Biomedical subjects

H J Beckers

Publications and source records attributed to H J Beckers.

At least 19 recordsLinked to original sources

PubMed2000

Phacotrabeculectomy.

The outcome of combined same-site phacoemulsification, posterior chamber lens implantation and trabeculectomy was retrospectively studied in patients with cataract and moderately controlled glaucoma, with a follow-up of at least 6 months. Primary phacotrabeculectomy without antimetabolites was performed in 74 patients. Mean IOP decreased from 22.8 to 14.3 mm Hg (35.3%). A maximum IOP of 19 mm Hg without glaucoma medication was reached in 66.2%. Mean logMAR visual acuity increased from 0.58 to 0.30. Primary phacotrabeculectomy has been shown to be a safe and effective procedure with good IOP control and rapid visual rehabilitation.

Aged↗

PubMed1996

Effect of chlorhexidine varnish on Actinomyces naeslundii genospecies in plaque from dental fissures.

This study describes the effects of varnish containing 40% chlorhexidine diacetate on Actinomyces naeslundii populations in plaque from human molar fissures. In each of 15 subjects two dental fissures with high levels of mutants streptococci were selected. The experimental treatment consisted of the single application of a small amount of chlorhexidine varnish onto the selected fissures. The varnish was removed 15 min after application. One month after varnish application a significant increase was observed in A. naeslundii counts while the number of mutans streptococci had decreased significantly compared with preexperimental levels. From 85 randomly selected Actinomyces isolates taken from blood agar plates before varnish application, 44% belonged to A. naeslundii genospecies 1 and 56% to A. naeslundii genospecies 2. From 106 isolates taken 1 month after chlorhexidine varnish application, 42% belonged to A. naeslundii genospecies 1 and 58% to A. naeslundii genospecies 2. At baseline 28% of A. naeslundii genospecies 1 strains were catalase-positive, but 1 month after varnish application 4% of the strains were catalase-positive (p < 0.05). It is concluded that chlorhexidine varnish application caused an increase of A. naeslundii in dental plaque, but induced no significant changes in the distribution of the two A. naeslundii genospecies.

Actinomyces↗

PubMed1996

Sympathetic innervation of the rat choroid: an autoradiographic tracing and immunohistochemical study.

The sympathetic innervation of the choroid was investigated by means of the anterograde tracer 3H-leucine, injected into the rostral part of the superior cervical ganglion. The tracer was autoradiographically visualized at the light- and electron-microscopic levels. Labelled unmyelinated fibres were found in the choroid and labelled terminals were observed in close proximity to the smooth muscle cells of arterioles. The labelled terminals contain granular vesicles of different size and clear vesicles; the mitochondria were of the electron-dense type and no cell-to-cell synaptic contacts were observed. In addition, tyrosine hydroxylase immunocytochemistry was performed. Immunostained terminals found in the choroid show ultrastructural features similar to those found in the tracing experiments: granular vesicles of different size, clear vesicles and electron-dense mitochondria. On the basis of previous studies and the present observations, it is concluded that the choroid has a dual innervation, a parasympathetic innervation from the pterygopalatine ganglion and a sympathetic innervation from the superior cervical ganglion. The dual innervation is most likely involved in maintaining the homeostasis of vasodilatation and vasoconstriction in the choroid.

Animals↗

PubMed1994

Peripheral neural circuits regulating IOP? A review of its anatomical backbone.

The peripheral nervous system is classically separated into a somatic division containing both afferent and efferent pathways and an autonomic division composed of efferents only. The somatic afferent division is divided in A- and B-neurons. The B-neurons are supposed to be autonomic afferents as part of a reflex system involved in homeostasis. Recent data obtained by neuronal tracing and immunohistochemical experiments concerning the eye related peripheral nervous system endorse the existence of these peripheral reflex systems. Somatic afferents of trigeminal origin synaptically innervate parasympathetic neurons in the pterygopalatine ganglion. This probably represents a pathway mediating autonomically regulated ocular activity in response to sensory stimulation. In addition, it has been hypothesized that trigeminal sensory nerve fibres have an efferent function in response to noxious stimuli e.g. the ocular injury response. Sympathetic nerve fibres originating in the superior cervical ganglion course through the trigeminal and pterygopalatine ganglion without forming direct synaptic contacts. These fibres, however, contain clusters of vesicles suggesting some kind of interneural communication. Parasympathetic nerve fibres of pterygopalatine origin course through the ciliary ganglion. These nerve fibre terminals also contain clusters of vesicles without direct synaptic contacts. Experimental data concerning the distribution of neuropeptides revealed a more detailed knowledge of the anterior eye segment innervation. These experimental data are subject to some debate. The pros and cons of different techniques are discussed. Neural circuits regulating IOP have long been postulated. The possible role of peripheral reflex systems in the regulation of IOP is discussed.

