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Biomedical subjects

L M Keith

Publications and source records attributed to L M Keith.

15 recordsLinked to original sources
PubMed2001

Genetic divergence in the algT-muc operon controlling alginate biosynthesis and response to environmental stress in Pseudomonas syringae.

The algT-muc gene cluster (rpoE operon) is important for alginate production and survival during environmental stress in Pseudomonas syringae. The algT-muc operon was cloned and sequenced from P. syringae to determine whether the organization of this gene cluster was conserved in this plant pathogen. Interestingly, analysis of the algT-muc region in P. syringae revealed a unique arrangement when compared to other bacteria and lacked a mucC homologue. The relative importance of the mucC gene in the algT (rpoE) operon of various bacterial species is discussed.

Alginates↗
PubMed1999

dnaK and the heat stress response of Pseudomonas syringae pv. glycinea.

The dnaK gene from Pseudomonas syringae pv. glycinea PG4180 was cloned and sequenced. The dnaK coding region was 1,917 bp and contained a putative sigma 32 heat shock promoter 86 bp upstream of the translational start site. grpE, another heat shock gene, was found immediately upstream of the putative dnaK promoter. The predicted amino acid sequence of dnaK showed relatedness to the ATPase and substrate binding domains commonly found in heat shock proteins, as well as the highly conserved signature sequence motifs belonging to the Hsp70 protein family. Furthermore, the PG4180 dnaK gene complemented an Escherichia coli dnaK mutant for growth at temperatures above 37 degrees C, indicating that a fully functional dnaK homologue had been cloned from P. syringae pv. glycinea. All attempts to eliminate dnaK function by insertion mutagenesis failed, possibly because DnaK performs essential functions in P. syringae pv. glycinea. Expression of dnaK in P. syringae pv. glycinea PG4180 was investigated by constructing dnaK::uidA transcriptional fusions; expression of dnaK increased markedly when cells were preincubated at 18 degrees C and then shifted to 35 degrees C. An anti-DnaK monoclonal antibody was used to detect DnaK; in P. syringae pv. glycinea race 4, DnaK levels followed cell density during a 6-h incubation at 26 degrees C. When cells were shifted from 26 degrees C to either 32 or 38 degrees C, DnaK levels increased transiently, and then decreased rapidly. Although the cells continued to grow when incubated at 32 degrees C, growth was not supported at 38 degrees C. Our results indicate that P. syringae pv. glycinea responds to heat shock by producing DnaK, but DnaK does not aid in acclimation to sustained elevated temperatures.

Amino Acid Sequence↗
PubMed1999

AlgT (sigma22) controls alginate production and tolerance to environmental stress in Pseudomonas syringae.

Pseudomonas aeruginosa and the phytopathogen P. syringae produce the exopolysaccharide alginate, which is a copolymer of D-mannuronic and L-guluronic acids. One of the key regulatory genes controlling alginate biosynthesis in P. aeruginosa is algT, which encodes the alternate sigma factor, sigma(22). In the present study, the algT gene product from P. syringae pv. syringae showed 90% amino acid identity with its P. aeruginosa counterpart, and sequence analysis of the region flanking algT in P. syringae revealed the presence of nadB, mucA, and mucB in an arrangement virtually identical to that of P. aeruginosa. An algT mutant of P. syringae was defective in alginate production but could be complemented with wild-type algT from P. syringae or P. aeruginosa when expressed in trans. The algT mutant also displayed increased sensitivity to heat, paraquat, and hydrogen peroxide (H(2)O(2)); the latter two compounds are known to generate reactive oxygen intermediates. Signals for activation of algT gene expression in P. syringae were investigated with an algT::uidA transcriptional fusion. Like that in P. aeruginosa, algT transcription in P. syringae was activated by heat shock. However, algT expression in P. syringae was also stimulated by osmotic stress and by exposure to paraquat, H(2)O(2), and copper sulfate. The latter two compounds are frequently encountered during colonization of plant tissue and may be unique signals for algT activation in P. syringae.

Alginates↗
PubMed1984

Isolation of pigmentation mutants of the green filamentous photosynthetic bacterium Chloroflexus aurantiacus.

Mutants deficient in the production of bacteriochlorophyll c (Bchl c) and one mutant lacking colored carotenoids were isolated from the filamentous gliding bacterium Chloroflexus aurantiacus. Mutagenesis was achieved by using UV radiation or N-methyl-N'-nitro-N-nitrosoguanidine. Several clones were isolated that were deficient in Bchl c synthesis. All reverted. One double mutant deficient both in Bchl c synthesis and in the synthesis of colored carotenoids under anaerobic conditions was isolated. Isolation of a revertant in Bchl c synthesis from this double mutant produced a mutant strain of Chloroflexus that grew photosynthetically under anaerobic conditions and lacked colored carotenoids. Analysis of pigment contents and growth rates of the mutants revealed a positive association between growth rate and content of Bchl c under light-limiting conditions.

