Methods for studying microbial colonization of plastics.
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Bacteria↗
Biomedical subjects
W A Simpson
Publications and source records attributed to W A Simpson.
Pedestal effect in visual motion discrimination.
Many sensory discriminations, including the discrimination of speed, obey Weber's law and thus become more difficult as the stimuli get larger. Using one-jump apparent motion stimuli, we find that the opposite can occur: displacement discrimination improves with larger jumps. This pedestal effect occurs for small jumps near and below the detection threshold. Finding a pedestal effect in motion discrimination confirms a speed energy model developed in previous experiments on the detection of jump pairs, since the pedestal effect will be observed if the visual system detects the energy of the speed waveform. Once the size of the jumps becomes large enough, the discriminability declines, indicating masking. Masking is just the detectability counterpart of Weber's law; it is not predicted from energy detection. The pedestal effect shows the presence of a squaring nonlinearity for small speed signals, and masking indicates linear transduction for large signals. A half-wave rectifier, when presented with Gaussian noise, behaves this way. The speed energy model can be seen as an approximation, valid for small signals, to a model that includes half-wave rectification.
Humans↗
Temporal summation of visual motion.
The sensitivity of the visual system to changes in velocity over time was investigated using the approach that Rashbass [(1970) Journal of Physiology, 210, 165-186] applied to luminance. Pairs of motion impulses (jumps) were presented, and thresholds for discriminating these pairs of impulses from a stationary display were determined. The results were consistent with a model that posits linear filtering of the input velocity, squaring, and integration over some duration. According to the model, the degree of interaction between the impulses reveals the autocorrelation of the impulse response of the motion system. The data were well fit by a three-element cascade of leaky integrators. In the temporal frequency domain, the visual motion system is a lowpass filter. This means that the visual system is quite insensitive to acceleration.
Discrimination, Psychological↗
Variable fixation of staphylococcal slime by different histochemical fixatives.
A variety of histochemical fixatives were used to compare the fixation of bacterial films produced by a standard slime-producing strain of Staphylococcus epidermidis on plastic tissue culture plates. Some reagents were completely ineffective in fixing the slime layer, whereas others gave variable results. The best alternative to the fixative of the reference method, the potentially explosive Bouin's reagent, was air drying.
Bacteriological Techniques↗
Depth-coded motion signals in plaid perception and optokinetic nystagmus.
When two sine-wave gratings drift in different directions at the same speed behind a circular window, a single coherent plaid is seen rather than one grating sliding over the other. We find that as the stereo depth separation of the two component gratings increases, the probability of seeing a plaid declines. The gain of the slow phase of vertical optokinetic nystagmus (OKN) also falls as the separation of the components increases. When the two grating components are in the same depth plane, the vertical eye velocity is greater than that of either component. This shows that the OKN is being driven by the plaid, whose vertical speed is roughly twice as fast as the components. We conclude that both perception and OKN are fed by the same motion signal, which arises after binocular combination and after plaid synthesis.
Depth Perception↗
The use of different features by the matching process in short-range motion.
The perception of the direction of motion in luminance kinematograms breaks down when the displacement exceeds a few element widths (this limit is called Dmax). When kinematograms whose elements differ only, in hue are used, motion can be seen but performance declines at smaller displacements. The short-range process, once thought to be only a luminance correlator, is thus able to use hue. If the size of Dmax indicates how well a feature stimulates the motion sensors, hue might be said to have an especially weak input to motion sensors. In order to find the relative potency of luminance and hue as bases of the short-range matching process, Dmax for these features was compared to those obtained for kinematograms whose elements differed in phase (T-phase or L-phase) or orientation (/or/). The matching process could use all the features tested. Luminance seems to be the preferred basis for motion matching, with hue and phase (a tie) yielding smaller Dmax and orientation the smallest.
Color Perception↗
Colonial morphology of staphylococci on Memphis agar: phase variation of slime production, resistance to beta-lactam antibiotics, and virulence.
The growth of Staphylococcus epidermidis sensu stricto and Staphylococcus saprophyticus on Memphis agar yielded up to 6 morphotypes with each strain. With S. epidermidis, one morphotype produced slime (rho) but became non-slime-producing (epsilon) at a high frequency. The slime-producing rho variants were methicillin-resistant and more virulent than methicillin-susceptible epsilon variants in an endocarditis model. With S. saprophyticus, phase variation was of higher frequency. Nitrosoguanidine mutagenesis produced a stable blue epsilon form that was more virulent than the parent in a mouse model of urinary tract infection. Mutants with the blue epsilon phenotype differed from gold epsilon parents in a variety of phenotypic properties, including increased resistance to oxacillin. These staphylococcal species have a high frequency of phase variation: Phase variants differ in antibiotic resistance and virulence, which is only partially correlated with suggested virulence factors such as slime production.