Anterior Eye Segment↗

PubMed1993

The peripheral and central projections of the Edinger-Westphal nucleus in the rat. A light and electron microscopic tracing study.

The peripheral and central efferent projections of the rostral part of the Edinger-Westphal nucleus in the rat were investigated at the light and electron microscopic level by means of iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin and retrograde tracer injections of Fast blue and Nuclear yellow into the facial nucleus and into the principal olive. Two pathways leaving the rostral part of the Edinger-Westphal nucleus were studied, a peripheral and a central descending pathway. Fluorescent experiments demonstrated that the central pathway fibers originated from distinct individual Edinger-Westphal neurons. These neurons were mainly distributed throughout the rostral part of the Edinger-Westphal nucleus and had fusiform cell bodies. The neurons rarely form collateral projections. The central descending pathway left the Edinger-Westphal nucleus medially and terminated bilaterally in the principal olive, in the subnuclei A, B and C of the inferior olive and ipsilaterally in the medial accessory olive. The central pathway also terminated contralaterally in the lateral parabrachial nucleus, the facial nucleus, the trigeminal brainstem nuclear complex, the lateral reticular nucleus and the rostroventral reticular nucleus. The projection to the facial nucleus provides evidence for the existence of a polysynaptic loop forming the central part of the corneal blink reflex. Projections from the Edinger-Westphal nucleus to the cerebellar cortex or the deep nuclei, as described in cat and primate, could not be confirmed. The peripheral pathway left the Edinger-Westphal nucleus ventrally and terminated on dendrites of ciliary ganglion cells, along smooth muscle cells of ciliary ganglion associated arterioles and in the proximity of ciliary ganglion associated venules. The central and peripheral terminals that originate in the Edinger-Westphal nucleus all had similar ultrastructural features: clear, round vesicles and electron dense mitochondria. The terminals originating from the central descending pathway were often found to be arranged in glomerular-like structures. The central and peripheral terminals made asymmetric synaptic membrane specializations (Gray type one), except terminals innervating the ciliary ganglion associated vessels, which showed no synaptic contacts.

Amidines↗

PubMed1993

Substance P in rat corneal and iridal nerves: an ultrastructural immunohistochemical study.

The distribution of substance P (SP) within the nerve fibers of the rat cornea and iris was studied using electron microscopic immunohistochemistry. Numerous SP-immunoreactive fibers were found throughout the corneal and iridal stroma. The most intense staining was found within varicosities containing numerous vesicles. Similar SP-immunoreactive varicosities were found in fibers in close proximity to the iris sphincter and dilator muscles. On account of previous ultrastructural work the SP-containing fibers and varicosities must be assumed to be of trigeminal origin. Additionally, the distribution of SP and calcitonin gene-related peptide (CGRP) in corneal and iridal fibers of rats is similar, suggesting that CGRP and SP are colocalized and may be coreleased from the same varicosities.

Animals↗

PubMed1993

Facial parasympathetic innervation of the rat choroid, lacrimal glands and ciliary ganglion. An ultrastructural pterygopalatine tracing and immunohistochemical study.

The pterygopalatine parasympathetic innervation of the rat choroid, lacrimal glands and ciliary ganglion was ultrastructurally studied by anterograde 3H-leucine tracing. Numerous unmyelinated fibers and vesicle-containing terminals were labeled in these structures. No direct synaptic contacts were found. In the choroid, similar terminals were immunoreactive to vasoactive intestinal polypeptide (VIP). A regulatory feedback loop within the eye-related peripheral nervous system is endorsed by the present results. The finding of fibers and terminals of pterygopalatine origin in the lacrimal glands agrees with earlier studies in cats and monkeys. In the ciliary ganglion, pterygopalatine terminals most likely influence the ganglion cells by nonsynaptic release of neurotransmitters or neuromodulators including VIP.

Animals↗

PubMed1992

Ultrastructural identification of trigeminal nerve endings in the rat cornea and iris.

