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Biomedical subjects

R M Mitchell

Publications and source records attributed to R M Mitchell.

At least 19 recordsLinked to original sources
PubMed2007

Prevalence of antimicrobial resistance among Salmonella on midwest and northeast USA dairy farms.

The objective of this study was to determine the prevalence of antimicrobial resistance among Salmonella isolated from dairy herds in New York, Minnesota, Michigan, and Wisconsin, USA. Serogroup and antimicrobial susceptibility characteristics were determined for Salmonella from cattle and environmental samples collected during August 2000-October 2001 as part of a longitudinal study where 129 herds were visited at 2-month intervals. Salmonella isolates were tested (using a broth microdilution method) for susceptibility to amoxicillin/clavulanic acid, ampicillin, ceftiofur, ceftriaxone, cephalothin, chloramphenicol, ciprofloxacin, gentamicin, kanamycin, nalidixic acid, streptomycin, sulfamethoxazole, tetracycline, and trimethoprim/sulfamethoxazole. Of the 1506 isolates tested for minimum inhibitory concentrations to these 14 antimicrobial agents, 81.2% were pan-susceptible and for most herds (81.6%) the predominant antimicrobial resistance pattern was pan-susceptible. At least 1 Salmonella isolate resistant to 5 or more antimicrobial agents was found on 23.6% of herds. This resistance phenotype was most common among serogroups B and E1 and among samples from calves and farmer-designated sick cows. Resistant samples most frequently exhibited resistance to tetracycline, streptomycin, and/or ampicillin. No samples were resistant to ceftriaxone (though 13 were in the intermediate range), and very few samples were resistant to ciprofloxacin (n=1), nalidixic acid (n=5), or trimethoprim/sulfamethoxazole (n=7).

Animals↗
PubMed2006

Antimicrobial susceptibility of Salmonella from organic and conventional dairy farms.

The objective of this study was to compare antimicrobial susceptibility of Salmonella isolated from conventional and organic dairy farms in the Midwest and Northeast United States. Environmental and fecal samples were collected from organic (n = 26) and conventional (n = 69) farms in Michigan, Minnesota, New York, and Wisconsin every 2 mo from August 2000 to October 2001. Salmonella isolates (n = 1,243) were tested using a broth microdilution method for susceptibility to amoxicillin-clavulanic acid, ampicillin, ceftiofur, ceftriaxone, cephalothin, chloramphenicol, ciprofloxacin, gentamicin, kanamycin, nalidixic acid, streptomycin, sulfamethoxazole, tetracycline, and trimethoprim-sulfamethoxazole. Herd-level logistic regression and logistic proportional hazards multivariable models were used to examine the association between farm management type and susceptibility to antimicrobial agents. For most antimicrobial agents tested, susceptibility of Salmonella isolates was similar on organic and conventional herds when controlling for herd size and state. Conventional farms were more likely to have at least one Salmonella isolate resistant to streptomycin using logistic regression (odds ratio = 7.5; 95% confidence interval = 1.7-5.4). Conventional farms were more likely to have Salmonella isolates with greater resistance to streptomycin (odds ratio = 5.4; 95% confidence interval = 1.5-19.0) and sulfamethoxazole (odds ratio = 4.2; 95% confidence interval = 1.2-14.1) using logistic proportional hazards models. Although not statistically significant, conventional farms tended to be more likely to have at least one Salmonella isolate resistant to 5 or more antimicrobial agents when compared with organic farms.

Animals↗
PubMed2005

Endoscopic ultrasound and computer tomography are inaccurate methods of classifying cystic pancreatic lesions.

