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Biomedical subjects

M C Roberts

Publications and source records attributed to M C Roberts.

At least 19 recordsLinked to original sources
PubMed2006

Antibiotic resistance genes in multidrug-resistant Enterococcus spp. and Streptococcus spp. recovered from the indoor air of a large-scale swine-feeding operation.

AIMS: In this study, multidrug-resistant bacteria previously recovered from the indoor air of a large-scale swine-feeding operation were tested for the presence of five macrolide, lincosamide and streptogramin (MLS) resistance genes and five tetracycline (tet) resistance genes. METHODS AND RESULTS: Enterococcus spp. (n = 16) and Streptococcus spp. (n =16) were analysed using DNA-DNA hybridization, polymerase chain reaction (PCR) and oligoprobing of PCR products. All isolates carried multiple MLS resistance genes, while 50% of the Enterococcus spp. and 44% of the Streptococcus spp. also carried multiple tet resistance genes. All Enterococcus spp. carried erm(A) and erm(B), 69% carried erm(F), 44% carried mef(A), 75% carried tet(M), 69% carried tet(L) and 19% carried tet(K). All Streptococcus spp. carried erm(B), 94% carried erm(F), 75% carried erm(A), 38% carried mef(A), 50% carried tet(M), 81% carried tet(L) and 13% carried tet(K). CONCLUSIONS: Multidrug resistance among airborne bacteria recovered from a swine operation is encoded by multiple MLS and tet resistance genes. These are the first data regarding resistance gene carriage among airborne bacteria from swine-feeding operations. SIGNIFICANCE AND IMPACT OF THE STUDY: The high prevalence of multiple resistance genes reported here suggests that airborne Gram-positive bacteria from swine operations may be important contributors to environmental reservoirs of resistance genes.

Air Microbiology↗
PubMed2006

Mutans streptococci dose response to xylitol chewing gum.

Xylitol is promoted in caries-preventive strategies, yet its effective dose range is unclear. This study determined the dose-response of mutans streptococci in plaque and unstimulated saliva to xylitol gum. Participants (n = 132) were randomized: controls (G1) (sorbitol/maltitol), or combinations giving xylitol 3.44 g/day (G2), 6.88 g/day (G3), or 10.32 g/day (G4). Groups chewed 3 pellets/4 times/d. Samples were taken at baseline, 5 wks, and 6 mos, and were cultured on modified Mitis Salivarius agar for mutans streptococci and on blood agar for total culturable flora. At 5 wks, mutans streptococci levels in plaque were 10x lower than baseline in G3 and G4 (P = 0.007/0.003). There were no differences in saliva. At 6 mos, mutans streptococci in plaque for G3 and G4 remained 10x lower than baseline (P = 0.007/0.04). Saliva for G3 and G4 was lower than baseline by 8 to 9x (P = 0.011/0.038). Xylitol at 6.44 g/day and 10.32 g/day reduces mutans streptococci in plaque at 5 wks, and in plaque and unstimulated saliva at 6 mos. A plateau effect is suggested between 6.44 g and 10.32 g xylitol/day.

Adolescent↗
PubMed2005

The use of ribotyping and antibiotic resistance patterns for identification of host sources of Escherichia coli strains.

AIMS: To compare antibiotic resistance and ribotyping patterns ability to identify triplicate isolates sent from a group of 40 Escherichia coli taken from seven host sources. METHODS AND RESULTS: Of the 120 isolates, 22 isolates were resistant to ampicillin, streptomycin, tetracycline and trimethoprim and 98 isolates were susceptible. Antibiotic patterns identified 33 of the triplicates and three of the six groups had isolates from multiple hosts. Ribotyping divided the isolates into 27 ribotype groups with all triplicates grouped into the same ribotype group with one host per group. CONCLUSIONS: Antibiotic susceptibility pattern placed 98 of the isolates in a single group with 50% of the antibiotic susceptibility pattern groups containing multiple host species. Ribotyping groups were host specific with each host having one to seven ribotype groups. SIGNIFICANCE AND IMPACT OF THE STUDY: Antibiotic susceptibility pattern groups have been used for environmental source identification and faecal pollution tracking, however these groups do not always distinguish between host species. Stability of the markers is a potential concern and this system can only be used if antibiotic resistance levels are high in the isolates studied. All isolates have a ribotype group which was stable and like other molecular methods has advantages over antibiotic susceptibility pattern groups which uses a phenotypic method.

Animals↗
PubMed2004

The mef(A) gene predominates among seven macrolide resistance genes identified in gram-negative strains representing 13 genera, isolated from healthy Portuguese children.