Trigeminal nerve terminals in the rat cornea and iris were ultrastructurally identified using anterograde tracing with Phaseolus vulgaris-leukoagglutinin (PHA-L). Electron microscopic immunohistochemistry was used to demonstrate the presence and localization of calcitonin gene-related peptide (CGRP) in cornea and iris. In the cornea and iris, nerve fibers were labelled with PHA-L throughout the stroma. Labelling was most obvious within varicosities, densely packed with mainly clear and a few granular vesicles and containing dark mitochondria. Numerous fibers in the stroma of cornea and iris were CGRP-positive. CGRP-positive staining was most intense within varicosities, containing mainly clear and incidentally granular vesicles and dark mitochondria, similar to the structures labelled with PHA-L. CGRP-positive varicosities packed with mainly clear and few granular vesicles also were demonstrated in fibers adjacent to the sphincter and dilator muscles of the iris. In the corneal epithelium, small terminals containing vesicles were CGRP-positive. Trigeminal nerve fibers innervating the rat cornea and iris contained numerous varicosities packed with vesicles. These areas are CGRP-positive, so it can be implied that CGRP is released from these varicosities as a response to triggering impulses. This agrees with the hypothesis that in addition to their afferent function, sensory fibers also exert an efferent modulating function.

Animals↗

PubMed1991

Ultrastructural identification of trigeminal nerve terminals in the pterygopalatine ganglion of rats: an anterograde tracing and immunohistochemical study.

Trigeminal nerve terminals in the rat pterygopalatine ganglion (PPG) were ultrastructurally identified using anterograde tracing with Phaseolus vulgaris-leucoagglutinin (PHA-L). Electron microscopic immunohistochemistry was used to demonstrate the presence of substance P (SP) and calcitonin gene-related peptide (CGRP) in nerve terminals of the PPG. Adjacent to the rostral part of the PPG an additional minor area was described. Perikarya in this minor rostral part were more spherical and had irregular outlines. Ultrastructurally, the glial enwrapment of the nerve terminals seemed to be more loosely arranged in comparison to that in the major rostral part of the PPG. With PHA-L, numerous labelled nerve fibres and terminals were found in all parts of the PPG. The ultrastructure of these terminals was uniform, many of them showing synaptic contacts. Numerous terminals in the PPG were SP-positive, whereas only a few were CGRP-positive. Fibres stained positive for both neuropeptides. The PPG is shown to be synaptically innervated by sensory fibres arising in the trigeminal ganglion, with the strong suggestion of SP and CGRP acting as neurotransmitters. A modulatory interaction between the autonomic and sensory system, resembling an axon reflex mechanism in the peripheral nervous system is endorsed.

Animals↗

PubMed1989

A written test as an alternative to performance testing.

Performance tests are logistically complex and time consuming. To reach adequate reliability long tests are imperative. Additionally, they are very difficult to adapt to the individual learning paths of students, which is necessary in problem-based learning. This study investigates a written alternative to performance-based tests. A Knowledge Test of Skills (KTS) was developed and administered to 380 subjects of various educational levels, including both first-year students and recently graduated doctors. By comparing KTS scores with scores on performance tests strong convergent validity was demonstrated. The KTS failed discriminant validity when compared with a general medical knowledge test. Also the identification of sub-tests discriminating between behavioural and cognitive aspects was not successful. This was due to the interdependence of the constructs measured. The KTS was able to demonstrate differences in ability level and showed subtle changes in response patterns over items, indicating construct validity. It was concluded that the KTS is a valid instrument for predicting performance scores and could very well be applied as supplementary information to performance testing. The relative ease of construction and efficiency makes the KTS a suitable substitute instrument for research purposes. The study also showed that in higher ability levels the concepts which were meant to be measured were highly related, giving evidence to the general factor theory of competence. However, it appeared that this general factor was originally non-existent in first-year students and that these competencies integrate as the educational process develops.

Clinical Competence↗

PubMed1989

Method for the detection of Shigella in foods.