Animals↗
Identification of an antigenic marker of slime production for Staphylococcus epidermidis.
The pathogenic Staphylococcus epidermidis strain RP62A (ATCC 35984) adheres to smooth surfaces by forming a tenacious bacterial film known as slime. The mechanism of slime production is not known; however, workers in the laboratory of G. Pier (Harvard Medical School, Boston, Mass.) have isolated from RP62A a galactose-rich capsular polysaccharide adhesin (CPA) which mediates the attachment of the organism to smooth surfaces. We have obtained two daughter strains from RP62A that no longer produce slime. One daughter strain, H4A, was obtained by selection for a spontaneous variant; the other strain, HAM892, was obtained by treating growing cultures of RP62A with acriflavin. Using an antiserum generated against whole cells of RP62A, we have examined lysozyme-lysostaphin digests of RP62A, H4A, and HAM892 by double immunodiffusion. The two strains that no longer produced slime no longer produced a particular antigen, which we refer to as the slime-associated antigen (SAA). SAA was also produced by unrelated strains of slime-producing S. epidermidis. SAA was heat and protease stable, had a molecular weight of greater than 50,000, and could be partially purified by chromatographing trypsin-digested material over a Sephadex G-200 column. Chemical analysis of partially purified SAA by gas-liquid chromatography found SAA to be glucose rich (59%) and galactose poor (1.4%). This analysis chemically distinguished SAA from CPA. When tested together by double immunodiffusion with anti-RP62A and anti-CPA antisera, partially purified SAA did not cross-react with CPA. Kinetic studies suggested that SAA is a marker for surface accumulation whereas CPA mediates initial adherence.
Adhesins, Bacterial↗
Differential production of slime under aerobic and anaerobic conditions.
A series of 37 clinical isolates of coagulase-negative staphylococci previously identified as negative for slime production by the tube test were reexamined by the tissue culture plate test under aerobic and anaerobic conditions. None of the strains produced slime under anaerobic conditions; however, five strains (13%) produced slime under aerobic conditions.
Aerobiosis↗
Phenotypic variation of Staphylococcus epidermidis in infection of transvenous endocardial pacemaker electrodes.
Coagulase-negative staphylococci isolated from a patient with a pacemaker electrode infection were extensively evaluated by phenotypic and genotypic characterization. Findings from this evaluation were striking because different colony morphologic subtypes were recovered from blood and resected pacemaker electrodes. Staphylococci from each colony subtype (LBL, LBV, LBP, LBS) were identified as slime-producing strains of Staphylococcus epidermidis sensu stricto. Direct plating of isolates from a restricted electrode revealed a mixture of colony phenotypes when examined on a high-salt, low-glucose medium, Memphis agar. Bacteriophage typing employing 17 different phages and plasmid profile analysis were largely unsuccessful in further characterizing bacterial cells of each of the four colony morphotypes. On the other hand, restriction endonuclease analysis by EcoRI digestion of the chromosomal DNA demonstrated the probable common clonal origin of the four colony phenotypes.
Aged↗
Placental hypoechoic-anechoic areas and infarction: sonographic-pathologic correlation.
High-resolution ultrasound (US) and pathologic analysis were used to define the relationship between placental hypoechoic-anechoic areas, frequently seen in the third trimester, and the clinically significant entity of placental infarction. Placentas were obtained from three groups of patients: those prospectively demonstrating one or more placental hypoechoic-anechoic areas greater than or equal to 1 cm in diameter on third-trimester sonograms (n = 14), those with risk factors for vascular disease (n = 12), and control patients without risk factors (n = 16). Pathologic analysis demonstrated significantly more infarcts in patients with risk factors than in control patients (17 vs three, P = .047). Of a total of 22 infarcts from all three groups, 19 (86%) were isoechoic to viable placenta and therefore not detected with US. The three infarcts identified with US contained hypoechoic or anechoic foci of fibrin or hemorrhage. Of 26 placental hypoechoic-anechoic areas 23 (88%) were decidual septal cysts or intervillous thrombosis without infarction. The authors conclude that nonhemorrhagic placental infarction cannot be identified with ex utero US and, by inference, that prenatal US is probably insensitive for detection of placental infarction.
Female↗
The role of fibronectin binding in the rat model of experimental endocarditis caused by Streptococcus sanguis.
