Search PubMed⌕ Search

Biomedical subjects

M C Roberts

Publications and source records attributed to M C Roberts.

At least 73 records · Page 4Linked to original sources
PubMed1997

Induction of surface fluidity in Trichinella spiralis larvae during penetration of the host intestine: simulation by cyclic AMP in vitro.

The lateral diffusion (DL) properties of the fluorescent lipid probe 5-N (octadecanoyl) aminofluorescein (AF18) inserted into the surface of muscle-stage larvae of Trichinella spiralis were investigated by fluorescence recovery after photo-bleaching. AF18 was not free to diffuse laterally in dormant larvae, and this remained unchanged after larval activation in vitro with trypsin and bile. However, a significant increase in surface fluidity of the probe was demonstrated (%R = 74.5; DL = 11.5 x 10(-9) cm2/sec) when larvae invaded intestinal epithelial tissue following oral infection of mice. Membrane-permeant photoactivatable caged cyclic AMP was used to analyse the putative mechanism responsible for this increase in lateral diffusion in the parasite surface. Although incubation of larvae with 1-50 microM caged cAMP had no effect on surface fluidity, incubation with 100 microM caged cAMP induced a substantial increase in the lateral mobility of AF18 (%R = 64.3; DL = 8.3 x 10(-11) cm2/sec) immediately following photo-activation of the caged messenger. This induced fluidity, however, was transient and the larval surface reverted to immobility within 15 min. These observations constitute the first reported measurement of the fluid properties of the surface of intracellular parasites, the first demonstration of the parasite surface fluidity altering as a result of host cell invasion and the first indication of a mechanism underlying changes in surface fluidity in parasitic helminths.

Animals↗
PubMed1997

Distribution and mobility of the tetracycline resistance determinant tetQ.

We tested 34 American Type Culture Collection (ATCC) and 168 clinical bacterial isolates, from the human urogenital and oral tracts and streptococci isolated from cows with mastitis, for the presence of the tetQ gene using a polymerase chain reaction (PCR) assay and DNA-DNA hybridization. The identities of PCR products were confirmed by Southern blot hybridization of whole-cell DNA. Eleven of the ATCC strains were positive for tetQ, including five Bacteroides spp., five Prevotella spp. and a single isolate of Mitsuokella multiacidus. Twenty-eight (29%) of the 95 clinical Gram-negative isolates carried the tetQ gene, while eight (11%) of the 73 clinical Gram-positive isolates carried the tetQ gene. This is the first description of tetQ in Gram-positive species. All isolates except one Peptostreptococcus sp. carried tetQ integrated into the chromosome. The tetQ gene could be transferred from Prevotella bivia, Bacteroides ovatus, Bacteroides fragilis, Bacteroides vulgatus and Bacteroides distasonis into an Enterococcus faecalis recipient at frequencies of 10(-7)-10(-9) per recipient. In contrast, tetQ failed to transfer from two isolates of Prevotella intermedia, two isolates of Porphyromonas gingivalis, one isolate of Mobiluncus curtisii and one isolate of Peptostreptococcus sp. The latter two are Gram-positive species. The PCR assay was used to screen 198 proteinase K-treated biopsies of prostate, periprostate and bladder from 84 men with prostatitis. Thirty-four (40%) of the patients had one or more positive samples, suggesting that the PCR assay could be of value in screening patient material directly for the presence of bacteria.

Animals↗
PubMed1997

Genomic homogeneity of the AHU/IA-1,2 phenotype of Neisseria gonorrhoeae during its disappearance from an urban population.