A method for the detection of Shigella in foods was evaluated. The method consisted of selective enrichment at 37 degrees C in GN-broth supplemented with novobiocin (10 micrograms/ml) followed by subculture after 6 and 24 h incubation of 0.1 ml volumes to SS-agar with and without streptomycin (7.5 micrograms/ml). Test samples were contaminated by adding shigellae to 1:10 suspensions of foods (minced meat, fresh cut vegetables and cooked peeled shrimp) in the GN-broth with novobiocin. Shigella could be detected at a contamination level of 1 per 25 g in the presence of shrimp (in all 20 samples) and at 25 per 25 g in the presence of nearly all samples of fresh cut vegetables (in 13 out of 18 samples). Using this procedure Shigella could not be detected when the organism was present at a relatively high contamination level of 10(2) per 25 g in the presence of minced meat (with all 10 samples). However, the procedure described is an improvement on methods currently available for the detection of Shigella in foods.

Animals↗

PubMed1988

Influence of xylitol on growth, establishment, and cariogenicity of Streptococcus mutans in dental plaque of rats.

The influence of xylitol on glucose metabolism of Streptococcus mutans C67-1S was studied in vitro and in rats in vivo. In vitro there was an inhibition by xylitol of the growth rate and acid production of S. mutans C67-1S, but in vivo no effect on the initial growth rate could be demonstrated. In vivo there was a delay in the start of growth of S. mutans which resulted in a 10-day delay of establishment. The isolated xylitol-resistant mutant of C67-1S, S. mutans C67-1S XR, showed no difference in glucose metabolism in batch cultures. S. mutans C67-1S and S. mutans C67-1S XR were both used to study caries development in SPF Osborne Mendel rats. The rats were housed under programmed feeding conditions and were fed a glucose or a glucose-xylitol diet. In the case of S. mutans C67-1S, there was a remarkable inhibition of fissure caries lesions in the presence of xylitol compared to the glucose group. But also in the S. mutans C67-1S XR groups there were fewer lesions in the presence of xylitol. These results indicated that the anticariogenic properties of xylitol do not only depend on an inhibition of bacterial metabolism, but in part on other mechanisms.

Animals↗

PubMed1988

Microbiology and food hygiene in mass catering.

Serious consequences can arise from lack of hygiene in mass catering. The uncritical use of routine microbiological tests purporting to measure hygiene merely creates a false sense of security. The microbiological safety of food is achieved by as far as possible ensuring the absence of pathogenic microorganisms and by all means preventing their multiplication. The Hazard Analysis Critical Control Point concept is used to identify microbiologically vulnerable points in the food production process and to determine the most appropriate methods of control to be applied, usually such methods as improved handling techniques, monitoring of temperature and more intensive supervision. Microbiological testing is of value in the initial analysis, at appropriate intervals for verifying the effectiveness of control measures, and in demonstrating to food handlers the reality of the microbial risk if good hygienic standards are not maintained.

Accident Prevention↗

PubMed1988

The occurrence of salmonellae in kitchens of care institutions.

Sporadic cases of salmonellosis always by the same serotypes occurred in two different care institutions. In the first institution the cases had been caused by S. binza and S. eimsbuettel, in the second by S. mons and S. braenderup. The cases of salmonellosis prompted studies into the occurrence of these Salmonella serotypes in the kitchens of the relevant institutions, as well as into the occurrence of salmonellas in kitchens of care institutions in general. Using Moore's swabs the relevant Salmonella serotypes could be demonstrated in the kitchens of the institutions with sporadic cases of salmonellosis, while in kitchens of 15 other arbitrary chosen institutions Salmonella could not be detected at all. This demonstrated that the occurrence of sporadic cases of salmonellosis was related to the occurrence of salmonellas in the kitchens. Then investigations were started to establish the origin of the salmonellas. There was a mice plague in one institution. Mouse-dung was found positive for the relevant Salmonella serotype(s). Cases of salmonellas did not occur any more when the mice had been eradicated. It was concluded that the sporadic cases of salmonellosis in that institution were strongly associated with the presence of mice. In the other institution it appeared that disinfection was inadequate and that salmonellae were spread all over the kitchen environment during cleaning, leading to recontamination. After thorough disinfection and adaptation of cleaning and disinfection procedures sporadic cases of salmonellosis did not occur anymore. Results of these investigations demonstrated the important role of vermin and proper cleaning and disinfection in food hygiene. Moreover, the sporadic cases of salmonellosis came to light because gastro-enteritis was a reason for examination of faecal specimens of patients. This is not usual in many care institutions. However, in this way problems in hygiene can be traced, especially in the kitchen. For this reason it is recommended strongly to examine faecal specimens in cases of gastro-enteritis, even in sporadic cases.

