Time dependent enhanced resistance against antibiotics & metal salts by planktonic & biofilm form of Acinetobacter haemolyticus MMC 8 clinical isolate.

BACKGROUND & OBJECTIVES: Available literature shows paucity of reports describing antibiotic and metal resistance profile of biofilm forming clinical isolates of Acinetobacter haemolyticus. The present study was undertaken to evaluate the antibiotic and metal resistance profile of Indian clinical isolate of A. haemolyticus MMC 8 isolated from human pus sample in planktonic and biofilm form. METHODS: Antibiotic susceptibility and minimum inhibitory concentration were determined employing broth and agar dilution techniques. Biofilm formation was evaluated quantitatively by microtiter plate method and variation in complex architecture was determined by scanning electron microscopy. Minimum biofilm inhibiting concentration was checked by Calgary biofilm device. RESULTS: Planktonic A. haemolyticus MMC 8 was sensitive to 14 antibiotics, AgNO 3 and HgC1 2 resistant to streptomycin and intermediately resistant to netilmycin and kanamycin. MMC 8 exhibited temporal variation in amount and structure of biofilm. There was 32-4000 and 4-256 fold increase in antibiotic and metal salt concentration, respectively to inhibit biofilm over a period of 72 h as against susceptible planktonic counterparts. Total viable count in the range of 10(5)-10(6) cfu / ml was observed on plating minimum biofilm inhibiting concentration on Muller-Hinton Agar plate without antimicrobial agents. Biofilm forming cells were several folds more resistant to antibiotics and metal salts in comparison to planktonic cells. Presence of unaffected residual cell population indicated presence of persister cells. INTERPRETATION & CONCLUSIONS: The results indicate that biofilm formation causes enhanced resistance against antibiotics and metal salts in otherwise susceptible planktonic A. haemolyticus MMC 8.

Purification of beta-galactosidase from Erythrina indica: involvement of tryptophan in active site.

beta-Galactosidase (EC: 3.2.1.23), one of the glycosidases detected in Erythrina indica seeds, was purified to 135 fold. Amongst the four major glycosidases detected beta-galactosidase was found to be least glycosylated, and was not retained by Con-A CL Seralose affinity matrix. A homogenous preparation of the enzyme was obtained by ion-exchange chromatography, followed by gel filtration. The enzyme was found to be a dimmer with a molecular weight of 74 kDa and 78 kDa, by gel filtration and SDS-PAGE, respectively. The optimum pH and optimum temperature for enzyme activity were 4.4 and 50 degrees C, respectively. The enzyme showed a K(m) value of 2.6 mM and V(max) of 3.86 U/mg for p-nitrophenyl-beta-D-galactopyranoside as substrate and was inhibited by Zn(2+) and Hg(2+). The enzyme activity was regulated by feed back inhibition as it was found to be inhibited by beta-D-galactose. Chemical modification studies revealed involvement of tryptophan and histidine for enzyme activity. Involvement of tryptophan was also supported by fluorescence studies and one tryptophan was found to be present in the active site of beta-galactosidase. Circular dichroism studies revealed 37% alpha helix, 27% beta sheet and 38% random coil in the secondary structure of the purified enzyme.

Characterization of a lectin from Gonatanthus pumilus D. Don having anti-proliferative effect against human cancer cell lines.

A monocot araceous lectin from tubers of Gonatanthus pumilus (GPL) wa earlier purified in our laboratory and reported as T-cell mitogen having homotetrameric structure with subunit molecular mass of 13 kDa. Besides asialofetuin as reported earlier, in the present study it was also inhibited by N-acetyl-D-lactosamine but was non-reactive towards mannose or its derivatives. The lectin is rich in acidic amino acids and cysteine is completely absent. Chemical modification of GPL revealed requirement of tryptophan and tyrosine for lectin sugar interaction. The secondary structure content of GPL, as estimated with CD spectrum in K2D programme, has 73% alpha-helix, 26% beta-sheet and 38% random contributions. Fluorescence spectrum of the lectin solution at 280 nm was typical for tryptophan residues buried inside the protein. Lectin activity decreased when treated with denaturants like guanidine-HCL, urea and thiourea. GPL inhibited the growth of three plant pathogenic fungi namely Colletotrichum lindemuthianum, Fusarium oxysporum and Botrytis cinerea. Out of 11 human cancer cell lines tested, GPL significantly inhibited proliferation of five lines viz. Colo-205, IMR-32, HCT-15, SK-N-SH and HT-29.

