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Biomedical subjects

S Nalini

Publications and source records attributed to S Nalini.

15 recordsLinked to original sources
PubMed2006

Comparison of double disc and three dimensional methods to screen for ESBL producers in a tertiary care hospital.

Extended spectrum beta lactamases (ESBLs) continue to be a major problem in clinical setups world over, conferring resistance to the expanded spectrum cephalosporins. An attempt was made to study ESBL production among Enterobacteriaceae members from a tertiary care center in Chennai. A total of seventy randomly collected isolates of the family Enterobacteriaceae from a tertiary care center was studied for their susceptibility patterns to various antibiotics and detection of ESBL producers by double disc synergy (DDS) test and three dimensional test (TDT). Eighty percent of the isolates were multidrug resistant (MDR) and 20% were ESBL producers. TDT detected 85.7% whereas only 14.2% were detected by DDS. In the present study, a large number of isolates were found to be MDR and ESBL producers. TDTs were found to be better than DDS in the detection of ESBLs. Continued monitoring of drug resistance is necessary in clinical settings for proper disease management.

Anti-Bacterial Agents↗
PubMed2001

Comparison of different methods of assessing in vitro resistance of Mycobacterium tuberculosis to rifampicin.

BACKGROUND & OBJECTIVES: Definitions of in vitro resistance to rifampicin in strains of Mycobacterium tuberculosis by different methods have not been consistent, leading to variations in the interpretation and validity of results. This study compared three methods of defining in vitro resistance to rifampicin. METHODS: (i) A total of 598 clinical isolates of M. tuberculosis were concurrently compared by the minimal inhibitory concentration (MIC) and the proportion method on Lowenstein-Jensen medium; (ii) 54 strains tested by the MIC method were retested by the proportion method and the BACTEC radiometric method; and (iii) 72 strains which yielded an MIC of 64 mg/l by the MIC method were retested by the same method. RESULTS: Out of 598 cultures tested by the MIC and the proportion methods, identical classification as susceptible or resistant was observed in 99.7 per cent. A 100 per cent agreement was observed when 54 strains were tested by the MIC, proportion and BACTEC radiometric methods. When 72 strains with an MIC of 64 mg/l were retested by the same method, 61 (85%) yielded a lower MIC, 9 (12%) gave the same MIC while 2 (3%) yielded a higher MIC of 128 mg/l, reflecting perhaps the inherent limitations of the variations in the inoculum size. INTERPRETATION & CONCLUSION: All 3 definitions of resistance, viz., an MIC of 128 mg/l, a proportion of 1 per cent or more on 40 mg/l by the proportion method, both on L-J medium and a growth of 1 per cent or more on 2 mg/l by the radiometric method were found to be equally satisfactory.

Antibiotics, Antitubercular↗
PubMed1994

Studies on acid soluble thiols in the human gastric juice.

Human gastric juice was found to contain high levels of thiols as detected by reaction with dithionitrobenzoic acid (Ellman's reagent). Analysis of gastric juice for glutathione and cysteine, the known acid soluble thiols in biological system, by HPLC and calorimetric methods, indicated that they are absent in the gastric juice. Further studies on the nature of thiols in the gastric juice, by Sephadex G-25 gel filtration indicated the presence of both high and low molecular weight protein and peptide associated thiols. Dialysis of the gastric juice retained nearly 70% thiols in non-dialysable fraction. These studies suggest that biologically important low molecular weight thiols, glutathione and cysteine are absent in the human gastric juice and the thiols detected are mainly acid soluble proteins and possibly peptide associated thiols.

Chromatography, Gel↗
PubMed1993

Oxygen free radical induced damage during intestinal ischemia/reperfusion in normal and xanthine oxidase deficient rats.

This study looks at the role of xanthine oxidase (XO) in ischemia/reperfusion (I/R) induced intestinal mucosal damage using normal and xanthine oxidase deficient rats. Tungstate feeding for 3 days depleted the intestinal mucosal XO by 80%. A ligated loop of the rat small intestine (both normal and XO-deficient) was subjected to 1 h of total ischemia followed by 5 min revascularisation. The ensuing mucosal damage was assessed by biochemical and histological studies. Ischemia or I/R increased the XO levels in normal rats without any change in XO-deficient rats. Myeloperoxidase (a neutrophil marker) level was increased in both group of rats but it was comparatively higher in the XO-deficient rats. Accumulation of peroxidation products such as malondialdehyde, conjugated diene and increased production of hydroxyl radicals by microsomes were seen after ischemia and I/R and were similar in normal and XO-deficient rats. Studies on other parameters of peroxidation showed a decrease in polyunsaturated fatty acids and alpha-tocopherol, an increase in cysteine and cystine levels after I/R and were similar in both normal and XO-deficient rats. Histological results indicated gross morphological changes in the intestinal mucosa due to ischemia and I/R, and the damage was more severe in XO-deficient rats. These observations suggest that oxygen-derived free radicals are involved in the intestinal mucosal damage during I/R and infiltrated neutrophils rather than XO may be the primary source of free radicals under these conditions.

