Correlation between the essential amino-acid requirements of Staphylococcus aureus, their phage types and antibiotic patterns

Modeling of stringent-response reflects nutrient stress induced growth impairment and essential amino acids in different Staphylococcus aureus mutants

Stapylococcus aureus colonises the nose of healthy individuals but can also cause a wide range of infections. Amino acid (AA) synthesis and their availability is crucial to adapt to conditions encountered in vivo. Most S. aureus genomes comprise all genes required for AA biosynthesis. Nevertheless, different strains require specific sets of AAs for growth. In this study we show that regulation inactivates pathways under certain conditions which result in these observed auxotrophies. We analyzed in vitro and modeled in silico in a Boolean semiquantitative model (195 nodes, 320 edges) the regulatory impact of stringent response (SR) on AA requirement in S. aureus HG001 (wild-type) and in mutant strains lacking the metabolic regulators RSH, CodY and CcpA, respectively. Growth in medium lacking single AAs was analyzed. Results correlated qualitatively to the in silico predictions of the final model in 92% and quantitatively in 81%. Remaining gaps in our knowledge are evaluated and discussed. This in silico model is made fully available and explains how integration of different inputs is achieved in SR and AA metabolism of S. aureus. The in vitro data and in silico modeling stress the role of SR and central regulators such as CodY for AA metabolisms in S. aureus.

Effects of binding and bactericidal action of vancomycin on Bacillus licheniformis cell wall organization as probed by 15N nuclear magnetic resonance spectroscopy

The effects of binding and the bactericidal action of vancomycin on the arrangement and mobilities of cell wall polymers in Bacillus licheniformis were investigated by (15)N nuclear magnetic resonance spectroscopy. The bactericidal action of vancomycin led to reduced mobilities of cell wall teichoic acid and teichuronic acid in surviving cells. The decrease in teichoic acid mobility was also observed upon binding of vancomycin to B. licheniformis cells and resulted from a specific interaction between the antibiotic and teichoic acid, rather than from electrostatic contraction of the cell wall. The reduction in teichuronic acid mobility appeared to be related either to the elastic contraction of the cell wall resulting from loss of cell turgor or to separation of the cell wall from the protoplast membrane. No spectral changes associated with cell wall autolysis or alterations in cell wall composition, amidation, and cross-linking were found in vancomycin-treated B. licheniformis cells. Binding of vancomycin to Micrococcus lysodeikticus cell walls led to a decrease in mobility of C-terminal d-alanine residues but was accompanied by an increase in the mobilities of other peptidoglycan residues. The possible contributions of changes in the arrangements of cell wall polymers to the lethal action of vancomycin is discussed.

[Utilization of inorganic sulfur sources by Staphylococcus aureus strains]

Staphylococcus aureus strains of different host-adapted variants (Meyer 1966) have been tested for their ability to use inorganic sulfur sources. All the 25 strains tested were able to utilize sodium sulfide as sulfur source in a medium similar to that described by Kloos and Pattee (1965). Using S. aureus strain 116/74 grown in a medium containing Na2-35S as the only sulfur source we studied incorporation and insertion of inorganic sulfide into sulfur containing amino acids. In disintegrated and fractionated cellular material we could find 35S labelled homocystine and methionine as major compounds, and cystine, cysteic acid, homocysteic acid, and beta-sulphopyruvate as minor compounds. The occurrence of homocystine and the sulfonic acids in bacterial proteins is rather uncommon.

EFFECT OF DIET AND STRAIN DIFFERENCE ON THE VIRULENCE OF STAPHYLOCOCCUS AUREUS FOR MICE

Years of intensive investigations in our laboratories on staphylococcal infections in mice have indicated a gradual decrease in the virulence of Staphylococcus aureus for this animal, particularly the strain we were using, the random-bred BT mouse. The present investigations, based on changes in diet and strain differences in mice, were undertaken in an attempt to improve susceptibility of our stock strain, on the one hand, and to determine whether susceptibility was influenced by genetic strain differences, on the other. In the first series of experiments, littermate mice of the BT strain were placed on different diets: one group received a commercial diet; the other, a basic diet previously established in our laboratories as adequate for growth requirements of the animals. An increase in the susceptibility of the animals to staphylococcal infection was noted in the mice receiving the basic diet. In the second series of investigations, three other strains of mice (the Swiss albino, the C3H/HeJ, and the C57B1) previously not used by our laboratories in staphylococcal experiments were studied for staphylococcal susceptibility. These experiments revealed that all of these strains of mice were highly susceptible to the infection, even though they were maintained on a commercial diet.