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Biomedical subjects

R G Stewart

Publications and source records attributed to R G Stewart.

At least 19 recordsLinked to original sources
PubMed1999

Sugar feeding by Culicoides mississippiensis (Diptera: Ceratopogonidae) on the yaupon holly, Ilex vomitoria.

Adult Culicoides mississippiensis Hoffman were collected from 5 flowering yaupon holly plants at sunrise, late morning, early afternoon, and sunset from 5 flowering yaupon holly plants during the entire flowering season (16 March-15 April 1995). Individual insects were tested for fructose by using the cold anthrone test. Prevalence of fructose in C. mississippiensis was 55.6% (427 of 768), with positivity for gravid females greater than for males. Fructose positive rates decreased in gravid females from morning to evening, whereas male rates were constant until evening, when they decreased. Both sugar feeding by gravid females and host-seeking by parous females were highest at sunset, followed by sunrise.

Animals↗
PubMed1998

Molecular epidemiology of an outbreak of Enterobacter cloacae in the neonatal intensive care unit of a provincial hospital in Gauteng, South Africa.

An outbreak of Enterobacter cloacae in the neonatal intensive care unit of a provincial hospital in Gauteng, South Africa, resulting in nine deaths was investigated. Macrorestriction analysis using pulsed-field gel electrophoresis revealed that three isolates of E. cloacae from blood cultures of patients, six from environmental sources, and one from the hands of a staff member belonged to the same genotypic cluster.

Cross Infection↗
PubMed1993

Avian keratoacanthoma (dermal squamous cell carcinoma) in broiler chicken carcasses.

Multiple lesions of dermal squamous cell carcinoma are found at a low frequency (0.04%) in the carcasses of young meat-type chickens at slaughter. For this study, affected carcasses (n = 308) were removed from the processing line, and lesions were characterized by size, distribution, and morphology. Carcasses were also sexed and examined for evidence of metastasis. Nodular (n = 297) and ulcerative (n = 1,707) lesions were counted and examined. Most lesions were present in the pectoral, dorsopelvic, and femoral feather tracts. Few lesions (n = 11) were found in wing tracts. Mean diameter was 5.4 mm for ulcerative lesions and 3.1 mm for nodular lesions. Histologic sections of ulcerative (n = 579) and nodular (n = 113) lesions were examined. Small nodular lesions originated from hyperplastic feather follicle epithelium. Nodules contained keratin-filled cysts lined by squamous epithelium that were associated with isolated islands and infiltrating cords of dermal keratinocytes. Loss of surface epithelium resulted in noduloulcerative and ulcerative lesions. Invasion of underlying skeletal muscle and evidence of visceral metastasis were not present, but invasion through elastic laminae and into the subcutis was present in 20.5% (134/654) of the lesions examined. The nodular lesions in these carcasses were morphologically similar to early nodular lesions previously described in live chickens as avian keratoacanthomas. A retrospective study compared selected production parameters and disease condemnations to the prevalence of squamous cell carcinoma in 665 flocks of broiler chickens. There was a positive correlation (P < 0.0001) with the occurrence of airsacculitis but a negative correlation with increased age and condemnations for leukosis (P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Corynebacterium group D2 urinary tract infection.

An unusual multiply resistant corynebacterium was isolated from the urine of a comatose patient. This organism was resistant to sulphafurazole, trimethoprim, nalidixic acid, cefazolin, nitrofurantoin, clindamycin, erythromycin, oxacillin, penicillin, gentamicin, amikacin, cinoxacin, ceftazidime and cefotaxime, but was susceptible to ciprofloxacin, ofloxacin, norfloxacin, vancomycin and fucidin. It was identified as the first reported isolate in South Africa of corynebacterium group D2, an organism recently implicated in alkaline-encrusted cystitis and urinary tract infection. We discuss the case history of the patient and review the literature.

Bacteriuria↗
PubMed1990

Transmission of exogenous genes into the chicken.

Injection of infectious non-replicating REV vector directly beneath the chicken blastoderm leads to infection of embryonic stem cells. Vector sequences are present in a variety of specialized tissues of embryos and mature birds derived from infected blastoderms. Breeding studies show that replication-defective REV vectors can transfer heritable, non-viral genetic information into the chicken germ line.

Animals↗
PubMed1985

The effect of aflatoxin on complement activity in broiler chickens.

Groups of broiler chickens were fed rations containing .625, 1.25, or 2.5 micrograms total aflatoxin/g of feed from one day to 42 days of age. Treatment groups were segregated according to sex and control groups were maintained. The chickens were bled at 14-day intervals, and serum was collected for assay of total complement (C) activity using a radial hemolytic procedure. No significant differences were found in C titers between males and females of the same age group. For the sexes combined, mean C titers of chickens fed aflatoxin were compared to mean titers of controls. For each age group, significant differences in C titers existed only between the control group and those chickens fed 2.5 micrograms/g aflatoxin. Complement is a major component of the humoral immune response and this study adds to the evidence that aflatoxin can be immunosuppressive to chickens.

Aflatoxins↗
PubMed1983

Work in progress: potential oral and intravenous paramagnetic NMR contrast agents.