BACKGROUND: Isolates of Neisseria gonorrhoeae requiring arginine, hypoxanthine, and uracil (AHU) appeared in Denmark in 1946, were preponderant in Seattle during the 1970s, were associated with disseminated gonococcal infections (DGI), and were primarily of the IA-1,2 serovar. GOALS: To investigate the disappearance of the AHU/IA-1,2 phenotype and to examine by pulsed-field gel electrophoresis (PFGE) the genomic homogeneity of this unique phenotype isolated from Seattle-King County during the past decade. STUDY DESIGN: This retrospective study used data extracted from previous publications for the period 1971 through 1984, and from existing records at the Neisseria Reference Laboratory, University of Washington for the period 1985 through 1996. Samples (n = 68) of AHU/IA-1,2 isolates from 1984 to 1985 and 1988 to 1993 were analyzed using endonucleases NheI and XbaI. For comparison, 10 AHU/IB isolates were included in the study. RESULTS: AHU isolates, predominantly IA-1,2 strains accounted for 52% of the gonococcal isolates for the period 1971 through 1974, 40% for 1974 through 1976, 16% for 1984, and then declined from 7% in 1986 to 0% for each of the last 3 years, 1994 through 1996. Isolates with < or = 1 band difference after digestion with either NheI or XbaI were considered to belong to a single closely related pattern. Pulsed-field gel electrophoresis (PFGE) type designation was made from the combination of NheI and XbaI patterns. These criteria yielded 5 NheI and 8 XbaI PFGE patterns, and 11 PFGE types based on the combination of NheI and XbaI pattern. The most frequently occurring NheI and XbaI patterns accounted for 74% and 57% of isolates, respectively. One type persisted throughout the decade and accounted for 54% of the 68 isolates. Analysis of the 10 AHU/IB isolates yielded 7 NheI and 8 XbaI patterns that gave 9 types that were distinct from the types found in the AHU/IA-1,2 strains. CONCLUSION: The AHU/IA-1,2 phenotype first documented 50 years ago in Denmark still shows a high degree of genomic homogeneity during the past decade in Seattle. The implementation of screening, decreased rates of sexual exposure in the acquired immune deficiency syndrome era, or other factors may explain its apparent elimination in Seattle-King County.

Electrophoresis, Gel, Pulsed-Field↗
PubMed1997

Mycobacterium tuberculosis efpA encodes an efflux protein of the QacA transporter family.

The Mycobacterium tuberculosis H37Rv efpA gene encodes a putative efflux protein, EfpA, of 55,670 Da. The deduced EfpA protein was similar in secondary structure to Pur8, MmrA, TcmA, LfrA, EmrB, and other members of the QacA transporter family (QacA TF) which mediate antibiotic and chemical resistance in bacteria and yeast. The predicted EfpA sequence possessed all transporter motifs characteristic of the QacA TF, including those associated with proton-antiport function and the motif considered to be specific to exporters. The 1,590-bp efpA open reading frame was G+C rich (65%), whereas the 40-bp region immediately upstream had an A+T bias (35% G+C). Reverse transcriptase-PCR assays indicated that efpA was expressed in vitro and in situ. Putative promoter sequences were partially overlapped by the A+T-rich region and by a region capable of forming alternative secondary structures indicative of transcriptional regulation in analogous systems. PCR single-stranded conformational polymorphism analysis demonstrated that these upstream flanking sequences and the 231-bp, 5' coding region are highly conserved among both drug-sensitive and multiply-drug-resistant isolates of M. tuberculosis. The efpA gene was present in the slow-growing human pathogens M. tuberculosis, Mycobacterium leprae, and Mycobacterium bovis and in the opportunistic human pathogens Mycobacterium avium and Mycobacterium intracellular. However, efpA was not present in 17 other opportunistically pathogenic or nonpathogenic mycobacterial species.

Amino Acid Sequence↗
PubMed1997

Genetic mobility and distribution of tetracycline resistance determinants.

Since 1953, tetracycline-resistant bacteria have been found increasingly in humans, animals, food and the environment. Tetracycline resistance is normally due to the acquisition of new genes and is primarily due to either energy-dependent efflux of tetracycline or protection of the ribosomes from its action. Gram-negative efflux genes are frequently associated with conjugative plasmids, whereas Gram-positive efflux genes are often found on small mobilizable plasmids or in the chromosome. The ribosomal protection genes are generally associated with conjugative transposons which have a preference for the chromosome. Recently, tetracycline resistance genes have been found in the genera Mycobacterium, Nocardia, Streptomyces and Treponema. The Tet M determinant codes for a ribosomal protection protein which can be found in Gram-positive, Gram-negative, cell-wall-free, aerobic, anaerobic, pathogenic, opportunistic and normal flora species. This promiscuous nature may be correlated with its location on a conjugative transposon and its ability to cross most biochemical and physical barriers found in bacteria. The Tet B efflux determinant is unlike other efflux gene products because it confers resistance to tetracycline, doxycycline and minocycline and has the widest host range of all Gram-negative efflux determinants. We have hypothesized that mobility and the environment of the bacteria may help influence the ultimate host range of specific tet genes. If we are to reverse the trend towards increasingly antibiotic-resistant pathogenic bacteria, we will need to change how antibiotics are used in both human and animal health as well as food production.

