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Biomedical subjects

C P Davis

Publications and source records attributed to C P Davis.

90 records · Page 5Linked to original sources
PubMed1979

Properties of a gonococcal inhibitor produced by Escherichia coli.

Strains of Escherichia coli can inhibit the in vitro growth of Neisseria gonorrhoeae. One E. coli strain released a potent agar-diffusible gonococcal growth inhibitor which was extracted and assayed in an agar well assay system. The culture conditions necessary to produce the inhibitor were determined. The inhibitor was bacteriostatic, in most cases, for N. gonorrhoeae. Based on ultrafiltration and column chromatography, the inhibitor appeared to have a molecular weight in the range of 1200 to 2000. Evidence that the molecule contained charged sites was obtained by membrane binding and column chromatography. The inhibitor was stable to extremes of heat, cold and pH. It was not volatile or susceptible to proteolytic enzymes, lysozyme, lipase, DNAase, RNAase or certain chelating agents. Its activity was completely blocked by ferric ammonium citrate. This inhibitor is dissimilar to previously reported gonococcal inhibitors of bacterial origin.

Escherichia coli↗
PubMed1979

Evidence for pili-mediated adherence of Klebsiella pneumoniae to rat bladder epithelial cells in vitro.

The possible role of pili in the pathogenesis of urinary tract infections caused by Klebsiella pneumoniae was studied in an in vitro mixture of a phosphate-buffered saline suspension of rat bladder epithelial cells and phosphate-buffered saline-washed K. pneumoniae. Nonpiliated and piliated populations derived from a single K. pneumoniae strain were obtained by controlling the total time of growth in broth medium. The piliated phase demonstrated a significant increase in adherence when compared to the nonpiliated phase. Incubation of the bacteria and epithelial cell mixture at 4 and 37 degrees C resulted in no differences in adherence; optimal adherence occurred at pH 5. Pretreatment of the bacteria with enzymes to destroy the pili resulted in a decrease in adherence, as did killing the bacteria by various means before adherence testing. Pretreatment of the epithelial cells with certain saccharides inhibited bacterial adherence. Finally, a 96% decrease in adherence was observed after coincubation of bacteria and epithelial cells with papain-treated antipili antibodies. Thus, it appears that pili on the surface of K. pneumoniae mediate attachment of the bacteria to rat bladder epithelial cells.

Adhesiveness↗
PubMed1979

The response of the renal pelvis to infection: a scanning electron microscopic study.

The response of the rat renal pelvis to Pseudomonas aeruginosa infection was examined using scanning electron microscopy. Bacterial attachment was noted in regions of microplical alteration with subsequent strand formation and epithelial cell exfoliation. These observations support the hypothesis that bacterial invasion initiates defense mechanisms in the renal pelvis similar to those noted in bladders, namely, membrane alteration with increased bacterial attachment, strand formation with further bacterial entrapment, and exfoliation of bacteria-laden epithelial cells which are eliminated via voiding.

Animals↗
PubMed1977

Bacterial association in the gastrointestinal tract of beagle dogs.

Nine male beagle dogs, housed in either a conventional or locked environment for 2.5 years, were killed, and the bacterial flora present in various regions of each gastrointestinal tract was assessed by culture techniques, light microscopy, and scanning electron microscopy. All dogs possessed a complex microflora in their colons; in almost every dog anaerobes predominated. The highest number of bacteria cultured was 10(10)/g (dry weight) of tissue and contents; highest counts obtained with a Petroff-Hauser counting chamber were 10(10)/ml (wet weight). Although there was a consistency in the detectable genera, there were also noticeable differences in the flora of dogs housed under different environmental conditions. These differences included qualitative and quantitative changes in the flora as well as alterations in the distribution and localization of microorganisms along the gastrointestinal tract and in the crypts of Lieberkuhn. No bacterial layers were detected on the surfaces of stomach or proximal bowel in any of the dogs. Dogs housed in a conventional, open, environment had bacteria that occurred in layers on their ceca and colons and in their crypts of Lieberkuhn; however, dogs housed under "locked" environmental conditions did not possess them or had them less frequently. Dogs removed from the locked environment and kept (30 days) in conventional housing conditions were the only ones with detectable segmented filamentous microbes in their ilea. This study shows that the microbial flora does not simplify when dogs are housed in a locked environment. Indeed, it may increase in complexity and cause alterations in the bacterial flora that is associated closely with gastrointestinal epithelial cells and crypts of Lieberkuhn.

