The glycopeptide antibiotic vancomycin is considered indispensable for the treatment of multidrug-resistant Staphylococcus aureus infections, and so the acquisition by these organisms of transmissible glycopeptide resistance elements from enterococci had been anticipated with apprehension. It was therefore a considerable surprise when vancomycin-intermediate S. aureus (VISA) clinical isolates were reported in 1997, with a novel, borderline-resistance phenotype acquired without genetic exchange. Clinical vancomycin-resistant S. aureus (VRSA) were not reported until 2002, expressing high level, transmissible resistance by virtue of vanA resistance determinants within enterococcal transposable elements residing on staphylococcal plasmids. This review will provide an update on the frustratingly variable characteristics of the VISA phenotype, focus on the progress made in understanding the molecular basis of the VISA resistance mechanism from the viewpoint of genetic regulation and cell wall stress response, and summarize the information currently available on VRSA. Finally, alternatives to vancomycin that are already available or nearing approval will be briefly reviewed, with attention to their limitations and potential for resistance development.
A specific, Na+-dependent, energy-requiring transport system for taurine has been reported recently in the Staphylococcus aureus M strain. Taurine was taken up vigorously by all S . aureus strains tested. The system was Na+-dependent, and Na+ decreased the K , but had no effect on the V,,, of the transport system. Among coagulase-negative staphylococci, the Staphylococcus epidermidis group (a taxonomically related group of species associated with humans or other primates) and the free-living, wide-ranging species Staphylococcus sciuri showed vigorous taurine uptake. Somewhat lower rates were found in the Staphylococcus saprophyticus group. Low or barely detectable uptake rates were noted in other staphylococcal species that were primarily of animal origin. N o taurine uptake was detected in a variety of other bacterial species tested. Taurine uptake, which was not Na+-dependent, occurred in a Pseudomonas aeruginosa strain grown on taurine as sole energy, carbon, nitrogen, and sulphur source, but not when it was grown in a gluconate/salts medium. In nutritional studies we were unable to demonstrate a role for taurine as a sulphur source for S . aureus. [ 1 ,2-14C]-and [35S]taurine were taken up during overnight growth of cells, and radioactivity was distributed similarly among cellular fractions, indicating that the carbon and sulphur atoms of taurine were not cleaved and had the same fate.We were unable to demonstrate any catabolism of taurine in radiorespirometric experiments to detect evolution of I4CO2 by cells incubated with [ 1 ,2-14C]taurine. Thus, we found no evidence for a role of taurine in the energy, carbon and sulphur metabolism of S . aureus.
Fatty acids play a major role in determining membrane biophysical properties. Staphylococcus aureus produces branched-chain fatty acids (BCFAs) and straight-chain fatty acids (SCFAs), and can incorporate exogenous SCFAs and straight-chain unsaturated fatty acids (SCUFAs). Many S. aureus strains produce the triterpenoid pigment staphyloxanthin, and the balance of BCFAs, SCFAs and staphyloxanthin determines membrane fluidity. Here, we investigated the relationship of fatty acid and carotenoid production in S. aureus using a pigmented strain (Pig1), its carotenoid-deficient mutant (Pig1ΔcrtM) and the naturally non-pigmented Staphylococcus argenteus that lacks carotenoid biosynthesis genes and is closely related to S. aureus. Fatty acid compositions in all strains were similar under a given condition indicating that staphyloxanthin does not influence fatty acid composition. Strain Pig1 had decreased membrane fluidity as measured by fluorescence anisotropy than the other strains under all conditions indicating that staphyloxanthin helps maintain membrane rigidity. We could find no evidence for correlation of expression of crtM and fatty acid biosynthesis genes. Supplementation of medium with glucose increased SCFA production and decreased BCFA and staphyloxanthin production, whereas acetate-supplementation also decreased BCFAs but increased staphyloxanthin production. We believe that staphyloxanthin levels are influenced more through metabolic regulation than responding to fatty acids incorporated into the membrane.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.