Bacteria↗
PubMed1997

Pharmacokinetics of cisapride in horses after intravenous and rectal administration.

OBJECTIVES: To determine the i.v. pharmacokinetics of cisapride and measure systemic absorption after rectal administration. ANIMALS: 5 healthy adult mares (380 to 610 kg). PROCEDURE: Cisapride was administered, i.v., at a dosage of 0.1 mg/kg of body weight. In the same horses, after a 1-week washout period, cisapride was administered rectally at a dosage of 1 mg/kg by mixing crushed tablets with propylene glycol and administering the mixture into the rectum. After each drug administration, a series of blood samples were collected. Plasma was obtained and analyzed by high-performance liquid chromatography to determine cisapride concentration profiles after each drug administration. RESULTS: After i.v. administration, peak plasma concentration was 221.4 ng/ml and harmonic mean half-life was 1.9 hours. Rectal absorption of cisapride was negligible. Cisapride was detected in plasma from only 3 of 5 horses for which mean systemic availability was 1.23%. Mean maximal plasma concentration after rectal administration of cisapride was 13.5 ng/ml. CONCLUSION AND CLINICAL RELEVANCE: After i.v. administration of cisapride, plasma concentration is high for approximately 2 hours. Cisapride mixed with propylene glycol and administered rectally at a dosage of 1 mg/kg is poorly and incompletely absorbed. Thus, cisapride is not clinically useful for rectal administration in horses.

Absorption↗
PubMed1996

Serotonergic agents in the treatment of hypothalamic obesity syndrome: a case report.

The hypothalamic obesity syndrome is characterized by hyperphagia and excessive weight gain in the presence of demonstrable hypothalamic injury. There have been no previous reports describing the use of serotonergic agents in this condition. We report on a patient with severe hyperphagia and obesity secondary to a hypothalamic lesion, who was treated with consecutive courses of fluoxetine and fenfluramine. Neither treatment resulted in a reduction in food intake or weight. Treatment of hypothalamic obesity with serotonergic agents appears to be of little value, probably because they exert their effect via intact serotonergic-sensitive hypothalamic nuclei.

Adult↗
PubMed1996

Schistosomes and serpins: a complex business.

The view of the schistosome host-parasitic relationship has changed in the past two decades. Previously, it was thought the parasite simply defended itself in the face of a hostile host environment. However, it is now realized that the host-parasite interaction is much more of a dynamic interplay, where the parasite is able to exploit host homeostatic mechanisms for survival, maturity and transmission. Here, Jay Modha, Clare Roberts and John Kusel discuss the recent identification of serine protease inhibitors (serpins) on the schistosome surface and suggest how their properties might be exploited by the parasite.

Journal Article↗
PubMed1996

Characterization of tetracycline and erythromycin resistance in Actinobacillus pleuropneumoniae.

Minimum inhibitory concentrations to tetracycline and erythromycin were determined for nineteen isolates of Actinobacillus pleuropneumoniae of Norwegian origin. The isolates were screened for rRNA methylase determinants (Erm genes) and for the tetracycline resistance Tet B determinant, using oligonucleotide probes, polymerase chain reaction and hybridization. Ten isolates (53%) carried the Erm C determinant, two isolates (10%) carried the Erm A determinant, four isolates (21%) carried both the Erm A and the Erm C determinants, and three isolates (16%) carried none of the Erm determinants examined. Eight isolates (45%) carried the Tet B determinant. Selected isolates were shown to transfer the Erm C and Erm A determinants at a frequency of 10(-7)-10(-9) per recipient cell. This is the first description of A. pleuropneumoniae carrying either Erm A, Erm C or/and Tet B determinants.

Actinobacillus Infections↗
PubMed1996

Early adolescents exposed to violence: hope and vulnerability to victimization.