Characterization of alpha-mannosidase from Erythrina indica seeds and influence of endogenous lectin on its activity.

alpha-mannosidase from Erythrina indica seeds is a Zn(2+) dependent glycoprotein with 8.6% carbohydrate. The enzyme has a temperature optimum of 50 degrees C and energy of activation calculated from Arrhenius plot was found to be 23 kJ mol(-1). N-terminal sequence up to five amino acid residues was found to be DTQEN (Asp, Thr, Gln, Glu, and Asn). In chemical modification studies treatment of the enzyme with NBS led to total loss of enzyme activity and modification of a single tryptophan residue led to inactivation. Fluorescence studies over a pH range of 3-8 have shown tryptophan residue to be in highly hydrophobic environment and pH change did not bring about any appreciable change in its environment. Far-UV CD spectrum indicated predominance of alpha-helical structure in the enzyme. alpha-Mannosidase from E indica exhibits immunological identity with alpha-mannosidase from Canavalia ensiformis but not with the same enzyme from Glycine max and Cicer arietinum. Incubation of E. indica seed lectin with alpha-mannosidase resulted in 35% increase in its activity, while no such activation was observed for acid phosphatase from E. indica. Lectin induced activation of alpha-mannosidase could be completely abolished in presence of lactose, a sugar specific for lectin.

Purification and partial characterization of alpha-D-mannosidase from Erythrina indica seeds.

Alpha-D-Mannosidase (EC: 3.2.1.24), a glycoprotein with 8.6% carbohydrate was purified (26 fold purification) to homogeneity from Erythrina indica seeds, by gel filtration on Bio-Gel P-100 and affinity chromatography on Con-A CL Seralose. The enzyme had the molecular mass of 124 kDa and 127 kDa by gel filtration and SDS-PAGE, respectively. The optimum pH and temperature for enzyme activity were found to be 4.6 and 50 degrees C, respectively. The K(m) value for the enzyme was 2.1 mM for p-nitrophenyl-alpha-D-mannopyranoside. The enzyme activity was found to depend on the presence of Zn2+. Chemical modification studies revealed the involvement of tryptophan, serine and cysteine for enzyme activity.

Purification, some properties of a D-galactose-binding leaf lectin from Erythrina indica and further characterization of seed lectin.

Lectin from a leaf of Erythrina indica was isolated by affinity chromatography on Lactamyl-Seralose 4B. Lectin gave a single band in polyacrylamide gel electrophoresis (PAGE). In SDS-gel electrophoresis under reducing and non-reducing conditions Erythrina indica leaf lectin (EiLL) split into two bands with subunit molecular weights of 30 and 33 kDa, whereas 58 kDa was obtained for the intact lectin by gel filtration on Sephadex G-100. EiLL agglutinated all human RBC types, with a slight preference for the O blood group. Lectin was found to be a glycoprotein with a neutral sugar content of 9.5%. The carbohydrate specificity of lectin was directed towards D-galactose and its derivatives with pronounced preference for lactose. EiLL had pH optima at pH 7.0; above and below this pH lectin lost sugar-binding capability rapidly. Lectin showed broad temperature optima from 25 to 50 degrees C; however, at 55 degrees C EiLL lost more than 90% of its activity and at 60 degrees C it was totally inactivated. The pI of EiLL was found to be 7.6. The amino acid analysis of EiLL indicated that the lectin was rich in acidic as well as hydrophobic amino acids and totally lacked cysteine and methionine. The N-terminal amino acids were Val-Glu-Thr-IIe-Ser-Phe-Ser-Phe-Ser-Glu-Phe-Glu-Ala-Gly-Asn-Asp-X-Leu-Thr-Gln-Glu-Gly-Ala-Ala-Leu-. Chemical modification studies of both EiLL and Erythrina indica seed lectin (EiSL) with phenylglyoxal, DEP and DTNB revealed an absence of arginine, histidine and cysteine, respectively, in or near the ligand-binding site of both lectins. Modification of tyrosine with NAI led to partial inactivation of EiLL and EiSL; however, total inactivation was observed upon NBS-modification of two tryptophan residues in EiSL. Despite the apparent importance of these tryptophan residues for lectin activity they did not seem to have a direct role in binding haptenic sugar as D-galactose did not protect lectin from inactivation by NBS.