Animals↗
PubMed1993

Effect of oxidant exposure on monkey intestinal brush-border membrane.

This study looks at the effect of oxidant exposure on changes in structural components and functional properties of monkey intestinal brush-border membrane vesicles (BBMV). These membranes were found resistant to iron-dependent lipid peroxidation as judged by measurement of various parameters such as formation of malonaldehyde (MDA) and conjugated diene and depletion of total arachidonic acid, tocopherol and membrane-associated protein thiol groups. Free radicals generated by thermal decomposition of 2,2'-azobis(2-amidinopropane) dihydrochloride (ABAP) which does not require iron, were capable of inducing lipid peroxidation in this membrane. Fluorescence polarisation studies used to assess the physical state of the membrane lipids after exposure to various free radical generating systems showed that ABAP could decrease the fluidity of BBMV whereas other systems had no effect. Exposure of BBMV to ABAP or cumene hydroperoxide decreased the glucose and amino acid transport. BBMV had a high content of nonesterified fatty acids as part of the total lipids and removal of these free fatty acids by treatment with fatty acid free albumin made the membranes susceptible to iron-dependent peroxidation. These studies suggest that intestinal epithelial cell membranes are resistant to iron-dependent lipid peroxidation due to the presence of membrane-associated free fatty acids. Possibly lipid peroxidation may play a less significant role in damage to these cells.

Amino Acids↗
PubMed1993

Effect of luminal exposure of oxidants on intestinal mucosal lipid peroxidation and absorptive function.

The lumen of the gastrointestinal tract is likely to have free iron and prooxidants that might generate free radicals, resulting in structural and functional damage to the absorptive cells. In the present study the effect of luminal exposure of different oxidants on intestinal mucosal lipid peroxidation and absorptive function in anaesthetized animals has been studied. Oxidants that require iron for free radical generation did not have any effect on the mucosa, whereas free radicals generated by using 2,2'azobis (2-amidino propane) dihydrochloride or menadione, which do not require iron, resulted in lipid peroxidation as assessed by malonaldehyde and conjugated diene formation and depletion of the antioxidant alpha-tocopherol. These oxidants also induced water and electrolyte secretion as studied by luminal perfusion. This observation is physiologically significant since the presence of prooxidants along with iron in the lumen may not have a damaging effect on the mucosa.

Amidines↗
PubMed1993

Studies on iron binding by free fatty acids.

The effect of various saturated and unsaturated fatty acids on iron binding and the translocation of this complex into the organic phase were studied. The amount of iron translocated into the organic phase depended on the affinity of the respective fatty acid to iron. It was seen that saturated and monounsaturated fatty acids translocated more iron compared to polyunsaturated fatty acids. Positional isomers of oleic acid were as effective as oleic acid in translocating iron. It appears that the free carboxyl group on the fatty acid is essential, as the methyl ester of the fatty acid failed to translocate iron. Effect of varying the concentration of fatty acid and iron on iron translocation suggested the requirement of 3 to 4 moles of fatty acid for 1 mole of iron binding. Divalent cations such as Ca2+ and Mg2+ or lipids such as cholesterol or triolein did not compete with fatty acids but there was reduced translocation when phosphate buffer or phospholipid was included in the incubation medium, suggesting that phosphate interferes with the formation of fatty acid-iron complex. Thus it seems that free fatty acids are capable of forming a complex with iron.

Fatty Acids, Nonesterified↗
PubMed1992

Nonesterified fatty acids and lipid peroxidation.

Oxygen free radicals damage cells through peroxidation of membrane lipids. Gastrointestinal mucosal membranes were found to be resistant to in vitro lipid peroxidation as judged by malonaldehyde and conjugated diene production and arachidonic acid depletion. The factor responsible for this in this membrane was isolated and chemically characterised as the nonesterified fatty acids (NEFA), specifically monounsaturated fatty acid, oleic acid. Authentic fatty acids when tested in vitro using liver microsomes showed similar inhibition. The possible mechanism by which NEFA inhibit peroxidation is through iron chelation and iron-fatty acid complex is incapable of inducing peroxidation. Free radicals generated independent of iron was found to induce peroxidation of mucosal membranes. Gastrointestinal mucosal membranes were found to contain unusually large amount of NEFA. Circulating albumin is known to contain NEFA which was found to inhibit iron induced peroxidation whereas fatty acid free albumin did not have any effect. Addition of individual fatty acids to this albumin restored its inhibitory capacity among which monounsaturated fatty acids were more effective. These studies have shown that iron induced lipid peroxidation damage is prevented by the presence of nonesterified fatty acids.