BACKGROUND: Despite advances in imaging modalities, preoperative diagnosis of pancreatic cystic lesions remains difficult. AIM: To assess the accuracy of endoscopic ultrasound and computer tomography to preoperatively distinguish benign from potentially malignant and malignant pancreatic cystic lesions. METHODS: Photograph series obtained from endoscopic ultrasound examinations of 66 patients with cystic pancreatic lesions were blindly reviewed by three endoscopic ultrasonographers. Forty-one of those 66 patients also underwent a computer tomography scan at our institution, which was blindly reviewed by a single radiologist. Computer tomography and endoscopic ultrasound classification into benign and malignant and potentially malignant pancreatic cystic lesions was correlated with the final diagnosis, which was established by surgical pathology (n = 43), diagnostic fine needle aspiration (n = 13) or follow-up imaging (n = 10). Interobserver agreement was measured using kappa statistics. RESULTS: Endoscopic ultrasound classification by the three examiners into benign versus malignant or potentially malignant cystic lesions was correct in 65-67%. Interobserver agreement was 50%. Kappa values for pairs of endoscopic ultrasound examiners were 0.16, 0.43 and 0.53. Computer tomography classification was correct in 71% and in agreement with the endoscopic ultrasound classification in 56-61% (kappa 0.12 to 0.27). CONCLUSIONS: Endoscopic ultrasound and computer tomography cannot accurately distinguish between benign pancreatic cystic lesions and malignant or potentially malignant ones. There is poor-to-modest interobserver agreement in classifying these lesions.

Adult↗
PubMed2004

Complications of pancreaticoduodenectomy after neoadjuvant chemoradiation in patients with and without preoperative biliary drainage.

BACKGROUND: It has been suggested that preoperative biliary drainage increases the risk of infectious complications of pancreaticoduodenectomy. AIMS: The aim of this study was to assess complications related to biliary stents/drains and postoperative morbidity in patients undergoing neoadjuvant chemoradiotherapy for periampullary cancer. PATIENTS: One hundred and eighty-four patients with periampullary neoplasms were prospectively selected for neoadjuvant external beam radiation therapy and 5-fluorouracil-based chemotherapy between 1995 and 2002. METHODS: The data were retrospectively completed and analysed with respect to biliary drainage, efficacy and complications of endoscopic biliary stents and postoperative morbidity. Patients who had undergone a surgical biliary bypass were excluded. RESULTS: Data were completed in 168 patients. One hundred and nineteen patients were treated with endoscopic biliary stents, 18 patients had a percutaneous biliary drain and 31 patients did not require biliary drainage. Hospitalisation for stent-related complications was necessary in 15% of the patients with endoscopic biliary stents. Seventy-two patients underwent pancreaticoduodenectomy. There was no significant difference in the rate of wound infections, intra-abdominal abscesses and overall complications between the groups with and without preoperative biliary drainage. CONCLUSIONS: Postoperative infectious complications are common in patients both with and without preoperative biliary drainage. A statistically significant difference in complication rates was not observed between these groups.

Adult↗
PubMed2004

Yield of endoscopic ultrasound-guided fine-needle aspiration of bile duct lesions.