Of the 176 randomly selected, commensal, gram-negative bacteria isolated from healthy children with low exposure to antibiotics, 138 (78%) carried one or more of the seven macrolide resistance genes tested in this study. These isolates included 79 (91%) isolates from the oral cavity and 59 (66%) isolates from urine samples. The mef(A) gene, coding for an efflux protein, was found in 73 isolates (41%) and was the most frequently carried gene. The mef(A) gene could be transferred from the donors into a gram-positive E. faecalis recipient and a gram-negative Escherichia coli recipient. The erm(B) gene transferred and was maintained in the E. coli transconjugants but was found in 0 to 100% of the E. faecalis transconjugants tested, while the other five genes could be transferred only into the E. coli recipient. The individual macrolide resistance genes were identified in 3 to 12 new genera. Eight (10%) of the oral isolates and 30 (34%) of the urine isolates for which the MICs were 2 to >500 microg of erythromycin per ml did not hybridize with any of the seven genes and may carry novel macrolide resistance genes.

Bacterial Proteins↗
PubMed2002

Persistence of oral Candida albicans carriage in healthy Portuguese schoolchildren followed for 3 years.

Little is known about carriage of Candida albicans, the predominant pathogenic yeast in oral infection, in children. We cultured buccal mucosal and gingival swabs from 150 Portuguese children to investigate the prevalence of C. albicans at baseline (before dental treatment), post-treatment, and 12, 24, and 36 months post-baseline. The children, aged 8 to 11 years at baseline, had no systemic disease or clinical symptoms of oral candidiasis. At each successive visit, respectively, 47, 32, 21, 27, and 28% of children were C. albicans positive, resulting in an almost 50% reduction in prevalence from baseline to post-treatment (P < 0.0005). Children who carried C. albicans at one visit had 3 to 20 times greater odds of carrying C. albicans at another visit. C. albicans was cultured from 12 children at all time-points and from 10 children at four time-points. Children with oral C. albicans frequently maintained carriage over time, even with regular dental care.

Age Factors↗
PubMed2001

Managed mental health care: attitudes and ethical beliefs of child and pediatric psychologists.

OBJECTIVE: To examine child and pediatric psychologists' ethical beliefs and attitudes toward managed mental health care. METHODS: In a survey mailed in spring 1997, 252 child and pediatric psychologists responded to three vignettes depicting ethical dilemmas related to working with managed mental health care (confidentiality, restriction of services, misdiagnosis). Data were collected about psychologists' ethical choices and reasons given for choices, attitudes toward managed care, the extent to which managed care affected ethical decision making, and level of managed care involvement. RESULTS: Differences were found in choices made for the ethical dilemmas in regard to what participants thought they should do, would do, and actually did do. Overall, participants endorsed negative attitudes toward managed care. Participants reported that managed care somewhat affected their ethical decision making for the vignettes. Level of managed care involvement was not related to ethical decision making or attitudes toward managed care. CONCLUSIONS: The findings suggest areas for examination as new ethical standards are created for work in managed care environments.

Adult↗
PubMed2001

Autosomal dominant canine malignant hyperthermia is caused by a mutation in the gene encoding the skeletal muscle calcium release channel (RYR1).

BACKGROUND: Malignant hyperthermia (MH) is an inherited disorder of skeletal muscle characterized by hypercarbia, rhabdomyolysis, generalized skeletal muscle contracture, cardiac dysrhythmia, and renal failure, that develops on exposure to succinylcholine or volatile anesthetic agents. All swine and up to 50% of human MH events are thought to be associated with mutations in the calcium release channel of the sarcoplasmic reticulum, also known as the ryanodine receptor (RYR1). Events resembling MH have been reported in other species, but none have undergone genetic investigation to date. METHODS: To determine the molecular basis of canine MH, a breeding colony was established with a male, mixed-breed, MH-susceptible (MHS) dog that survived an in vivo halothane-succinylcholine challenge. He was mated to three unaffected females to produce four litters and back-crossed to an affected daughter to produce one litter. One of his MHS sons was mated to an unaffected female to produce an additional litter. Forty-seven dogs were phenotyped with an in vitro contracture test and diagnosed as MHS or MH normal based on the North American in vitro contracture test protocol. Nine microsatellite markers in the vicinity of RYR1 on canine chromosome 1 (CFA01) were tested for linkage to the MHS phenotype. Mutational analysis in two MHS and two MH-normal dogs was performed with direct sequencing of polymerase chain reaction products and of cloned fragments that represent frequently mutated human RYR1 regions. A restriction fragment length polymorphism was chosen to detect the candidate mutation in the pedigree at large. RESULTS: Pedigree inspection revealed that MHS in this colony is transmitted as an autosomal dominant trait. FH2294, the marker closest to RYR1, is linked to MHS at a theta = 0.03 with a LOD score of 9.24. A T1640C mutation gives rise to an alanine for valine substitution of amino acid 547 in the RYR1 protein, generating a maximum LOD score of 12.29 at theta = 0.00. All dogs diagnosed as MHS by in vitro contracture test were heterozygous for the mutation, and all MH-normal dogs were homozygous for the T1640 allele. CONCLUSIONS: These results indicate that autosomal dominant canine MH is caused by a mutation in the gene encoding the skeletal muscle calcium release channel and that the MHS trait in this pedigree of mixed-breed dogs is in perfect cosegregation with the RYR1 V547A mutation.