Eighty-nine early adolescents were measured for perceptions of hope, exposure to violence, and perceived vulnerability to victimization. Results showed the presence of high hope, together with a high degree of exposure to violence. The adolescents were about equally divided regarding the nature of their own death, while most predicted a violent death for the "average American." The highest levels of hope were reported by those who had witnessed violence but not experienced it personally; those with the greatest exposure to violence predicted their own death would be violent.

Child↗
PubMed1996

Mobile rRNA methylase genes coding for erythromycin resistance in Actinobacillus actinomycetemcomitans.

We found that 17 (68%) of 25 Actinobacillus actinomycetemcomitans isolated from periodontally diseased sites had MICs of erythromycin > or = 8 mg/L. The isolates were hybridized with five rRNA methylase genes and gene mobility was determined. Twenty-four (96%) of 25 isolates hybridized with one or more rRNA methylase genes. Representative isolates were able to transfer erythromycin resistance to Haemophilus influenzae and Enterococcus faecalis recipients. The transconjugants were shown to carry rRNA methylase genes by DNA probe hybridization and had MICs of erythromycin 32 to 256 mg/L.

Aggregatibacter actinomycetemcomitans↗
PubMed1996

Children's perceptions of peers with AIDS: assessing the impact of contagion information, perceived similarity, and illness conceptualization.

Assessed factors that affected acceptance of a hypothetical peer with AIDS. Children in Grades 4-6 read vignettes containing one of four levels of contagion information and one of two levels of perceived similarity. Illness conceptualization was measured as a continuous variable. Results indicated that the type of AIDS information given to children affected their perception of the peer. Specifically, informing children about the modes of HIV transmission was not sufficient to increase acceptance, but clearing misconceptions by describing ways HIV is not transmitted positively affected children's reactions to the peer. No other significant results were found. Results of the current study have clear and practical implications for AIDS education programs in schools.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Tetracycline resistance determinants: mechanisms of action, regulation of expression, genetic mobility, and distribution.

Tetracycline-resistant bacteria were first isolated in 1953 from Shigella dysenteriae, a bacterium which causes bacterial dysentery. Since then tetracycline-resistant bacterial have been found in increasing numbers of species and genera. This has resulted in reduced effectiveness of tetracycline therapy over time. Tetracycline resistance is normally due to the acquisition of new genes often associated with either a mobile plasmid or a transposon. These tetracycline resistance determinants are distinguishable both genetically and biochemically. Resistance is primarily due to either energy-dependent efflux of tetracycline or protection of the ribosomes from the action of tetracycline. Gram-negative tetracycline efflux proteins are linked to repressor proteins which in the absence of tetracycline block transcription of the repressor and structural efflux genes. In contrast, expression of the Gram-positive tetracycline efflux genes and some of the ribosomal protection genes appears to be regulated by attenuation of mRNA transcription. Specific tetracycline resistance genes have been identified in 32 Gram-negative and 22 Gram-positive genera. Tetracycline-resistant bacteria are found in pathogens, opportunistic and normal flora species. Tetracycline-resistant bacteria can be isolated from man, animals, food, and the environment. The nonpathogens in each of these ecosystems may play an important role as reservoirs for the antibiotic resistance genes. It is clear that if we are to reverse the trend toward increasingly antibiotic-resistant pathogenic bacteria we will need to change how antibiotics are used in both human and animal health and food production.

Animals↗
PubMed1996

Integration of pT181-like tetracycline resistance plasmids into large staphylococcal plasmids involves IS257.

Four large staphylococcal plasmids ranging in size from 31 to 82 kbp have been shown to mediate tetracycline resistance via an integrated copy of the tet(K)-encoding plasmid pT181 which was flanked by copies of the insertion element IS257. In two cases, IS257 elements interrupted the repC reading frame of pT181 and an 8-bp sequence from within the repC gene was duplicated at the interrupted site. In the third plasmid, the IS257 elements interrupted the pT181 DNA immediately upstream of the repC coding sequence with an 8-bp duplication. In the fourth case, the IS257 elements flanked a pT181-like plasmid with one IS257 in the repC coding sequence and the other within the recombinase (pre) coding sequence, so that a section of the pT181 sequence was deleted. All four integration sites detected in this study differ from those previously described for the IS257-mediated integration of pT181-like plasmids into large plasmids or into the chromosomal DNA.

Blotting, Southern↗