BACKGROUND AND STUDY AIMS: It is still difficult to differentiate reliably between benign and malignant biliary tract lesions. Endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) has added to the diagnostic power of EUS for other gastrointestinal tumors. A retrospective analysis of experience with FNA sampling of bile duct lesions was therefore carried out. PATIENTS AND METHODS: All EUS-FNA procedures for bile duct masses or strictures were analyzed at our tertiary referral center from May 2000 through October 2002. Data for EUS findings, the results of EUS-FNA, and tissue sampling at surgery were included. EUS-FNA procedures were carried out using a 22-gauge needle. An experienced cytopathologist was present during FNA in all but three cases. Clinical follow-up details were recorded when available for patients in whom a suitable diagnostic gold standard was not available for comparison. RESULTS: A total of 35 patients underwent EUS-FNA of bile duct lesions during the study period. There were no complications. Data for EUS-FNA of bile duct masses or strictures and tissue obtained at surgery were available for 23 patients. If positive cytology at surgical pathology is taken as the gold standard, EUS-FNA has a diagnostic yield for cancer of 100 % (if atypia/inconclusive findings in the FNA sample are regarded as benign). Eleven patients had a definite malignancy on surgical pathology. Of these 11 patients, five had a finding of malignancy on EUS-FNA, giving a sensitivity of 45 % (if FNA cytology reported as atypia/inconclusive is regarded as benign). Twelve patients had findings of no malignancy from tissue obtained at surgery. Of these 12 patients, nine had benign pathology and three had atypia/inconclusive findings in the EUS-FNA sample (specificity of 100 % if atypia/inconclusive findings are considered benign). A further 12 patients did not have surgical specimens for comparison with EUS-FNA results. Four patients had definite findings of malignancy on EUS-FNA alone, and one patient had FNA findings suspicious for malignancy. Seven patients had negative or equivocal EUS-FNA results. These 12 patients are described but excluded from further analysis, as a gold standard was not available for comparison. However, clinical follow-up data were available for eight of these 12 patients, and in each case the follow-up findings were compatible with previous benign or malignant EUS-FNA findings. CONCLUSIONS: The practice of EUS-FNA has improved the diagnostic yield of EUS. These results suggest that it is a safe and useful procedure for investigating biliary masses or strictures that have hitherto caused considerable diagnostic confusion, especially in patients with negative brush cytology findings. The possibility of false-negative findings remains, but core biopsy needles may improve the situation. The results of further studies are awaited.

Aged↗
PubMed2001

Flexible sigmoidoscopy and the changing distribution of colorectal cancer: implications for screening.

BACKGROUND AND AIMS: There has been a significant proximal shift in the distribution of colorectal cancer (CRC) in Northern Ireland over recent decades. The aim of this study was to investigate the potential implications of this proximal shift in CRC distribution on the efficacy of flexible sigmoidoscopy (FS) as a screening tool. PATIENTS AND METHODS: The site distribution of 5153 CRCs was available from the Northern Ireland Colorectal Cancer Register for the period 1990-1997. Similar data on 1241 CRCs between 1976 and 1978 were available from a previous study. Data on the site reached by FS were obtained from a prospectively collected endoscopy database at one of Northern Ireland's main teaching hospitals for the period 1993-1998. RESULTS: There was a significant proximal shift in CRC distribution between the two periods (23.5% proximal to the splenic flexure between 1976 and 1978 v 36.7% between 1990 and 1997; p<0.001). The descending colon was visualised during 74.4% of FS examinations. By combining the observed extent of FS examination with CRC site distribution, it was calculated that FS could have visualised 68.8% of CRCs between 1976 and 1978 but only 56.0% between 1990 and 1997. Extrapolating these data to a Northern Ireland screening programme involving FS and faecal occult blood testing suggests that significantly more CRCs could have been detected between 1976 and 1978 than between 1990 and 1997 (51.7% v 48.2%, respectively; p=0.03). CONCLUSIONS: This study confirms the previously documented left to right shift in CRC distribution in Northern Ireland and demonstrates that if this shift continues, FS will become less successful as a screening tool than is currently predicted.

Colorectal Neoplasms↗
PubMed1998

The influence of pregnancy on human immunodeficiency virus type 1 infection: antepartum and postpartum changes in human immunodeficiency virus type 1 viral load.

OBJECTIVE: Our objective was to examine the influence of pregnancy on human immunodeficiency virus type 1 viral load by measuring human immunodeficiency virus type 1 ribonucleic acid levels during pregnancy and post partum. STUDY DESIGN: One or more plasma or serum specimens obtained before and during the third trimester, and at 2, 12, and 24 months post partum were available for 160 human immunodeficiency virus type 1-seropositive women enrolled in the Mothers and Infants Cohort Study between January 1986 and January 1991. All specimens were frozen and stored at -70 degrees C until analyzed in batch for human immunodeficiency virus type 1 ribonucleic acid by polymerase chain reaction. A multivariate longitudinal random effects model was developed to examine changes in human immunodeficiency virus type 1 ribonucleic acid levels over time. RESULTS: Overall, human immunodeficiency virus type 1 ribonucleic acid levels rose significantly during the study period, particularly during the second year post partum (mean, 0.09 log per year; 95% confidence interval, 0.03 to 0.15 logs per year; p = 0.005). However, the mean slope during pregnancy was not significantly different from zero (p = 0.65). CONCLUSION: Pregnancy had little immediate effect on human immunodeficiency virus type 1 viral load in most human immunodeficiency virus type 1-seropositive women.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Influence of other maternal variables on the relationship between maternal virus load and mother-to-infant transmission of human immunodeficiency virus type 1.