Amino Acid Sequence↗
PubMed2001

Amino acid repetitions in the dihydropteroate synthase of Streptococcus pneumoniae lead to sulfonamide resistance with limited effects on substrate K(m).

Sulfonamide resistance in Streptococcus pneumoniae is due to changes in the chromosomal folP (sulA) gene coding for dihydropteroate synthase (DHPS). The first reported laboratory-selected sulfonamide-resistant S. pneumoniae isolate had a 6-bp repetition, the sul-d mutation, leading to a repetition of the amino acids Ile(66) and Glu(67) in the gene product DHPS. More recently, clinical isolates showing this and other repetitions have been reported. WA-5, a clinical isolate from Washington State, contains a 6-bp repetition in the folP gene, identical to the sul-d mutation. The repetition was deleted by site-directed mutagenesis. Enzyme kinetic measurements showed that the deletion was associated with a 35-fold difference in K(i) for sulfathiazole but changed the K(m) for p-aminobenzoic acid only 2.5-fold and did not significantly change the K(m) for 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine pyrophosphate. The enzyme characteristics of the deletion variant were identical to those of DHPS from a sulfonamide-susceptible strain. DHPS from clinical isolates with repetitions of Ser(61) had very similar enzyme characteristics to the DHPS from WA-5. The results confirm that the repetitions are sufficient for development of a resistant enzyme and suggest that the fitness cost to the organism of developing resistance may be very low.

Adolescent↗
PubMed2001

Pharmacokinetics and adverse effects of butorphanol administered by single intravenous injection or continuous intravenous infusion in horses.

OBJECTIVE: To determine an infusion rate of butorphanol tartrate in horses that would maintain therapeutic plasma drug concentrations while minimizing development of adverse behavioral and gastrointestinal tract effects. ANIMALS: 10 healthy adult horses. PROCEDURE: Plasma butorphanol concentrations were determined by use of high-performance liquid chromatography following administration of butorphanol by single IV injection (0.1 to 0.13 mg/kg of body weight) or continuous IV infusion (loading dose, 17.8 microg/kg; infusion dosage, 23.7 microg/kg/h for 24 hours). Pharmacokinetic variables were calculated, and changes in physical examination data, gastrointestinal tract transit time, and behavior were determined over time. RESULTS: A single IV injection of butorphanol was associated with adverse behavioral and gastrointestinal tract effects including ataxia, decreased borborygmi, and decreased defecation. Elimination half-life of butorphanol was brief (44.37 minutes). Adverse gastrointestinal tract effects were less apparent during continuous 24-hour infusion of butorphanol at a dosage that resulted in a mean plasma concentration of 29 ng/ml, compared with effects after a single IV injection. No adverse behavioral effects were observed during or after continuous infusion. CONCLUSIONS AND CLINICAL RELEVANCE: Continuous IV infusion of butorphanol for 24 hours maintained plasma butorphanol concentrations within a range associated with analgesia. Adverse behavioral and gastrointestinal tract effects were minimized during infusion, compared with a single injection of butorphanol. Continuous infusion of butorphanol may be a useful treatment to induce analgesia in horses.

Analgesics, Opioid↗
PubMed2001

Intoxication, criminal offences and suicide attempts in a group of South African problem drinkers.

BACKGROUND: Incidence rates of crime and alcohol abuse in South Africa are unacceptably high. Research suggests a relationship between alcohol and both crime and suicide. This study aims to add to the information base on this topic in South Africa. METHODS: This is a cross-sectional record study of criminal offences and suicide attempts in 269 admissions to an alcohol rehabilitation unit in the Western Cape. Types of criminal offences and suicide attempts are described. Relationships are sought between crime, violent crime and suicide attempts on the one hand, and demographic and alcohol-related variables on the other. RESULTS: One hundred and four subjects (39%) had criminal convictions, the majority of which were committed while the subjects were intoxicated. The commonest alcohol-related crimes were driving-related (17% of subjects) and crimes of violence (15%). Male gender, younger age at initiation of drinking, and earlier onset of problem drinking were significantly associated with criminal behaviour. Violent crime was associated with earlier onset of initial, regular and problem drinking, and maternal alcohol abuse. Suicide attempts (24% of subjects) were associated with female gender, white racial group, not being in a marital relationship, younger current age and early age of problem drinking. CONCLUSIONS: There was an association between intoxication and both violent crime and suicide attempts. The importance of population studies and the need for intervention programmes aimed at teenagers who are drinking, are emphasised.

