Alpha-toxin of Staphylococcus aureus.

Alpha-toxin, the major cytotoxic agent elaborated by Staphylococcus aureus, was the first bacterial exotoxin to be identified as a pore former. The protein is secreted as a single-chain, water-soluble molecule of Mr 33,000. At low concentrations (less than 100 nM), the toxin binds to as yet unidentified, high-affinity acceptor sites that have been detected on a variety of cells including rabbit erythrocytes, human platelets, monocytes and endothelial cells. At high concentrations, the toxin additionally binds via nonspecific absorption to lipid bilayers; it can thus damage both cells lacking significant numbers of the acceptor and protein-free artificial lipid bilayers. Membrane damage occurs in both cases after membrane-bound toxin molecules collide via lateral diffusion to form ring-structured hexamers. The latter insert spontaneously into the lipid bilayer to form discrete transmembrane pores of effective diameter 1 to 2 nm. A hypothetical model is advanced in which the pore is lined by amphiphilic beta-sheets, one surface of which interacts with lipids whereas the other repels apolar membrane constitutents to force open an aqueous passage. The detrimental effects of alpha-toxin are due not only to the death of susceptible targets, but also to the presence of secondary cellular reactions that can be triggered via Ca2+ influx through the pores. Well-studied phenomena include the stimulation of arachidonic acid metabolism, triggering of granule exocytosis, and contractile dysfunction. Such processes cause profound long-range disturbances such as development of pulmonary edema and promotion of blood coagulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Carotenoid Formation by Staphylococcus aureus

The carotenoid pigments of Staphylococcus aureus U-71 were identified as phytoene; zeta-carotene; delta-carotene; phytofluenol; a phytofluenol-like carotenoid, rubixanthin; and three rubixanthin-like carotenoids after extraction, saponification, chromatographic separation, and determination of their absorption spectra. There was no evidence of carotenoid esters or glycoside ethers in the extract before saponification. During the aerobic growth cycle the total carotenoids increased from 45 to 1,000 nmoles per g (dry weight), with the greatest increases in the polar, hydroxylated carotenoids. During the anaerobic growth cycle, the total carotenoids increased from 20 nmoles per g (dry weight) to 80 nmoles per g (dry weight), and only traces of the polar carotenoids were formed. Light had no effect on carotenoid synthesis. About 0.14% of the mevalonate-2-(14)C added to the culture was incorporated into the carotenoids during each bacterial doubling. The total carotenoids did not lose radioactivity when grown in the absence of (14)C for 2.5 bacterial doublings. The total carotenoids did not lose radioactivity when grown in the absence of (14)C for 2.5 bacterial doublings. The incorporation and turnover of (14)C indicated the carotenes were sequentially desaturated and hydroxylated to form the polar carotenoids.     

Utilization of glycerophosphodiesters by Staphylococcus aureus

The facultative pathogen Staphylococcus aureus colonizes the human anterior nares and causes infections of various organ systems. Which carbon, energy, and phosphate sources can be utilized by S. aureus in nutrient‐poor habitats has remained largely unknown. We describe that S. aureus secretes a glycerophosphodiesterase (glycerophosphodiester phosphodiesterase, EC 3.1.4.46), GlpQ, degrading the glycerophosphodiester (GPD) head groups of phospholipids such as human phosphatidylcholine (GroPC). Deletion of glpQ completely abolished the GroPC‐degrading activity in S. aureus culture supernatants. GroPC has been detected in human tissues and body fluids probably as a result of phospholipid remodelling and degradation. Notably, GroPC promoted S. aureus growth under carbon‐ and phosphate‐limiting conditions in a GlpQ‐dependent manner indicating that GlpQ permits S. aureus to utilize GPD‐derived glycerol‐3‐phosphate as a carbon and phosphate sources. Thus, S. aureus can use a broader spectrum of nutrients than previously thought which underscores its capacity to adapt to the highly variable and nutrient‐poor surroundings.     

Restriction-deficient mutants of Staphylococcus aureus.

A series of restriction-deficient mutants was isolated from non-lysogenic strains of Staphylococcus aureus belonging to phage groups I and II. Some mutants were sensitive to all phages tested. With one possible exception, all the mutants were unaffected in their modification systems. The breakdown of DNA of phages, restricted in the parental strains, was reduced in both the mutants that were tested. The restriction in propagating strain 3A could be transduced to its restriction-deficient mutant. The transduction efficiency increased after ultraviolet irradiation of the transducing phage suggesting that the gene for restriction is present on the bacterial chromosome.     

Prevention of Staphylococcus aureus lysis.

Staphylococcus aureus S-6 cells grown in chemically defined media often lysed after exponential growth. Lysis could be prevented by the addition of alanine or proline before the culture reached stationary phase.     

Enterotoxin B formation by fermentation mutants of Staphylococcus aureus.

An appreciable fraction of carbohydrate-negative (car) mutants of Staphylococcus aureus strains ATCC 14458, 778, and S-6 exhibit increased enterotoxin B (SEB) production. In addition, some lac and mtl mutants of these strains also display enhanced SEB formation. All such mutants appear to be point mutations. Mutagen-induced reversions of high SEB producing car, mtl, or lac mutants yield varying amounts of SEB and some clones seem to be restored to the characteristics of the parent type. A few sequentially isolated lac, mtl double mutants of strain 778 elaborate much more or much less SEB than either the lac or the mtl single mutants.     

Heme coordination by Staphylococcus aureus IsdE

Staphylococcus aureus is a Gram-positive bacterial pathogen and a leading cause of hospital acquired infections. Because the free iron concentration in the human body is too low to support growth, S. aureus must acquire iron from host sources. Heme iron is the most prevalent iron reservoir in the human body and a predominant source of iron for S. aureus. The iron-regulated surface determinant (Isd) system removes heme from host heme proteins and transfers it to IsdE, the cognate substrate-binding lipoprotein of an ATP-binding cassette transporter, for import and subsequent degradation. Herein, we report the crystal structure of the soluble portion of the IsdE lipoprotein in complex with heme. The structure reveals a bi-lobed topology formed by an N- and C-terminal domain bridged by a single alpha-helix. The structure places IsdE as a member of the helical backbone metal receptor superfamily. A six-coordinate heme molecule is bound in the groove established at the domain interface, and the heme iron is coordinated in a novel fashion for heme transporters by Met(78) and His(229). Both heme propionate groups are secured by H-bonds to IsdE main chain and side chain groups. Of these residues, His(229) is essential for IsdE-mediated heme uptake by S. aureus when growth on heme as a sole iron source is measured. Multiple sequence alignments of homologues from several other Gram-positive bacteria, including the human pathogens pyogenes, Bacillus anthracis, and Listeria monocytogenes, suggest that these other systems function equivalently to S. aureus IsdE with respect to heme binding and transport.     

Staphylococcus aureus Protoplasting Induced by d-Cycloserine

Addition of sublethal doses of d-cycloserine to growing cells of Staphylococcus aureus induces the rupture of the cell wall along an equatorial ring, thus allowing the liberation of protoplasts.     

Stress resistance in Staphylococcus aureus.

Staphylococcus aureus is a major human pathogen of increasing importance as a result of the spread of antibiotic resistance. It causes a wide range of diseases and survives outside the host by virtue of its adaptability and resistance to environmental stress. Several cellular components involved in Staphylococcus aureus stress resistance have begun to be characterized.