Animals↗
PubMed1991

Effect of exposure of various oxidants on rat liver and intestinal microsomes--a comparative study.

Rat liver and intestinal microsomes were exposed to various free radical generating systems and their effect were assessed by studying different parameters such as formation of malonaldehyde (MDA) and conjugated diene, arachidonic acid depletion and alteration in protein thiol groups and tocopherol levels. These studies revealed that liver being highly vulnerable tissue showed all the effects of free radical attack whereas intestinal microsomes were resistant to most oxidants except iron independent generation of free radicals using 2-2'-azobis (2-amidinopropane) dihydrochloride (ABAP). Intestinal microsomes were found to contain considerable amount of non-esterified fatty acids in total lipid fraction as compared to liver microsomes and iron-fatty acid complex may be incapable of participating in peroxidation. In vitro measurement of hydroxyl radical generation showed that intestinal microsomes were incapable of generating these active species. These results suggest that iron dependent free radical mediated lipid peroxidation might not occur in intestinal epithelial cells.

Amidines↗
PubMed1989

Nonesterified fatty acids inhibit iron-dependent lipid peroxidation.

The effect of various fatty acids on lipid peroxidation of liver microsomes induced by different methods in vitro was studied using oxygen uptake and malonaldehyde (MDA) production. It was observed that fatty acids with a single double bond are effective inhibitors of peroxidation. Stereo and positional isomers of oleic acid were equally effective as oleic acid. There was an absolute requirement for a free carboxyl group, since methyl esters of fatty acids and long-chain saturated and unsaturated hydrocarbons could not inhibit peroxidation. Saturated fatty acids with a chain length of 12-16 carbon atoms showed inhibition, whereas more than 18 carbon atoms reduced the inhibitory capacity. Fatty acids of lower chain length such as capric and caprylic acids did not show inhibition. Fatty acid inhibition was partially reversed by increasing the concentration of iron in the system. Peroxidation induced by methods which were independent of iron was not inhibited by fatty acids. It was observed that intestinal microsomes which were resistant to peroxidation due to the presence of nonesterified fatty acids in their membrane lipids were able to peroxidise by methods which do not require iron. These results suggest that certain fatty acids inhibit peroxidation by chelating available free iron. In addition, they may also be involved in competing with the esterified fatty acids in the membrane lipids which are the substrates for peroxidation.

Adenosine Diphosphate↗
PubMed1989

Albumin bound nonesterified fatty acids inhibit in vitro lipid peroxidation.

Individual nonesterified fatty acids were bound to albumin in vitro and these fatty acid albumin complexes were used to study their effect on lipid peroxidation in liver microsomes. Peroxidation was induced by various methods and malondialdehyde (MDA) was measured as an index of peroxidation. Among the fatty acids tested, albumin-bound monounsaturated fatty acids showed more inhibition of peroxidation as compared to other fatty acids. Increasing the concentration of iron in the peroxidizing system, partially reversed the inhibition by fatty acids. Moreover, albumin-bound fatty acid did not inhibit iron independent peroxidation. This suggests that, like nonesterified fatty acids, albumin-bound fatty acids inhibit peroxidation by chelating the iron. Albumin fatty acid complex, similar to the fatty acid composition present in the circulating albumin, also showed inhibition of peroxidation. These data indicate that nonesterified fatty acids even when bound to albumin are capable of inhibiting peroxidation and circulating albumin, which contains various fatty acids bound to it, may impart some antioxidant effect in addition to other plasma antioxidants.

Albumins↗
PubMedDate not supplied

Hydroxyl radical formation in human gastric juice.

The hydroxyl radical is the most potent free radical derived from oxygen, and has been implicated in damage caused to the gastroduodenal mucosa. The ability of human gastric juice to generate hydroxyl radicals has been investigated in 54 adults with endoscopically normal gastroduodenal mucosa and in 39 patients with chronic duodenal ulcer. Hydroxyl radical production was measured by the formation of formaldehyde from dimethylsulfoxide. Unlike other body fluids, this reaction could proceed without the extraneous addition of catalysts such as hydrogen peroxide (H2O2), ascorbate and iron. Measurement of H2O2, iron and ascorbate showed that these catalysts are already present in the gastric juice. There was no significant difference in the concentration of these components in gastric juice between normal subjects and patients with duodenal ulcer, except that H2O2 levels were slightly higher in duodenal ulcer patients. Although generation of free radicals has been investigated in other body fluids, this is the first reported case regarding the production of these active species in normal human gastric juice. Since hydroxyl production is not significantly enhanced in duodenal ulcer, we suggest that attention may be turned to mucosal antioxidant defences in this disease.

Adolescent↗