To assess the relationship between maternal human immunodeficiency virus (HIV) type 1 RNA level, other important covariates, and mother-to-infant (vertical) transmission of HIV-1, third trimester repository specimens from 160 HIV-1-seropositive women enrolled in the Mothers and Infants Cohort Study between 1986 and 1991 were assayed in batch for HIV-1 RNA. A significant association between peripheral blood HIV-1 RNA level and vertical transmission remained after controlling for CD4 cell level, duration of ruptured membranes, "hard" drug (cocaine and heroin) use, and frequency of sexual activity during pregnancy. However, the association was attenuated among women with advanced HIV infection and those with a high frequency of sexual activity during pregnancy. In these settings, interventions that target risk factors other than virus load may be particularly important for preventing vertical transmission of HIV-1.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Comparative evaluation of treated bovine pericardium as a xenograft for hernia repair.

Two forms of bovine pericardium (BPC) were assessed as hernia repair materials: non-cross-linked (lyophilized) and cross-linked through treatment with glutaraldehyde (GA). These were compared with polypropylene mesh (Marlex) in a rabbit model. Over 52 wk implantation, the GA BPC grafts developed a strong, stable, fibrous tissue replacement with good incorporation into the abdominal muscle wall. The lyophilized BPC grafts were substantially resorbed within 12 wk of implantation, however the thin, fibrous replacement tissue was inadequate for abdominal wall support. Marlex grafts provided sufficient abdominal support, however these grafts were associated with extensive adhesion formation and, in this model, fat deposition around the perimeter of the graft. Control (ungrafted) rabbit abdominal muscle in the transverse orientation had an ultimate tensile load (UTL) of 11.4 +/- 5.1 N (x +/- s.d.) and a strain at UTL of 35 +/- 12% (n = 169). At 52 weeks the UTL of the repair sites was 7.3 +/- 4.5 N (n = 6), 5.1 +/- 3.5 N (n = 6) and 5.6 +/- 2.7 N (n = 6) for GA BPC, lypophilized BPC and Marlex grafts, respectively.

Animals↗
PubMed1986

Radionuclide uptake by trees at a radwaste pond in Washington State.

This paper presents work conducted in the summer of 1980 by Rockwell Hanford Operations, Hanford, WA, in support of a proposed effort to decommission and decontaminate a Hanford radwaste pond (216-U-10 Pond). The radionuclide values presented here are in addition to the U-Pond work that was recently published (La83) and are below any levels of environmental concern and within state and federal guidelines. U-Pond was constructed in 1944 for the surface disposal of industrial waste waters from nuclear separation processes and is one of the longest used aquatic, low-level, radioactive waste-disposal sites in the world. Tree leaf/twig, root, core and soil samples were collected and analyzed for 137Cs, 90Sr and 239Pu/240Pu. Strontium-90 was more readily taken up by trees than 137Cs or 239Pu/240Pu. Soil concentration values for 137Cs and 239Pu/240Pu were significantly greater (p less than or equal to 0.05) than all tree component parts. Radionuclide concentration ratios were higher for 90Sr (0.01-1355.0) than for 137Cs and 239Pu/240Pu for all tree components examined. Concentration ratios for 239Pu/240Pu ranged from 10(-6) to 10(-2) and are comparable to other studies conducted at the U.S. Department of Energy's Oak Ridge and Savannah River laboratories. These data represent the first quantitative information with respect to radionuclide uptake by trees on the Hanford Site.

