Abstract
Background: Staphylococcus aureus is highly associated with nosocomial infections due to its ability to adapt to wide range of environmental parameters. The aim of this study was to evaluate amino acids consumption and secretion by S. aureus at mid-exponential and stationary phases under growth in suboptimal conditions, including changes in pH, temperature and osmolality.
Methods: The consumption and secretion of amino acids were determined by subtracting the original concentrations of the free amino acids in the media from those estimated at both mid-exponential and stationary phases of growth.
Results: The analysis revealed that the consumption and secretion profiles were substantially different between cells grown under optimal control conditions, when compared with those exposed to sub-optimal conditions. The analyses of the supernatants harvested at mid-exponential phase revealed that the total consumption of amino acids was increased by 1.2 and 1.7 times by cells grown at either pH 6 or 8 and 35 degrees C with additional of 5 % NaCl, respectively. However, the final levels of amino acids consumed at stationary phase were significantly reduced in the cells grown in sub-optimal conditions compared with bacteria cells grown under optimal conditions.
Conclusion: It was evident that various environmental conditions led to differential profiles of amino acid consumption and secretion.