Inactivation of fibronectin (Fn) binding by insertional mutagenesis of Streptococcus sanguis with Tn916 reduces virulence of this bacterium in the rat model of infective endocarditis (IE). Transconjugants were screened for Fn adherence using an ELISA adherence test. One transconjugant had a decreased adherence to immobilized Fn. Southern hybridization demonstrated that the insertion occurred only once in this mutant. The parent strain and mutant strain JL113 were used as challenge strains in a rat endocarditis model. These experiments demonstrated that the mutant had a reduced ability (P less than 0.05) to produce IE. Spontaneous excision of Tn916 from JL113 produced strains identical to both the parental and mutant phenotypes. One strain (JLR-19) that retained the mutant phenotype and one (JLR-15) that regained the parental phenotype for Fn binding were tested for their ability to produce IE. These strains demonstrated that the ability to bind Fn and to produce IE were correlated after Tn916 excision. The reduced virulence of the mutant suggested that adherence of S. sanguis to immobilized Fn plays an important role in the production of IE.
Animals↗
Pilomatrixoma: calcifying epithelioma of Malherbe.
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Adult↗
The ultrastructural pathological features of congenital microcoria. A case report.
We describe the light microscopic, immunohistochemical, and electron microscopic findings in a sporadic case of congenital microcoria in a 72-year-old man with senile cataract. We demonstrated a lack of myofilaments and desmin in the stromal cytoplasmic processes of the anterior pigmented cells of the iris, although other features of muscle differentiation were present in these few surviving cell processes that normally form the pupil dilator muscle. Degenerative changes in anterior pigment cells and iris stromal atrophy were thought to be late secondary features of microcoria. The findings suggest that congenital microcoria results from a defect of intermediate filaments in the terminal fetal stages of differentiation of the anterior pigmented epithelial cell of the iris, with absence of myofilaments and consequent failure of development of a functional dilator pupil muscle.
Aged↗
Human optokinetic nystagmus is linked to the stereoscopic system.
It was previously proposed that a linkage between the optokinetic system and the stereoscopic system in higher mammals serves to allow these animals to selectively stabilize those parts of the visual scene which lie in the plane of convergence as the animals move forward in a three-dimensional world (Howard and Ohmi, 1984). A new procedure is now described by which OKN gain can be measured as a function of the binocular disparity of the stimulus. With vergence locked on a vertical line, the gain of the slow phase of vertical optokinetic nystagmus (OKN) was recorded in four human subjects as the binocular disparity (stereo depth) of the moving display was changed from -3 degrees to +3 degrees. The gain of OKN was found to be inversely proportional to binocular disparity. Evidence for cells in the visual cortex, MT and MST that are sensitive both to visual motion and binocular disparity is reviewed. It is argued that the activity of cells responsive to direction of motion and zero disparity selectively augments OKN and that this enables humans to stabilize the images of parts of the scene in the plane of regard while ignoring competing motion signals arising from other distances.
Functional Laterality↗
Molecular epidemiology of nosocomial, multiply aminoglycoside resistant Enterococcus faecalis.
The prevalence of high-level aminoglycoside resistance among Enterococcus faecalis at the Memphis VA Medical Center was 23.6% (59 of 250 isolates) from October to December 1986. Hybridization to a probe cloned from Ent. faecalis pIP1800 for 6' acetyltransferase-2" phosphotransferase (AAC6'-APH2") was observed in 55 (93.2%) of the resistant isolates and was associated with gentamicin resistance. Hybridization to a probe cloned from Ent. faecalis pJH1 for 3', 5" phosphotransferase type III (APH3', 5" III) was observed in 28 (47.4%) and was associated with streptomycin resistance. Twenty-five of the 32 isolates which were resistant to both gentamicin and streptomycin hybridized to both probes. Cell mating in conjunction with hybridization indicated that the AAC6'-APH2" gene is transferred separately from that for APH3', 5" (III), and the streptomycin resistant gene is cotransferred with the latter. The gentamicin-streptomycin resistant isolates therefore contain genes from two Ent. faecalis plasmids, and resistance to these two antibiotics appears to transfer separately. The genetic homogeneity of these isolates suggests nosocomial transmission of enterococci.
Aminoglycosides↗
Unusual complication of strabismus and lid surgery.
A patient with longstanding dysthyroid eye disease developed a broad adhesion between the globe and the upper eyelid following simultaneous surgery to recess the levator palpebrae superioris and lateral rectus muscles. This unusual complication may have developed as a consequence of failure to suture the conjuctiva of the upper fornix to the tarsus and also due to the prolonged static contact between the resulting adjacent raw areas due to postoperative eyelid traction and pressure dressings. Periods of such contact may have been further prolonged by the action of diazepam, which reduces the peak velocity of saccadic eye movements and suppresses rapid eye movement of sleep. Eyelid surgery should be performed as a separate procedure, under local anesthetic after healing of areas bare of conjunctiva from strabismus surgery utilizing the adjustable suture technique.
Conjunctiva↗
Cutaneous gangrene secondary to focal thrombosis--an important cutaneous manifestation of ulcerative colitis.
We describe a patient who developed cutaneous gangrene secondary to microvascular thrombosis, an uncommon complication of inflammatory bowel disease with potentially serious manifestations.
Colitis, Ulcerative↗