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L A Lewis

Publications and source records attributed to L A Lewis.

At least 55 records · Page 3Linked to original sources
PubMed1994

Transposition of IS2 into the hemB gene of Escherichia coli K-12.

Genetic studies of the hemB gene in Escherichia coli have resulted in the recovery of both stable and unstable mutant strains. The stable strains have been shown to result from large deletions. This study demonstrates that unstable strains result from the insertion of transposable element IS2 primarily into the 5' region of the structural gene; the instability results from precise excision of the element, producing strains with both high and low frequencies of reversion. This first report of IS2 insertion into hemB suggests that this gene may be a preferred target for insertion of this transposable element.

Aldehyde Oxidoreductases↗
PubMed1993

Relationships of interns' performances to their self-assessments of their preparedness for internship and to their academic performances in medical school.

This study addressed the questions of whether medical students' cumulative grade-point averages (GPAs) correlate with the performance assessments (overall and in specific areas of competency) that they receive as interns from their internship program directors, and whether the students' self-assessments of preparedness for internship correlate with their internship directors' overall assessments. A questionnaire to assess interns' competencies was developed and sent to the directors of the internship programs of the 283 1990 and 1991 graduates of the Medical College of Georgia School of Medicine who consented to participate in the study (82% of the graduates). Eighty percent of the program directors responded. A similar questionnaire was sent to all 342 of the 1990 and 1991 graduates; 38% provided self-assessments of their competencies and also stated their views on how well prepared they were for their internships. Considering the classes as a group, the mean ratings of the interns' overall competencies by the program directors ranged from 3.7 to 4.3 on a five-point Likert scale (1, unsatisfactory, to 5, outstanding), whereas the interns' ratings of how well they were prepared for their internships (that is, their sense of overall competency) were somewhat lower, ranging from 3.4 to 4.0. The correlations of GPAs with the specific areas of competencies ranged from .28 to .51. The correlation between the mean ratings of the program directors and the mean self-ratings of the interns was .58. The data support the conclusions that medical school academic performance relates significantly to performance in internship and that interns do not rate themselves as highly as their program directors do.

Achievement↗
PubMed1993

Specialty choice: development of a questionnaire.

Determination of factors which influence medical students' choice of a specialty is potentially important for decisions regarding medical school curricular changes that might influence students' specialty choice. Beginning in 1988, we developed and annually revised a specialty choice questionnaire which was administered to the senior class at the Medical College of Georgia School of Medicine from 1988 to 1991. This paper presents reliability and validity data regarding the questionnaire. Validation procedures involved driving a multiple discriminant function to determine the significance of relationships between a variable and choice of a primary care (PC) or non-primary care (NPC) specialty. Structure coefficients for the multiple discriminant functions that were statistically and practically significant were desire for longitudinal patient care opportunities and desire for monetary rewards. Estimates of internal consistency were derived using Cronbach's alpha. Cronbach's alpha coefficients for this item set were 0.71, 0.59 and 0.46 for 1988, 1989 and 1990 respectively. Test-retest coefficients for the 1991 12-item questionnaire ranged from 0.51 to 0.81.

Career Choice↗
PubMed1992

Group I introns within the nuclear-encoded small-subunit rRNA gene of three green algae.

Four group I introns from the nuclear-encoded (18S) rRNA genes of three chlorophycean green algae are described; two are in Dunaliella parva, and one each is in D. salina and Characium saccatum. The introns within the gene in the latter two organisms are located at the sites equivalent to the 5' and 3' introns of D. parva, respectively. All four introns lack open reading frames and are relatively small, 381-447 bp. Both primary- and secondary-structural features place these introns within subgroup IC1 described by Michel and Westhof. Phylogenetic relationships of the three intron-containing taxa and their relatives, as inferred from comparisons of 18S rDNA sequences, suggest that inheritance of the introns along with the gene can account for their present distribution. The discovery of these four introns, in addition to two others known to exist in other chlorophycean green algae, suggests that group I introns within the 18S rRNA gene may be relatively common in the green algae.

Base Sequence↗
PubMed1992

Classification model that predicts medical students' choices of primary care or non-primary care specialties.

To identify factors that influence students to choose primary care or non-primary care specialties, the authors surveyed the 509 graduating students at the Medical College of Georgia School of Medicine in 1988, 1989, and 1990. Using a Likert-type scale, the 404 responding students rated potential influences on their specialty choices from 1, very negative, to 7, very positive. The students choosing primary care specialties were positively influenced significantly more often by their desire to keep options open (85% versus 58%, p less than .001) and their desire for longitudinal patient care opportunities (95% versus 54%, p less than .001). Those choosing non-primary care specialties were more often influenced by their desire for monetary rewards (69% versus 35%, p less than .001) and by their perceptions of lifestyle following residency (74% versus 60%, p less than .01) and prestige of the specialty (57% versus 36%, p less than .001). The authors used multiple discriminant analysis to derive a discriminant function that would permit classification of students into primary care and non-primary care groups. The potential influences of desire for longitudinal care opportunities and desire for monetary rewards were statistically and clinically significant for all three years. Using the discriminant function, the authors correctly classified 81%, 79%, and 78% of the students' specialty choices for 1988, 1989, and 1990, respectively. The authors suggest that addressing the issue of monetary rewards will be necessary before the primary care fields again become attractive to students.