Aerobiosis↗
PubMed1977

Bladder response to klebsiella infection: a scanning electron microscopy study.

The early response of rat bladder epithelium to Klebsiella pneumoniae was examined using scanning electron microscopy. Increased bacterial adherence with time after challenge paralleled the occurrence of strand formation and ulceration on the bladder epithelium. The early bladder response to the bacteria consisted of altered epithelial membrane structure, strand formation, and exfoliation of some epithelial cells. These observations indicate that K. pneumoniae causes alterations in the bladder epithelium which may trigger an intrinsic bladder defense mechanism consisting of strand entrapment of bacteria, epithelial cell exfoliation, and elimination of attached bacteria via voiding.

Animals↗
PubMed1976

Preservation of gastrointestinal bacteria and their microenvironmental associations in rats by freezing.

The use of frozen rat gastrointestinal tissue samples for both the recovery of viable bacteria and for observation of microbial communities associated with the tissue was investigated. A decrease of 1 log in lactobacilli, bifidobacteria, and anaerobes was observed when the numbers of bacteria recoverable from frozen tissue (stored 7 to 9 days) were compared to those recoverable from fresh nonfrozen tissue (zero time control). However, freezing did not appear to decrease the numbers of recoverable coliforms. Tissues, cleaved with razor blades after being frozen and stored for 7 to 9 days, showed bacterial communities situated on the mucosa and in the lumen of gastrointestinal specimens. This freezing technique preserved structures not previously observed in the gastrointestinal tract. This indicates that freezing is a good method to use to study such fragile microenvironments.

Anaerobiosis↗
PubMed1976

Effect of penicillin on the succession, attachment, and morphology of segmented, filamentous microbes in the murine small bowel.

Indigenous segmented filamentous microbes attach to murine ileal epithelial cells. These microbes can be seen on the epithelial surface with a scanning electron microscope. They colonize preferentially the distal ileum in mice. Penicillin, placed in the animal's drinking water, eliminates the microbes from the mouse ileum, but recolinization of the ileum is observed 4 to 5 weeks after the penicillin treatment is stopped. Within 3 to 5 h after rats are given penicillin, the morphology of the microbes is changed. Their external surfaces are wrinkled or broken. Vacated and partially vacated attachment sites are observed. Almost all of the organisms disappear from murine ilea after the animals are exposed to penicillin for 10 h. These observations are discussed in relation to the microbe itself and in its interaction with ileal epithelial cells.

Animals↗
PubMed1974

Habitat, succession, attachment, and morphology of segmented, filamentous microbes indigenous to the murine gastrointestinal tract.

Some indigenous microorganisms localize on epithelial surfaces in various areas of the digestive tracts of animals. One of these, a segmented, filamentous microbe, localizes on the epithelium in the small bowels of mice and rats. These filamentous microbes colonize mice at weaning time and persist in adult animals for at least 2 months. Results of the study of light and electron micrographs suggest that the microorganisms are procaryotic, and that they interact with small bowel epithelial cells to form an attachment site. This site consists of modified epithelial cell membrane and apical cytoplasm adjacent to the attached bacterium. The microbe fills the site with part of its first segment. This segment has a nipple-like appendage on the end inserted into the epithelial cell. The other segments, which compose the rest of the filament, are usually separated by septa. Many of the individual segments contain intrasegmental bodies that appear to be procaryotic cells. Some of these intrasegmental bodies are similar in morphology to the first segment of each filament inserted into an epithelial cell. These intracellular bodies may be components in the life cycle of the microorganism. The organism has not yet been cultured in recognizable form. Therefore, such a hypothesis cannot be proved as yet, nor can the microbe be classified with certainty. Because it localizes in an epithelial habitat in the small bowel, however, it may be a particularly important microbial type in the gastrointestinal ecosystem of laboratory rodents.