Adult↗
PubMed2000

Changes in the lipophilicity of the surfaces of Meloidogyne incognita and Haemonchus contortus during exposure to host signals.

The surfaces of plant and animal parasitic nematodes share certain lipids, which seem to be important in the infection process. The surfaces of 2 parasitic nematodes, Meloidogyne incognita and Haemonchus contortus, were activated by different pH buffers to allow the insertion of different fluorescent probes. The lipid analogue PKH26 and the surface charge indicator, cationized ferritin, were used as probes with these nematodes but labelled only the retaining 2nd-stage moulted cuticle of H. contortus 3rd-stage larvae (L3). Shedding of the second moult of H. contortus L3 was also visualized with PKH26 and cationized ferritin. The fluorescent anionic lipid probe 5-N-(octadecanoyl)-aminofluorescein (AF18) was inserted into the epicuticle layer of M. incognita 2nd-stage juveniles (J2) and H. contortus L3, and also of the second moult of H. contortus L3. Incubation with tomato root diffusate caused modifications of the M. incognita surface allowing the insertion of AF18. Fluorescence with AF18 was significantly decreased after treating M. incognita J2 with amiloride, a potent blocker of hydrogen and sodium (H+/Na+) antiporter. No surface fluidity was observed in M. incognita J2 and H. contortus L3 pre-treated with alkaline buffer when the lipid analogue AF18 was used in fluorescence recovery after photobleaching experiments. The significance of these findings to host infection processes is discussed.

Amiloride↗
PubMed2000

Mothers' and children's perceptions of medication for children with attention-deficit hyperactivity disorder.

This study assessed the perceptions about medication held by mothers and children with ADHD. Thirty-one mother-child dyads completed questionnaires assessing their knowledge and perceptions of stimulant medication and their level of perceived side effects associated with taking medication for ADHD. Mothers tended to view their children's medication as more beneficial than did their children. Mothers also demonstrated significantly more knowledge about their children's medication. Implications are drawn for research and clinical education of children and parents about medication for ADHD.

Adolescent↗
PubMed2000

Serum antibody titers to Bacteroides forsythus in elderly subjects with gingivitis or periodontitis.

BACKGROUND: The risks for periodontal disease appear to increase with age. STUDY PURPOSE: To determine associations between clinical findings, the presence of specific bacteria in periodontal pockets, and serum antibody titers. 10 older subjects (mean age=73.0 years SD+/-4.9) with confirmed gingivitis only (gingivitis group) and 10 subjects with periodontitis (mean age: 76.1 years, SD+/-10.4) (periodontitis group) were studied. RESULTS: The mean group differences for probing depth and clinical attachment levels were 4.1 mm and 5.6 mm, respectively, and were significantly different (p<0.001). Both groups had high plaque scores (>60% surfaces with plaque). DNA probes demonstrated that B. forsythus was present in 8/10 samples from the periodontitis group and in 7/10 samples from the gingivitis group. The B. forsythus isolates studied were found in four of the subjects with periodontitis and from 2 of the subjects with gingivitis. Serum antibody titers to 6 ribotypes of B. forsythus were studied. Western blots, gradient gels, and pulsed field gel electrophoresis concurrently demonstrated that the B. forsythus isolates were genotypically, and phenotypically unique for each subject. Antibody titers to two selected B. forsythus isolates were significantly higher in the periodontitis group (p<0.01, Mann-Whitney test). The study confirmed that antibody serum titers to the six different ribotypes of B. forsythus varied greatly between older individuals with gingivitis or periodontitis. Not all strains of B. forsythus elicited higher titers in periodontitis affected subjects. CONCLUSIONS: The results of the present study suggest genotype variation of B. forsythus that is unique to the individual and that serotype variation can be expected. It is possible that B. forsythus under specific host conditions can modulate surface antigen factors to evade the host immune response.

Age Factors↗
PubMed2000

Secretion of IL-12 by murine macrophages activated by immunoglobulin receptor-mediated internalization of the surface coat of Trichinella spiralis larvae.

Trichinella spiralis larvae incubated with a rabbit antiserum raised against the larval surface coat bound murine macrophages to the parasite surface. Cell binding was not observed without the antisurface coat serum, or with incubation of larvae in normal rabbit serum, or with antibodies to keyhole limpet haemocyanin which identify a cryptic T. spiralis larval antigen. Cell adherence to the larval surface was lost by treatment of the cells with the lysosomotropic drug primaquine, implicating a receptor-mediated mechanism. Cells adhering to the parasite surface internalized parasite surface coat material, which was subsequently concentrated into endosomes. Culture supernatants from these cells contained enhanced levels of IL-12. Thus, the initial Th1 response to T. spiralis infection may be explained by these data.

Animals↗