ABSTRACT
A lectin isolated from the red alga Solieria filiformis was evaluated for its effect on the growth of 8 gram-negative and 3 gram-positive bacteria cultivated in liquid medium (three independent experiments/bacterium). The lectin (500 æg/mL) stimulated the growth of the gram-positive species Bacillus cereus and inhibited the growth of the gram-negative species Serratia marcescens, Salmonella typhi, Klebsiella pneumoniae, Enterobacter aerogenes, Proteus sp, and Pseudomonas aeruginosa at 1000 æg/mL but the lectin (10-1000 æg/mL) had no effect on the growth of the gram-positive bacteria Staphylococcus aureus and B. subtilis, or on the gram-negative bacteria Escherichia coli and Salmonella typhimurium. The purified lectin significantly reduced the cell density of gram-negative bacteria, although no changes in growth phases (log, exponential and of decline) were observed. It is possible that the interaction of S. filiformis lectin with the cell surface receptors of gram-negative bacteria promotes alterations in the flow of nutrients, which would explain the bacteriostatic effect. Growth stimulation of the gram-positive bacterium B. cereus was more marked in the presence of the lectin at a concentration of 1000 æg/mL. The stimulation of the growth of B. cereus was not observed when the lectin was previously incubated with mannan (125 æg/mL), its hapten. Thus, we suggest the involvement of the binding site of the lectin in this effect. The present study reports the first data on the inhibition and stimulation of pathogenic bacterial cells by marine alga lectins.
Subject(s)
Anti-Bacterial Agents/pharmacology , Rhodophyta/chemistry , Gram-Negative Bacteria/drug effects , Gram-Positive Bacteria/drug effects , Lectins/pharmacology , Anti-Bacterial Agents/isolation & purification , Gram-Negative Bacteria/cytology , Gram-Negative Bacteria/growth & development , Gram-Positive Bacteria/cytology , Gram-Positive Bacteria/growth & development , Dose-Response Relationship, Drug , Electrophoresis, Polyacrylamide Gel , Lectins/isolation & purification , Receptors, Cell SurfaceABSTRACT
The antimicrobial, hemagglutinating and toxic activities of the purple fluid of the sea hare Aplysia dactylomela are described. Intact or dialyzed purple fluid inhibited the growth of species of Gram-positive and Gram-negative bacteria and the action was not bactericidal but bacteriostatic. The active factor or factors were heat labile and sensitive to extreme pH values. The fluid preferentially agglutinated rabbit erythrocytes and, to a lesser extent, human blood cells, and this activity was inhibited by the glycoprotein fetuin, a fact suggesting the presence of a lectin. The fluid was also toxic to brine shrimp nauplii (LD 50 141.25 µg protein/ml) and to mice injected intraperitoneally (LD 50 201.8 ñ 8.6 mg protein/kg), in a dose-dependent fashion. These toxic activities were abolished when the fluid was heated. Taken together, the data suggest that the activities of the purple fluid are due primarily to substance(s) of a protein nature which may be involved in the chemical defense mechanism of this sea hare
Subject(s)
Animals , Rabbits , Mice , Aplysia , Bacteria/drug effects , Body Fluids , Hemagglutination/drug effects , Bacteria/growth & development , Electrophoresis, Polyacrylamide Gel , Growth Inhibitors , Microbial Sensitivity TestsABSTRACT
Analisaram-se a etiologia e as características clínicas da doença-diarréica em 161 lactentes pertencentes a famílias de baixas condiçöes sócio-econômicas na cidade de Recife. O estudo foi realizado no Hospital Geral de Pediatria do Instituto Materno Infantil de Pernambuco. Acompanhou-se a evoluçäo clínica do quadro diarréico de 128 lactentes. Conclue-se que a doença diarréica é predominantemente de etiologia bacteriana no grupo estudado