Effect of bile acid derivatives on taurine biosynthesis and extracellular slime production in encapsulated Staphylococcus aureus S-7

Abstract

Various bile acids were added to cultures of encapsulated strains of Staphylococcus aureus growing in serum-soft agar medium of brain heart infusion broth. We examined effects of these compounds on cellular characteristics such as growth type, cell volume index, clumping factor reaction, slime yield, taurine content, and L-(--)-cysteic acid decarboxylase activity. Upon addition to the medium of either taurochenodeoxycholic acid, taurocholic acid (25 to 50 microgram/ml), or cholic acid (10 to 25 microgram/ml), the colonial morphology of taurine-positive cells (strain S-7) was altered from the diffuse to the compact type in serum-soft agar. Also, the titer of the clumping factor reaction increased, while the cell volume index and slime yield were markedly decreased. Tauro-bile acids, including taurocholic acid, taurochenodeoxycholic acid, taurodehydrocholic acid, and taurodeoxycholic acid (50 microgram/ml) inhibited the synthesis of taurine and resulted in decreased L-(--)-cysteic acid decarboxylase activity. Among all of the derivatives cholic acid itself was found to inhibit slime production and L-(--)-cysteic acid decarboxylase activity to the greatest extent. Glyco-bile acid derivatives and taurolicholic acid (50 to 100 microgram/ml) had no effect on L-(--)-cysteic acid decarboxylase activity. Compounds such as glycodeoxycholic acid (50 to 100 microgram/ml) had no effect upon any of the cellular characteristics tested. No effect was observed upon addition of any of these compounds to cultures of the taurine-negative strain (T-26-B). We did find a correlation between the inhibition of taurine biosynthesis and decreased slime production. Electron micrographs indicated that this encapsulated strain was converted to an unencapsulated state in the presence of bile acids.

Outermost-cell-surface changes in an encapsulated strain of Staphylococcus aureus after preservation by freeze-drying

“…We have already reported that CSP is inhibited by hightemperature cultivation (13) or the addition of bile acid derivative (12,20). Loss of CSP because of freeze-drying is an important issue because it affects the maintenance of morphological stability during the preservation of microorganisms (1,8,26,29).…”

“…Microorganism. An encapsulated strain of S. aureus, S-7 (Smith diffuse), was selected for this study (18,20). Strain * Corresponding author.…”

“…Procedure for conversion experiments of freeze-dried cells in SSA. The proportion of strain S-7 that changed from a compact to a diffuse colony morphology in SSA (conversion amount) after freeze-drying was determined by a previously described method (20). S-7 organisms were cultured in brain heart infusion (BHI) medium (Difco Laboratories, Detroit, Mich.) for 16 h (late log phase) and centrifuged at 8,000 x g. They were then harvested, and 106 cells were suspended in 0.05 M phosphate buffer as controls and in two different cryoprotectant solutions (10% nonfat skim milk [Difco] and 2% honey [commercial honey from lotus-flower; Meiji Co.…”

“…The CFR and cell volume index (CVI) of the cells were determined to observe changes in surface cell morphology caused by lyophilization by a previously described method (20). The relative clumping factor titer was defined as the highest dilution of organisms which caused clumping, as described previously (20). The CVI of the organisms was determined as described below.…”

“…Quantification of CSP after freeze-drying. Surface material of strain S-7 cultures after freeze-drying was quantified by a previously described method (20). The organisms were grown at 37°C for 18 h in 5 liters of BHI medium and dialyzed against 5 volumes of distilled water overnight at 4°C.…”