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Biomedical subjects

R Viswanathan

Publications and source records attributed to R Viswanathan.

At least 19 recordsLinked to original sources
PubMed2002

Immunology of the pathogen virulence and phytotoxin production in relation to disease severity: a case study in sheath blight of rice.

Polyclonal antibodies against purified Rhizoctonia solani toxin obtained from infected rice sheath tissues (sheath blight toxin, SBT) and culture filtrates (culture filtrate toxin, CFT) were developed in rabbit and chicken. The IgG was isolated from serum and egg yolk of rabbit and chicken, respectively, and their specificity was investigated by indirect ELISA. Antibodies developed against CFT and SBT in rabbits exhibited relatively higher titer values when compared to chicken antibodies. Positive correlation was observed between the degree of sheath blighting and the levels of antigens induced by each isolate during sheath blight symptom development as detected by rabbit SBT antibody and the isolate RS7 was identified as most virulent. Optimization of incubation period for maximum toxin production in liquid medium and rice sheaths indicated that the production of CFT and SBT is maximum after 15 d and 6 d of pathogen inoculation. Studies of the possible translocation of RS-toxin in rice plants upon inoculation with R. solani showed downward translocation as detected by rabbit/chicken SBT antibodies. Since plant inoculation required a higher concentration of inoculum and maintenance of plants, serological assay by ELISA is more sensitive than whole-plant assays in detecting RS-toxin, with the advantage that ELISA also allows rapid determination of RS-toxin production.

Animals↗
PubMed2002

Quality of paper boards from arecanut leaf sheath.

A study was carried on utilizing arecanut leaf sheath for making paper boards. Paper boards were made with various combinations of arecanut leaf sheath with waste paper, 1:1, 1:2, 1:3, 3:1, 2:1, control (100% areca leaf sheath) and the qualities of these paper boards were tested as per the Bureau of Indian Standards (IS: 1060 (part-I)-1966). The paper boards made with more arecanut sheath materials had more resistance to water absorption. The addition of paper increased the substance weight of the paper boards. The 2:1 and 3:1 combinations of arecanut leaf sheath and waste paper had best tear strength, tensile strength, bursting strength and water resistance with minimum substance weight.

Absorption↗
PubMed2001

Nonconventional carbon additions to azomethines. aryl amination/indoline synthesis by direct aryl radical addition to azomethine nitrogen.

[reaction: see text]. The generality of a new method for aryl amination has been defined. Ketimines derived from o-bromophenethylamine cyclize to the N-substituted indoline when treated with nBu3SnH and a radical initiator. The pH-neutral conditions tolerate base- and acid-sensitive functionality. The observed regioselectivity is nonconventional for addition reactions involving carbon radicals and carbon-heteroatom pi-bonds.

Journal Article↗
PubMed2001

Antifungal activity of chitinases produced by some fluorescent pseudomonads against Colletotrichum falcatum Went causing red rot disease in sugarcane.

Chitinase production and growth of certain fluorescent pseudomonads isolated from sugarcane rhizosphere on different subtrates were studied. When chitin was substituted for glycerol in King's B medium, 3 of the 4 strains showed enhanced bacterial multiplication. Bacterial cells grown on chitin-containing medium showed enhanced antifungal activity against Colletotrichum falcatum Went causing red rot disease in sugarcane. Chitinase production was significantly higher when chitin was amended to King's B medium. Higher chitinase production was also recorded when fluorescent pseudomonad strains were grown in the medium containing crab-shell chitin. Cell-free bacterial culture filtrate from chitin-containing medium significantly inhibited mycelial growth of the pathogen. These cell-free conditioned media contained 3 to 7 polypeptides. Western blot analysis revealed five isoforms of chitinase with molecular masses of 47, 36, 32, 20 and 18.5 kDa. A possible role of chitinases in red rot disease management is discussed.

Antifungal Agents↗
PubMed2000

Oral lesions and conditions associated with human immunodeficiency virus infection in 300 south Indian patients.

