Search

The mode of action of aqueous garlic extract (AGE) was studied in Candida albicans. The minimum inhibitory concentration (MIC) of AGE against six clinical yeast isolates ranged between 0.8 and 1.6 mg ml-1. Scanning electron microscopy and cell leakage studies showed that garlic treatment affected the structure and integrity of the outer surface of the yeast cells. Growth of C. albicans in the presence of AGE affected the yeast lipid in a number of ways: the total lipid content was decreased; garlic-grown yeasts had a higher level of phosphatidylserines and a lower level of phosphatidylcholines; in addition to free sterols and sterol esters, C. albicans accumulated esterified steryl glycosides; the concentration of palmitic acid (16:0) and oleic acid (18:1) increased and that of linoleic acid (18:2) and linolenic acid (18:3) decreased. Oxygen consumption of AGE-treated C. albicans was also reduced. The anticandidal activity of AGE was antagonized by thiols such as L-cysteine, glutathione and 2-mercaptoethanol. Interaction studies between AGE and thiols included growth antagonism, enzymic inhibition and interference of two linear zones of inhibition. All three approaches suggest that AGE exerts its effect by the oxidation of thiol groups present in the essential proteins, causing inactivation of enzymes and subsequent microbial growth inhibition.

The mode of action of the antimicrobial agent, 5-bromo-5-nitro-1,3-dioxane (bronidox), was studied in detail for gram-positive and gram-negative bacteria, yeast and fungi. The studies included MIC testing, thiol inhibition of activity, intracellular leakage, oxygen consumption, incorporation of 3H-uridine, scanning electron microscopy, inhibition of enzyme activity (papain) and in vitro oxidation of thiols to disulfides. It appears that the primary mode of action of bronidox is the same as, or similar to, that of bronopol, i.e. the oxidation of essential protein thiol causing inhibition of enzyme activity and subsequent inhibition of microbial growth.

The minimum inhibitory concentration values for a group of synthesized heterocyclic systems were determined for Gram-positive and Gram-negative bacteria, yeast and fungi. The active compounds were screened further against a number of yeast and yeast-like organisms and Gram-positive bacteria. The effect of two of these compounds on growth and mutagenicity was also tested. An attempt was made to correlate the structure of the compounds with their antimicrobial activity.

Candida albicans grown in dexamethasone (DXM) shows an apparent increase in dry weight. This increase, however, represents an artefact due to entrapment and incorporation of DXM by the yeast. Thus opportunistic infections by C. albicans which are promoted by DXM must be due entirely to effects other than growth enhancement of the organism.

The minimum inhibitory concentration values for a group of synthesized heterocyclic derivatives of 1-methyl-1-nitroethyl sulphide were determined for Gram-positive and Gram-negative bacteria, yeast, and fungi. The active compounds were further screened. The effect of these compounds on growth, morphology and incorporation of 3H-uridine was also tested. Comments on the possible model of action of such compounds is included.

Lipids extracted from Candida albicans and C. tropicalis, but not from the weakly adherent C. pseudotropicalis, significantly blocked in vitro adherence of the respective yeast cells to buccal epithelial cells. The percentage of reduction from control values ranged between 16.4 and 42.1%, depending on the species, the strain, and the solvent used for lipid extraction. The constituent lipid classes of both the acetone and chloroform-methanol extracts of C. albicans ATCC 10231 were qualitatively and quantitatively analyzed. The individual classes were isolated by preparative thin-layer chromatography and then tested for their effects on the adherence of this strain to buccal epithelial cells. Individual phospholipids, sterols, and steryl esters blocked adherence significantly (between 15.5 and 55.7% reduction). Triacylglycerols and free fatty acids showed no effect whatsoever. The same results were obtained when standard lipid samples were investigated.

The minimum inhibitory concentration values against Gram-negative and Gram-positive bacteria were determined and compared for a selected group of synthesized alpha-substituted 2-methyl-5-nitrofuran derivatives. In vitro oxidation of thiols to disulfides by 2-(iodomethyl)-5-nitrofuran indicated that oxidation of enzyme-thiol groups to disulfide bonds was a possible mode of action; but was discounted by noninhibition of thiol enzymes by these compounds. Electron-microscopic studies of the morphology of bacteria after treatment with these derivatives showed the formation of unusual elongation, branching and atypical rod shapes in E. coli, while S. aureus manifested multibud formation with some cytoplasmic protrusions. The possible mode of action of these compounds is discussed.