Accident Prevention↗

PubMed1987

Public health aspects of microbial contaminants in food.

Food-borne diseases affect the health and welfare of hundred thousands of people and result in considerable economic loss. Salmonella and Campylobacter are by far the most important causes of food-borne illness. Raw foods of animal origin are the major sources of these pathogens. Mishandling of foods in kitchens contributes to food-borne disease outbreaks. More education is necessary. But because of the inevitable risk of recontamination of cooked foods in every kitchen, more emphasis should be placed on pathogen-free raising of food animals and good manufacturing practices during slaughter. This will minimise contamination of raw foods of animal origin, thus reducing the contamination pressure in the kitchen and more effectively controlling food-borne diseases.

Animals↗

PubMed1987

Fate of salmonellas and competing flora in meat sample enrichments in buffered peptone water and in Muller-Kauffmann's tetrathionate medium.

Studies have been carried out in which growth patterns of a Salmonella sp. and competing micro-organisms, especially other Enterobacteriaceae, were followed during pre-enrichment in buffered peptone water (BPw) and subsequent selective enrichment in tetrathionate broth (TBB). Pre-enrichment cultures were inoculated with minced meat and three reference samples containing nalidixic acid-resistant salmonellas. Irrespective of their initial numbers in BPw, Enterobacteriaceae increased to 10(8)/ml or more. During incubation in TBB at 43 degrees C, numbers of lactose-positive Enterobacteriaceae decreased in most enrichments which resulted in a positive salmonella isolation, but remained constant in the majority of those that did not. Levels of lactose-negative Enterobacteriaceae did not decrease in most salmonella-positive tests, but did so in half of the salmonella-negative ones. In the salmonella-positive tests the numbers of salmonellas had increased to 10(3)-10(7)/ml in BPw and after transfer to TBB slowly reached 10(4)/ml or more. In all cases the numbers of salmonellas exceeded those of the competing flora on brilliant green agar (BGA). In the salmonella-negative tests the numbers of salmonellas had increased less in BPw and decreased in most of the TBB enrichments. In none of these negative tests did the numbers of salmonellas exceed those of the competing flora on BGA. Escherichia coli dominated in most of the salmonella-negative tests. The results suggest more influence of lactose-positive than lactose-negative Enterobacteriaceae on the detection of salmonellas. The effect of competing microorganisms seems to depend not only upon their initial numbers, but also upon the types that can interact with salmonellas during selective enrichment.

Culture Media↗

PubMed1987

ICMSF methods study. XVII. An international comparative study of the direct plate and hydrophobic grid-membrane filter methods for enumeration of Escherichia coli in foods. International Commission on Microbiological Specifications for Foods.

Eight laboratories compared counts of Escherichia coli from naturally or artificially contaminated ground beef, other meats and poultry, vegetables, fish and shellfish, cheese, and diverse sources such as swabs, by the Anderson-Baird-Parker direct plate (DP) and a hydrophobic grid-membrane filter (HGMF) method. For five of the eight laboratories overall counts by HGMF were significantly low (51-83%) compared with those by DP. Counts by HGMF tended to be lower for naturally contaminated samples; several possible causes were investigated. In a subsidiary study, analyst variation in counting HGMF ranged from 0.8-7.3%, with little evidence of effects from counting positive versus negative grid cells or from the fullness of growth or staining intensity.

Bacteriological Techniques↗

PubMed1987

Collaborative study on the precision of the enumeration of Staphylococcus aureus in food.

In order to compare the precision of the enumeration of Staphylococcus aureus in food with egg yolk tellurite glycine pyruvate agar (ETGP-agar) and with rabbit plasma fibrinogen agar (RPF-agar), a collaborative study was carried out in which 23 laboratories participated. In this study each laboratory examined an identical series of 10 samples of ice cream, artificially contaminated with S. aureus and other Gram-positive cocci at roughly 10(4) per ml. The variations between the participating laboratories were smaller with RPF-agar than with ETGP-agar. The average values of the standard deviations were 0.10 and 0.13 log-units respectively. Laboratory specific errors were limited to 0.15 log-units with both media. For RPF-agar repeatability (r) was 0.26 (in log-units) and reproducibility (R) was 0.31 and for ETGP-agar r was 0.37 and R was 0.39. It is concluded that variations in S. aureus counts are limited and reproducibility is improved by using RPF-agar.

Culture Media↗