BACKGROUND: Human immunodeficiency virus infection/acquired immunodeficiency syndrome (HIV/AIDS) is a major health problem in India. The National AIDS Control Organisation (NACO) of India reports a seropositivity of 25.03 per thousand for the whole country, as of October 1999. In spite of this high prevalence there are very few reports of oral lesions and conditions in Indian HIV/AIDS patients, which are important in early diagnosis and management of these patients. OBJECTIVE AND SETTING: The present report describes the oral lesions in 300 HIV positive symptomatic patients presenting to us at RAGAS-YRG CARE, a non-governmental organisation in Chennai, South India, over a period of 9 months in 1998. METHOD: Lesions were diagnosed on clinical appearance using international criteria. RESULTS: Of the 300 patients 89% had acquired the infection through heterosexual contact. There were 205 males and 95 females, aged from 7 months to 72 years. Forty-seven percent of the patients were in the age group 21-30 years. CD4 counts were ascertained for 105 patients, 64 (62%) had CD4 counts < or = 200. A total of 217 (72%) of the 300 patients had some oral lesion when examined. Gingivitis (47%) and pseudomembranous candidiasis (33%) were the most common oral lesions. The other oral lesions seen were oral mucosal pigmentation (23%), erythematous candidiasis (14%), periodontitis (9%), angular cheilitis (8%), oral ulcers (3%), oral hairy leukoplakia (3%), hyperplastic candidiasis (1%), oral submucous fibrosis (2%) and one case of leukoplakia. CONCLUSIONS: Oral lesions occur commonly in HIV infection. A comprehensive oral examination may not only suggest HIV disease but may also be useful in monitoring the disease progression. This is a cost-effective procedure, which may be useful in screening large populations in developing countries like India.

AIDS-Related Opportunistic Infections↗
PubMed1999

Proteinmorphosis: a mechanical model for protein conformational changes.

Proteinmorphosis is a physically-based interactive modeling system for simulating large or small conformational changes of proteins and protein complexes. It takes advantage of the cross-linked one-dimensional nature of protein chains. The user can, based on her chemical knowledge, pull pairs of points (lying either on a single protein or on different molecules) together by specifying geometric distance constraints. The resulting conformation(s) of the molecule(s) of interest is computed by an efficient finite element formalism taking into account elasticity of the protein backbone, van der Waals repulsions, hydrogen bonds, salt bridges and the imposed distance constraints. The conformational change is computed incrementally and the result can be visualized as an animation; complete interactivity is provided to position and view the proteins as desired by the user. Physical properties of regions on the protein can also be chosen interactively. The conformational change of calmodulin upon peptide binding is examined as a first experiment. It is found that the result is satisfactory in reproducing the conformational change that follows on peptide binding. We use Proteinmorphosis to study the cooperative hemoglobin oxygen binding mechanism in a second, more sophisticated, experiment. Different modeling strategies are designed to understand the allosteric (cooperative) binding process in this system and the results are found to be consistent with existing hypotheses.

Calmodulin↗
PubMed1998

Combinatorial electrochemistry: A highly parallel, optical screening method for discovery of better electrocatalysts

Combinatorial screening of electrochemical catalysts by current-voltage methods can be unwieldy for large sample sizes. By converting the ions generated in an electrochemical half-cell reaction to a fluorescence signal, the most active compositions in a large electrode array have been identified. A fluorescent acid-base indicator was used to image high concentrations of hydrogen ions, which were generated in the electrooxidation of methanol. A 645-member electrode array containing five elements (platinum, ruthenium, osmium, iridium, and rhodium), 80 binary, 280 ternary, and 280 quaternary combinations was screened to identify the most active regions of phase space. Subsequent "zoom" screens pinpointed several very active compositions, some in ternary and quaternary regions that were bounded by rather inactive binaries. The best catalyst, platinum(44)/ruthenium(41)/osmium(10)/iridium(5) (numbers in parentheses are atomic percent), was significantly more active than platinum(50)/ruthenium(50) in a direct methanol fuel cell operating at 60 degreesC, even though the latter catalyst had about twice the surface area of the former.

Journal Article↗
PubMed1998

Streptococcal emm types associated with T-agglutination types and the use of conserved emm gene restriction fragment patterns for subtyping group A streptococci.