Animals↗
PubMed1973

Microbial colonization of the intestinal epithelium in suckling mice.

Colonization by indigenous microorganisms of the mucosal epithelia of the large bowels of suckling mice was followed by microbial culture techniques and by light, fluorescence, and electron microscopy. Certain microbes colonize in distinctive patterns the cecal and colonic epithelia in these mice. Coliforms and enterococci colonize the large bowel 7 to 9 days after birth and reach high population levels during the second week. During that period, these facultative anaerobes can be detected by immunofluorescence techniques in microcolonies in the mucin on the epithelium. During the third week, however, after their populations decline to the low levels characteristic of adult mice, coliforms and enteroccoci can be observed only infrequently in the mucous layer. Anaerobic fusiform-shaped bacteria appear in the mucous layers along with the microcolonies of enterococci and coliforms during the second week after birth. These anaerobes increase in numbers in the mucin until they form thick layers on the mucosal epithelium by the end of the third week. They remain in the mucous layer throughout the life of the normal mouse. Anaerobic spiral-shaped microbes also colonize the mucous layer on the cecal and colonic epithelium. But these organisms can be detected by immunofluorescence in 1-week-old mice, well in advance of the time the fusiform-shaped bacteria can be found. In the second week, the latter microbes co-inhabit the mucous layer with the spiral-shaped organisms. The fusiform- and spiral-shaped microbes remain associated in the mucin on the cecal and colonic mucosal epithelia into the adult life of mice.

Animals↗
PubMed1972

Location and description of spiral-shaped microorganisms in the normal rat cecum.

Some indigenous microorganisms have been shown to localize in certain anatomical sites of the digestive tract of mammals. We studied the ceca of normal adult rats by light and electron microscopy to determine whether any specific bacterial population localizes in this area. All rats studied showed that the crypt was packed with organisms whose morphological character differs from those of the cecal lumen. Organisms localized in the crypt were often identified topographically close to the microvilli of the epithelial cells. These organisms could be differentiated into three types according to their characteristic ultrastructure. Type 1 was a thin spiral-shaped microbe that resembled a Borrelia. Type 2 possessed helically coiled fibers and flagella-like appendages. Type 3 was spiral-shaped but lacked axial fibers. Types 1 and 2 were both capable of penetrating through the crypt epithelium into the lamina propria where they were found in either phagocytes or extracellular locations. These observations are discussed in relation to other host-microflora localization patterns.

Animals↗
PubMed1971

Anaerobic bacteria on the mucosal epithelium of the murine large bowel.

Anaerobic bacteria can be detected at population levels of 10(11) organisms per g of cecum or colon in adult mice from four different colonies widely spaced in the United States. Most of these microorganisms are oxygen-intolerant fusiform-shaped bacteria. At least one type of these tapered, rod-shaped bacteria can be seen in layers in the epithelial mucin in frozen-section histological preparations of the large bowels of mice. In addition, such microorganisms can be seen within 0.5 mum of the epithelium in ultrathin sections of colon or cecum examined in an electron microscope. These fusiform-shaped bacteria predominate in the mucin layers. However, spiral-shaped microorganisms can be found as well near the mucosal epithelia in ultrathin sections of colon. Also, such organisms can be seen in negatively-stained preparations of washings of the colonic mucosal epithelia examined in an electron microscope. At least three types of spiral-shaped organisms, including both spiral-shaped bacteria and spirochetes, can be found in preparations from mice from three of the four colonies. Such spiral-shaped microorganisms can be detected at population levels as great as 10(9) organisms per g of cecum or colon in anaerobic cultures of the large bowels of mice from all four colonies. One anaerobic spiral bacterium was isolated in pure culture. This particular organism was found by immunofluorescence to be intermingled with the fusiform-shaped bacteria in the mucin on the mucosal epithelium in the mouse large bowel.