Cesium Radioisotopes↗
PubMed1985

On the site of action of the anti-adrenal steroidogenic effect of cyproterone acetate.

Cyproterone acetate (CA) inhibited 1-24 ACTH (50 ng/l)-stimulated cortisol production by dispersed guinea-pig adrenal cells in a dose-related manner. Inhibition occurred over the range 10(-6) to 5 X 10(-5) moles/l. The concentration of drug which induced 50% inhibition was 4.6 X 10(-6) moles/l. The sites of action of this anti-steroidogenic effect have been established. Dispersed adrenal cells were challenged with the cortisol precursor steroids (all at 10(-5) moles/l) pregnenolone (Pe), 17 alpha hydroxypregnenolone (17-OH Pe), 17 alpha-hydroxyprogesterone (17-Po), and 11 deoxycortisol or 1-24 ACTH (100 ng/1) in the absence and presence of increasing concentrations of CA (10(-5) to 10(-4) moles/l). In the absence of drug, the steroid precursors or ACTH provoked cortisol secretion greater than 10-fold that secreted by cells incubated in their absence. ACTH-stimulated cortisol secretion was inhibited greater than 68% at concentrations of CA greater than 10(-5) moles/l. CA (10(-5) moles/l) had no significant effect on steroid-stimulated cortisol production when the delta 4, 3 ketosteroids 17-OH Po and 11-deoxycortisol were used, but depressed secretion by greater than 61% (P less than 0.001) when the delta 5 3 beta hydroxysteroids (Pe, 17-OH Pe) were employed. Increasing CA concentrations to 10(-4) moles/l had little effect on cortisol secretion provoked by 11-deoxycortisol, but significantly (P less than 0.05) depressed cortisol secretion stimulated by 17-OH Po. These results suggest that the major site of action of CA is delta 5, 3 beta hydroxysteroid dehydrogenase (3 beta-HSD) with a secondary effect on 21-hydroxylase activity. To confirm these findings cortisol secretion provoked by 17, 21, dihydroxypregnenolone (17, 21 diOH Pe) and 21 deoxycortisol (21-DOC) was measured in the absence and presence of increasing concentrations of CA. At the lowest concentration of CA (5 X 10(-6) moles/l), cortisol secretion provoked by 17, 21 diOH Pe was inhibited by 28% (P less than 0.01) whereas secretion provoked by 21-DOC was not significantly affected. At the highest concentration of CA (10(-4) moles/l), the relative inhibition was 80% for 17, 21 diOH Pe and 38% for 21-DOC. We conclude that cyproterone acetate inhibits adrenal steroidogenesis at both 3 beta-HSD and 21-hydroxylase, the degree of inhibition being more pronounced at 3 beta-HSD.

3-Hydroxysteroid Dehydrogenases↗
PubMed1985

Anatomical localization of atherosclerotic lesions using the pulse volume recorder.

The pulse volume recorder has been used in studying 62 limbs to assess its accuracy in localization of arteriosclerotic lesions of the lower limbs, realizing the limitations of clinical examination and simple pressure measurements. Its advantages over simple pressure measurements are illustrated. It was shown to be most accurate in locating isolated stenoses. The technique helps differentiate aorto-iliac from high superficial femoral artery obstruction. It can be used when severe medial sclerosis is present and is very helpful when distal pulses cannot be detected for technical reasons.

Adult↗
PubMed1979

DNA organization of Methanobacterium thermoautotrophicum.

The organism Methanobacterium thermoautotrophicum, an archaebacterium, is envolutionarily very distant from both traditional prokaryotes and eukaryotes. Its genome (DNA) has physical characteristics typical of most prokaryotes except that it is quite small (about 10(9) daltons, less than half the size of the genome of Escherichia coli) and contains a significant amount (6 percent) DNA which renatures extremely rapidly.

Base Sequence↗