrated that the gerbils learned to calibrate the retinal image size of the landing platform with its distance and that they could learn more than one calibration at a time. The second experiment provided evidence that such calibrations are rapidly adjusted to environmental contingencies. These findings suggest that retinal image size might be a useful distance cue for gerbils in a variety of ecological contexts.

Animals↗
PubMed1984

Tris- and deoxycholate-induced lysis in colistin-treated Proteus strains.

Strains of Proteus spp. were pretreated with colistin (polymyxin E) and resuspended in either Tris buffer or sodium deoxycholate. Leakage of potassium and materials with an absorption maxima at 260 nm increased on resuspension of two pretreated Proteus mirabilis strains in Tris buffer or sodium deoxycholate. The activity of Tris increased up to pH 9 and of sodium deoxycholate up to 1,000 micrograms/ml. Greater leakage occurred with resuspension in Tris buffer than in sodium deoxycholate. Other Proteus strains tested did not produce leakage following similar treatment.

Colistin↗
PubMed1978

Pretreatment with colistin and Proteus sensitivity to other agents.

The effects of pretreatment with colistin (polymyxin E) on the sensitivity of Proteus mirabilis, P. vulgaris and P. morganii strains to tris and sodium deoxycholate (DOC) have been studied. Pretreatment of two P. mirabilis strains (NCTC 60 and 4199) with low concentrations (0.25 approximately 1 microgram/ml) of colistin rendered them sensitive to lysis by tris (0.05M) or DOC (250 approximately 1,000 microgram/ml) although DOC induced lysis of control (non-colistin-treated) suspensions also. In contrast, the other P. mirabilis strains, as well as the P. vulgaris and P. morganii strains were little affected by tris (0.2M) or DOC (10,000 microgram/ml) even after exposure of the cells to high colistin concentrations (up to 500 microgram/ml). Colistin-pretreated or control cells of P. mirabilis NCTC 60 rapidly lost viability when suspended in water but not when held in 0.16M sodium chloride solution. Ethylenediamine tetraacetate-pretreated cells of strains 60 and 4199 were fairly sensitive to tris, although the extent of the lysis was less than when colistin was used as pretreating agent. One strain of P. vulgaris (NCTC 4175) became sensitive to tris and to DOC following exposure of the cells to ampicillin.

Colistin↗
PubMedDate not supplied

Food additives.

Explore the source record for details and available documents.

Canada↗