The T-agglutination types were determined for a diverse collection of 1531 group A streptococci for which the 5' M protein gene (emm) sequences had been analysed. The majority of the T-agglutination types correlated with previously seen M/emm/T-type associations; however, several new associations were found. Analysis of a subset of this collection -- which included 1157 clinical isolates with multiply encountered emm types -- found that emm amplicon restriction profiles of isolates sharing identical T types and opacity factor phenotypes are useful for detecting groups of isolates with identical emm genes. Many emm genes of known 5' sequence display a highly conserved restriction pattern amongst clinical isolates widely separated both geographically and temporally.

Agglutination↗
PubMed1997

Physiological basis in the assessment of ecotoxicity of pesticides to soil organisms.

Earthworms are universally accepted as one of the most suitable and representative soil animals to be used for assessing chemical pollution in soils. Therefore, in this work earthworm species diverse in habitat and life-pattern are used and the effects of sublethal concentrations of terbuthylazine and carbofuran on the reproductive processes, respiration and excretion are investigated. The results show that even low and moderate concentrations of the pesticides can induce measurable physiological effects. Species-specific and substance-specific effects are noticeable in the worms.

Ammonia↗
PubMed1997

Lymphoma of the lumbar nerve root: case report.

BACKGROUND AND IMPORTANCE: Lymphoma deposits in the spine are typically extradural. However, we report the case of a 38-year-old man who had a peripheral T-cell lymphoma with both intra- and extradural involvement. CLINICAL PRESENTATION: The patient presented with a 3-month history of right hip and thigh pain. Computed tomography and magnetic resonance imaging revealed features indistinguishable from those of a benign neurofibroma, except for a small area of T2-weighted signal abnormality in the third lumbar vertebral body. INTERVENTION: A solitary lesion of the right third lumbar root with normal surrounding bone and soft tissue was excised at surgery. At immunohistopathological evaluation, a diagnosis was made of peripheral lymphoma. Postoperative evaluation did not reveal lymphoma in the cerebrospinal fluid, abdomen, chest, blood, or bone marrow. This case illustrates that lymphomas can grow in patterns indistinguishable from a tumor of a nerve root. Therefore, other treatment modalities would have been considered had the diagnosis of lymphoma been made preoperatively. CONCLUSION: Involvement of a solitary nerve root by lymphoma, although rare, should be suspected in all cases of nerve root neurofibroma, and magnetic resonance imaging should be performed. Even minor signal abnormalities in adjoining vertebrae signal the possibility of malignancy. Percutaneous biopsy of suspicious bony lesions and systemic evaluation can demonstrate other sites of involvement, enabling the confirmation of the diagnosis and appropriate treatment without recourse to surgery.

Adult↗
PubMed1996

Acute intraoperative brain herniation during elective neurosurgery: pathophysiology and management considerations.

OBJECTIVES: To describe operative procedures, pathophysiological events, management strategies, and clinical outcomes after acute intraoperative brain herniation during elective neurosurgery. METHODS: Review of clinical diagnoses, operative events, postoperative CT findings, intracranial pressure, and arterial blood pressure changes and outcomes in a series of patients in whom elective neurosurgery had to be abandoned because of severe brain herniation. RESULTS: Acute intraoperative brain herniation occurred in seven patients. In each patient subarachnoid or intraventricular haemorrhage preceded the brain herniation. The haemorrhage occurred after intraoperative aneurysm rupture either before arachnoidal dissection (three) or during clip placement (one); after resection of 70% of a recurrent hemispheric astroblastoma; after resection of a pineal tumour; and after a stereotactic biopsy of an AIDS lesion. In all patients the procedure was abandoned because of loss of access to the intracranial operating site, medical measures to control intracranial pressure undertaken (intravenous thiopentone), an intraventricular catheter or Camino intracranial pressure monitor inserted, and CT performed immediately after scalp closure. The patients were transferred to an intensive care unit for elective ventilation and multimodality physiological monitoring. Using this strategy all patients recovered from the acute ictus and no patient had intracranial pressure > 35 mm Hg. Although one patient with an aneurysm rebled and died three days later the other six patients did well considering the dramatic and apparently catastrophic nature of the open brain herniation. CONCLUSIONS: There are fundamental differences in the pathophysiological mechanisms, neuroradiological findings, and outcomes between open brain herniation occurring in post-traumatic and elective neurosurgical patients. The surprisingly good outcomes in this series may have occurred because the intraoperative brain herniation was secondary to extra-axial subarachnoid or intraventricular haemorrhage rather than intraparenchymal haemorrhage or acute brain oedema. Expeditious abandonment of the procedure and closure of the cranium may also have contributed to the often very satisfactory clinical outcome.