Career Choice↗
PubMed1991

Genetic and molecular analysis of spontaneous respiratory deficient (res-) mutants of Escherichia coli K-12.

Respiratory deficient (res-) mutants of E. coli are slow growing microcolonial, anaerobic, catalase and benzidine negative strains whose broad phenotypic alteration may result from pleiotropic mutations in genes of the hemin biosynthetic pathway. They are easily recovered from platings of sensitive cells on concentrations of gentamicin higher than the minimal inhibitory concentration. These mutants show a dramatic change in their biochemical diagnostic profile resulting primarily from deficiencies in the active transport mechanisms of the cell. Using well-marked F- and Hfr strains, 157 mutants were analyzed from 3 different parent strains; all but 2 resulted from mutations in 3 loci of the hemin biosynthetic pathway. Of these a marked skew to hemB- mutations was seen, with more than 80% mapping there. The possibility that this hot spot resulted from transpositional activity was tested by Southern hybridization of EcoRI digests of the chromosomal DNA, using as a probe, a 2.8-kb fragment containing the hemB gene. The WT and other hemB+ control strains contained a 14.6-kb fragment. Of 18 hemB strains tested, 14 showed deletion and insertion mutations which fell into four classes based on the variation in the size of the fragment or on the absence of hybridization. The latter resulted from complete deletion of the hemB gene. An increase in fragment size from 1.5-kb to 3.4-kb was observed in some of the strains.

Aminoglycosides↗
PubMed1991

Determination of serum cholesterol by isotope dilution mass spectrometry with a benchtop capillary gas chromatograph/mass spectrometer: comparison with the National Reference System's Definitive and Reference Methods.

We developed an isotope dilution mass spectrometric cholesterol method with [25,26,27-13C]cholesterol as internal standard and a benchtop gas chromatograph/mass spectrometer (GC/MS) that is much easier and less time consuming than previously described Reference and Definitive Methods for cholesterol. The internal standard, cholesterol standards, and unknown specimen are delivered volumetrically with an automated dilutor and the saponifying reagent. After saponification, extraction, and derivatization, specimens are injected into a benchtop quadrupole MS with an autosampler. Unknown cholesterol concentrations are calculated automatically by comparing the peak area ratio of the m/z = 368, 371 ion pair with the ratios for the cholesterol standards (0 to 12.93 mmol/L). We found within-run and day-to-day (overall) imprecision of 0.44% and 0.95%, respectively, when specimens were assayed singly. In several lyophilized and frozen Standard Reference Material (SRM) pools, cholesterol results with our GC/MS method averaged 0.4% less than the National Institute for Standards and Technology definitive GC/MS result performed about three years earlier. Our GC/MS results averaged 1.3% and 2.0% less than results by the National Reference System (NRS) Abell-Levy-Brodie-Kendall (ALBK) results from clinical specimens and the SRM pools, respectively. These results are consistent with the previously reported bias between the NRS Reference and Definitive Methods and the 0.1% per year decrease in cholesterol concentrations in SRM pools as determined by GC/MS analysis. These results further emphasize the small but consistent bias between cholesterol results by isotope dilution mass spectrometry and the ALBK Reference Method, the latter being the basis for the National Cholesterol Education Program guidelines and population reference values.

Cholesterol↗
PubMed1990

Characterization of gentamicin-resistant respiratory-deficient (res-) variant strains of Staphylococcus aureus.

Exposure of sensitive cells of Staphylococcus aureus to concentrations of gentamicin higher than the minimal inhibitory concentration, results in the recovery of low level resistant strains with a greatly altered phenotype (variants). Because the phenotypic alteration in these strains is so great the expected diagnostic characterization of these variants as S. aureus is obscured. Starting with a genetically-marked parent strain, a comprehensive cytological, physiological, morphological, genetic and biochemical analysis of the variants isolated from it was carried out. The genetic lineage of the variants to the parent was also established by DNA/DNA hybridization. Variants result from mutations in the hemin biosynthesis locus, the effect of which is to disrupt the synthesis of components of the electron transport system, lipid synthesis and selected nucleotide synthesis. Thus the strains are defective in aerobic and anaerobic respiration, (res-), in active transport of aminoglycosides (which confers low level resistance), export of characteristic exo-enzymes, and in cell wall composition and structure.

Bacteriophages↗
PubMed1990

Reduction of peak inflation and positive end-expiratory pressure using pressure control with inverse-ratio ventilation: a case report.

Pressure control with inverse-ratio ventilation (PcIRV) has been shown to reduce peak inspiratory pressure (PIP) and positive end-expiratory pressure while providing adequate oxygenation and ventilation. This case of a 39-year-old man with a perforated colon who required high PIP after surgery demonstrates the effectiveness of PcIRV in reducing PIP from 72 cm H2O to 44 cm H2O and reducing positive end-expiratory pressure from 24 cm H2O to 6 cm H2O. A maximum inverse ratio of 3:1 was established to achieve a PaO2 of 105 mm Hg and PaCO2 of 37 mm Hg. In this case, the mean airway pressure rose from 32 cm H2O with assist-control ventilation to 39 cm H2O with PcIRV at 3:1. Cardiac output decreased from 9.11 L/min to 8.35 L/min with PcIRV at a 3:1 inspiratory/expiratory ratio.

Adult↗