Anaerobiosis↗
PubMedDate not supplied

Single-shot versus interleaved echo-planar MR imaging: application to visualization of cardiac valve leaflets.

Visualization of the cardiac valves with standard magnetic resonance (MR) imaging is not adequate because of long acquisition times. Echo-planar imaging (EPI) can, however, be performed with a temporal resolution (30-50 msec) comparable to that of echocardiography. The authors evaluated the feasibility of real-time imaging of cardiac valve motion with ultrafast MR techniques. Eight healthy volunteers and three patients with mitral stenosis and regurgitation were studied with a 1.5-T whole-body imager. Two different EPI sequences were assessed: a standard single-shot gradient-echo EPI (GEPI) sequence and a fast imaging technique based on multiple-shot EPI with interleaved k-space acquisition (IGEPI). Fat-suppressed images with an in-plane resolution of 3.7 x 3.7 mm were obtained equally spaced through the cardiac cycle. Half-k-space acquisition was used. Morphologic evaluation was superior with IGEPI, owing to the better intracavitary signal homogeneity (P < .01), and the mitral valve leaflets were easier to identify on systolic images. IGEPI provided adequate valve visibility in all three patients.

Adult↗
PubMedDate not supplied

Phytophotodermatitis: the other "lime" disease.

Phytophotodermatitis is a skin eruption that occurs after contact with photosensitizing compounds in plants and exposure to UV light. There are two common presentations of phytophotodermatitis. Acutely, erythema and vesiculation similar to a severe sunburn are noted. After resolution of the inflammation, the involved skin has marked hyperpigmentation. Many plants have been identified that contain furocoumarins (psoralens), including limes, lemons, and celery. We present a patient with an acute phototoxic eruption and hyperpigmentation after contact with limes during a beach vacation.

Adult↗
PubMedDate not supplied

Postprocessing techniques for gadolinium-enhanced three-dimensional MR angiography.

Contrast material-enhanced three-dimensional (3D) magnetic resonance (MR) angiography is rapidly gaining acceptance as a versatile noninvasive alternative to conventional angiography. The technique has proved useful in the visualization and assessment of complex pathologic entities in the thoracic and abdominal aorta, renal arteries, pelvic arterial system, and pulmonary arteries. Several postprocessing techniques are available for reformation of the imaging data, including maximum intensity projection (MIP), surface rendering, and virtual intraluminal endoscopy (VIE). MIP and subvolume MIP reconstructions can be produced quickly and are useful for demonstration and archiving purposes. Because of its unique ability to display vessels without overlap, surface rendering is especially useful in depicting diseases that influence either the outer shape of the vessels or their topographic arrangement. VIE allows assessment of the inside of the vascular wall and is helpful in detecting wall-bound thrombus and evaluating the degree of stenosis. Most clinically relevant questions (eg, presence of pulmonary embolism, aortic aneurysm, renal artery stenosis) can be fully answered if analysis is based on MIP and thin multiplanar reformations of contrast-enhanced 3D MR angiograms. In some cases, the use of additional postprocessing techniques enhances diagnostic confidence.

Aorta↗
PubMedDate not supplied

Scanning electron microscopy of alcohol-fixed cytopathology specimens.

Cells in specimens fixed in alcohol and stained by the Papanicolaou method for routine cytodiagnosis were subsequently studied by scanning electron microscopy (SEM) to determine if they manifested topologic features described in specimens prepared for optimal SEM observation. In normal bronchial washings, ciliated columnar cells were obvious, and microridges were detected in several squamous cells. Microvilli, although sometimes coarse and blunted, were present in cells of adenocarcinoma, squamous carcinoma and malignant mesothelioma in fluid specimens. Benign histiocytes in bronchial washings, neuroblastoma cells in a smear of bone marrow aspirate and lymphocytic lymphoma cells in spinal fluid had ruffled surfaces. Should topologic features prove to be diagnostically significant, SEM may be of value in further studying equivocal specimens even though they were previously prepared for routine light microscopic observation.

Adenocarcinoma, Bronchiolo-Alveolar↗