Adult↗
PubMed1996

Detection of sugarcane bacilliform virus in sugarcane germplasm.

Sugarcane bacilliform virus (SCBV), a badnavirus was found in sugarcane genotypes of Saccharum officinarum L., S. barberi Jesw., S. sinense Roxb., S. robustum Brand and Jesw., and Saccharum hybrids. In most of the suspected genotypes the virus was found associated with clear foliar symptoms. However, certain symptom-free clones carried the virus too. The virus was detected by immuno-electron microscopy (IEM) and enzyme-linked immunosorbent assay (ELISA) in suspected clones. The virions measured about 108-118 x 20-21 nm in size. The virus was serologically closely related to another badnavirus, banana streak virus (BSV). Virus titer was low in most of the genotypes. However, a close correlation between symptoms expression and virus titer existed in some genotypes.

Animals↗
PubMed1995

Liquid to hexatic to crystalline order in Langmuir-Blodgett films.

Atomic force microscope images of zinc arachidate (ZnA2) Langmuir-Blodgett films show that three- and five-layer films are "hexatic," with long-range bond-orientational order and short-range positional correlations of three to five lattice repeats. The monolayer in contact with the substrate is disordered. Films of seven or more layers of ZnA2 are crystalline. A population of dislocations, most likely originating at the substrate, disrupts the positional but not the orientational order of the lattice, leading to hexatic layers intermediate between crystal and liquid. The influence of the substrate propagates farther into ZnA2 films than into cadmium arachidate films because the molecular cohesion is much weaker in ZnA2 than in cadmium arachidate, as evidenced by a less dense molecular packing.

Chemical Phenomena↗
PubMed1995

CO2 production in three earthworm species exposed to terbuthylazine and carbofuran in food.

Studies were conducted in the laboratory to determine the influence of sublethal doses of pesticides on the respiration of earthworms. Three different lumbricids were exposed to different concentrations of terbuthylazine and carbofuran for up to 12 weeks by allowing them to feed on contaminated plant material. After different exposure periods the CO2 output of the worms was determined by gas chromatography. High terbuthylazine concentrations generally increased CO2 production, whereas the low concentration tended to decrease it, especially in two of the three species studied. Low carbofuran concentration increased the CO2 expired in all the species; the high dose negatively affected the respiration in Lumbricus terrestris and L. rubellus after 3 weeks and in Eisenia andrei after 4 weeks of exposure.

Animals↗
PubMed1995

The structure and stability of phospholipid bilayers by atomic force microscopy.

Atomic force microscopy (AFM) was used to investigate the structure, stability, and defects of the hydrophilic surfaces of Langmuir-Blodgett bilayer films of distearoylphosphatidylcholine (DSPC) and dipalmitoylphosphatidylethanolamine (DPPE) in the solid phase, and dilinoleoylphosphatidylethanolamine (DLPE) in the fluid phase. Their relative resilience to external mechanical stress by the scanning tip and by fluid exchange were also investigated. DPPE monolayers showed parallel ridges at the surface with a period of 0.49 nm, corresponding to the rows of aligned headgroups consistent with the known crystallographic structure. DSPC and DLPE monolayers did not show any periodic order. The solid DSPC and DPPE monolayers were stable to continued rastering by the AFM tip; however, the stability of DLPE monolayers depended on the pH of the aqueous environment. Structural defects in the form of monolayer gaps and holes were observed after fluid exchange, but the defects in DLPE monolayer at pH 11 were stable during consecutive scanning. At pH 9 and below, the defects induced by fluid exchange over DLPE monolayers were more extensive and were deformed easily by consecutive scanning of the AFM tip at a force of 10 nN. The pH dependence of resilience was explained by the increasing bending energy or frustration due to the high spontaneous curvature of DLPE monolayers at low pH. The tangential stress exerted by the AFM tip on the deformable monolayers eventually produced a ripple pattern, which could be described as a periodic buckling known as Shallamach waves.

Biophysical Phenomena↗