The potential use of paramagnetic compounds as nuclear magnetic resonance (NMR) contrast agents was examined in vitro. The T1 relaxation times for serial dilutions of Cu2+, Cr3+, Fe3+, and Mn2+ ions in saline, gadolinium oxalate (a potential oral contrast agent) in suspension, and chromium EDTA (a potential intravenous contrast agent) in solution were determined. The effect on T1 of increasing the concentration of oxygen in solution was also examined. The relative magnitude of the decrease in T1 was, as expected, proportional to both the concentration of the paramagnetic substance and its effective magnetic moment. Thus NMR has the potential to detect differences in tissue oxygenation. By incorporating paramagnetic metal ions into insoluble compounds or stable complexes, toxicity can be dramatically reduced while maintaining a significant paramagnetic effect. Highly insoluble paramagnetic compounds or stable paramagnetic ion complexes can thus be utilized as effective NMR contrast agents with significantly diminished toxicity.

Administration, Oral↗
PubMed1980

Physiological effects of gentian violet on broiler chickens.

The effects of dietary gentian violet upon certain physiological parameters of broiler chickens were studied. Gentian violet exhibited no effect upon growth rates or feed conversion ratios at dietary levels of 16, 32, or 64 micrograms/g. In vitro intestinal absorption of methionine and glucose was also unaltered. Dietary gentian violet significantly increased hemoglobin concentration without an effect on packed cell volume. Furthermore, commercial gentian violet containing preparations, when incorporated into the diet, resulted in increased intestinal absorption of Fe59 but this increase was dependent upon type of inert carrier used. Dietary gentian violet alleviated some of the growth suppression caused by dietary aflatoxin; however, no effect was observed on plasma pigmentation. These data suggest that dietary gentian violet possesses effects other than those for which it has been traditionally employed.

Animals↗
PubMed1980

Hemolytic complement activity in broiler chickens and turkeys.

Broiler chickens and turkeys were tested for hemolytic complement (C) activity at 7 or 14 day intervals beginning at one day of age and ending at 42 days of age. The mean titers for chickens on days 1, 14, 28, and 42 were 1:14, 1:14, 1:22, and 1:33, respectively. The mean C titers for turkeys on days 1, 7, 14, 21, 28, and 42 were 1:4, 1:6, 1:9, 1:10, 1:19, and 1:25, respectively. Birds were segregated as to sex so hemolytic activities could be compared. There were no significant differences between sexes in C titers in broiler chickens at any of the ages tested. This was also true of turkeys, except at 42 days of age when the C titer of the hens was significantly higher than the toms. Complement titers increased with age in both broiler chickens and turkeys.

Animals↗
PubMed1977

Electroretinograms from broilers fed aflatoxin and T-2 toxin.

Thirty chicks were fed a commercial broiler grower ration from hatching to 26 days of age. Ten birds received aflatoxin (5 microgram/g. of ration) and 10 received T-2 toxin (5 microgram/g. of ration). The remaining 10 birds served as controls. After the 26 days, electroretinograms were recorded on a graphic recorder from the anesthetized birds. On the basis of wave amplitudes and durations from electroretinograms recorded in light and darkness and from different colored stimuli, no differences were detectable between treated birds and controls. Thus, the photochemistries of the retina were not sufficiently altered in this study to permit early detection of mycotoxicoses by electroretinograms.

Aflatoxins↗
PubMed1977

The effect of various antifungal agents on aflatoxin production and growth characteristics of Aspergillus parasiticus and Aspergillus flavus in liquid medium.

Various antifungal agents were added to a medium of 2% yeast extract-4% sucrose. Spores of a toxigenic strain of Aspergillus parasiticus were inoculated into the medium and incubated at 26 degrees C. for 10 days. Growth of the mold and aflatoxin formation were monitored every 48 hours during the experiment. Of the antifungal agents evaluated, propionic acid and crystal violet were the most effective compounds in retarding mold growth. Propionic acid was fungicidal at concentrations greater than 3.0 microgram/ml. whereas crystal violet exhibited a mold retarding activity at levels greater than 2,0 microgram/ml. Crystal violet retarded the growth rate of the mold during the initial stages of growth, however, this retardation was overcome after 10 days of incubation. Crystal violet also retarded aflatoxin production and sporulation of Aspergillus parasiticus; however, aflatoxin production was the most sensitive parameter. A survey involving 12 toxigenic isolates of A. parasiticus and A. flavus indicated that these species vary markedly in susceptibility to crystal violet.

Aflatoxins↗
PubMedDate not supplied

Spontaneous regression of "dermal squamous cell carcinoma" in young chickens.

Eight young chickens with lesions characteristic of those described as dermal squamous cell carcinoma were obtained before slaughter. Lesions were measured; representative lesions were biopsied and examined microscopically; and gross changes were monitored. Lesions appeared to originate as cystic, keratin-filled proliferations of the feather-follicle epithelium. These cysts progressed into raised, keratin-filled, and eventually ulcerated, nodules. Loss of the keratin core resulted in a shallow ulcer that became progressively flattened and regressed into a fibrous dermal scar. All lesions in the broilers regressed in 4 to 16 days (mean 14 days). Twenty roaster lesions completely regressed. For roasters, the mean time to regression was 20 days, with a range of 6 to 93 days. Although there was limited invasion of the dermis by atypical keratinocytes, the overall architecture and biological behavior were more consistent with a benign lesion.

Animals↗
PubMedDate not supplied

Alternative injection sites for a Pasteurella multocida bacterin.

Seven different injection sites for a Pasteurella multocida bacterin were evaluated by measuring the immune response and the local tissue reaction. Injection into the ventral surface of the tail or subcutaneously along the dorsal midline of the neck were the most suitable procedures. Ease of application was judged subjectively, and the tail site was found to be easier to inject accurately than the subcutaneous neck site. The tail injection site was found to be the best overall when immune response, tissue reaction, and ease of application were all considered.

Animals↗