Anti-Bacterial Agents↗
PubMed1983

Saphenous vein stripping and its complications.

Saphenous vein stripping is one of the most common general surgical operations. Complications are rare and seldom serious; they can be fur- ther minimized by careful patient selection and meticulous technique. Adherence to the basic principles described should help further reduce the complication rate and maximize therapeutic benefit.

Adult↗
PubMed1979

Parietal cell autoantibodies and hypergastrinemia in achlorhydria and the Zollinger-Ellison syndrome.

Parietal cell autoantibody (PCA), basal gastrin, and calcium-stimulated gastrin were measured in twenty patients with achlorhydria, in eight patients with the Zollinger-Ellison syndrome, and in fifty control subjects. In twelve patients with achlorhydria with a spared antrum, PCA was positive and basal gastrin was elevated. In contrast, eight achlorhydric patients with antral gastritis had negative PCA and significantly lower basal gastrin levels. Patients with the Zollinger-Ellison syndrome did not demonstrate positive PCA despite elevated levels of basal gastrin, nor was PCA present in normal controls. This study suggests that certain achlorhydric states are caused by an autoimmune response, particularly if antral function is spared.

Achlorhydria↗
PubMed1979

Use of Doppler ultrasound in intestinal surgery.

Doppler ultrasonography was used intraoperatively in 117 patients undergoing intestinal anastomosis or enterostomy to determine the adequacy of blood supply at the margins of resection. Doppler findings were compared with clinical assessment of intestinal blood flow by the operating surgeon. In 92 per cent of cases, Doppler signals and clinical observation coincided. However, in five of six cases in which Doppler signals were absent at one margin, the surgeon resected additional intestine, selecting margins within 1 cm of the nearest arterial Doppler signal. All five patients had uneventful healing. In the one case in which the surgeon chose to rely onthe appearance of the bowel despite the absence of Doppler arterial signals, ischemic necrosis of the proximal segment and anastomotic disruption occurred. The technique of Doppler ultrasonography is readily learned, and the instrument is available in most hospitals. Intraoperative use of Doppler ultrasonography can help identify intestine lacking a blood supply adequate to assure viability before changes in the appearance of the bowel alert the surgeon to the problem.

Colon↗
PubMed1978

Determination of viability of ischemic intestine by Doppler ultrasound.

Doppler ultrasound was used to determine the viability of ischemic small intestine and to select the optimum point for resection of nonviable bowel. Twenty ischemic segments of small intestine were produced in dogs by ligating the vascular supply. The Doppler ultrasound probe then was used to determine the last point of arterial flow within the bowel wall. The dogs were reexplored after 24 hours. Histological examination of full-thickness biopsies showed the intestine to be normal in all 20 segments at the last audible Doppler signal, and in 19 of the 20 segments at 1 cm distal to the last signal. Progressive degrees of necrosis were observed at 2 and 3 cm distal to the last signal. Twenty-five segments of ischemic intestine were resected in baboons. All resections performed at the last Doppler signal or 1 cm distal to it were normal 1 month later. Of 15 resections performed at 2, 3, and 4 cm distal to the last signal, 10 showed evidence of stricture or anastomotic disruption. Doppler ultrasound is a reliable method for determining the viability of ischemic intestine and for selecting the optimum point for resection of nonviable bowel.

Animals↗
PubMed1978

Villous adenomas of the duodenum.

A patient with multiple villous adenomas of the duodenum is described. Endoscopy plays an essential role in the management of these neoplasms. If no evidence of invasive malignancy is found on multiple endoscopic biopsies, wide local excision is the initial procedure of choice. Invasive malignancy found in either the endoscopic biopsy or the surgical specimen is indication for pancreaticoduodenectomy.

Adenoma↗
PubMed1976

Altered serum gastrin levels in achlorhydric states.

Hypergastrinemia occurs in achlorhydric states if the antrum is not diseased, and evidence has been presented that suggests that antral gastritis diminishes gastrin levels in achlorhydric patients. There is a dramatic gastrin response to calcium challenge in patients with pernicious anemia. Only minimal response was observed in patients with atrophic gastritis. Unlike the response observed in the Zollinger-Ellison syndrome, secretin challenge suppresses gastrin in achlorhydric states. These findings add a new dimension to the utility of serum gastrin determinations.

Achlorhydria↗