Alterations in amino acid metabolism during growth by Staphylococcus aureus following exposure to H2O2 – A multifactorial approach

Abstract

Temperature and pH are known to vary in a wound site due to the immune response and subsequent healing processes. This study used a multifactorial design to examine the cellular responses of Staphylococcus aureus to hydrogen peroxide (0–100 mM) when bacteria were grown in temperatures of 37 ± 2 °C and pH 7 ± 1, conditions potentially encountered in wound sites. A centroid sample was included in the design which represented the mid-point values of all three environmental parameters (37 °C, pH 7, 50 mM H2O2). Cytoplasmic extracts and corresponding medium supernatants were analysed for amino acid composition by gas chromatography. Exposures of S. aureus to H2O2 during the inoculation process resulted in extended lag phases lasting well after the peroxide had been neutralised by the bacterium's antioxidant systems, after which the bacteria eventually resumed growth at equivalent rates to the controls. Even though the subsequent growth rates appeared normal, the cells exhibited a variant metabolic regime at the mid-exponential phase of growth as a result of the initial exposure to peroxide. The alterations in metabolism were reflected by the differential amino acid profiles measured in the cytoplasmic extracts (P < 0.0001). The data indicated that the metabolic responses to H2O2 challenge were uniquely different depending on the variations of temperature and pH. The uptake patterns of amino acids from the media also altered depending on prevailing environmental conditions. From these results, it was proposed that a specific reproducible homeostasis could be induced under a specific set of defined environmental conditions. It was also evident that early toxic insults on the bacterial culture could have lasting impacts on cellular homeostasis after successive generations, even after the offending chemical had been removed and initial cell integrity restored. It was concluded that metabolic homeostasis would be continually adjusting and responding to changing environmental conditions to deploy defensive proteins as well as optimising processes for survival. The powerful ability to continually and rapidly adapt to the environment may represent the key feature supporting the virulence of S. aureus as an opportunistic pathogen invading the wound site.

The Uptake and Release of Amino Acids by Staphylococcus aureus at Mid-Exponential and Stationary Phases and Their Corresponding Responses to Changes in Temperature, pH and Osmolality

“…Another study showed that limited proline in the media impaired staphylococcal growth and survival (Schwan et al, 2004). likewise, combinations of subtle environmental parameters led to substantial modifications in amino acid uptake profiles associated with significant patterns of cytoplasmic amino acids (Murphy et al, 2018). Similarly, significant changes in cytoplasmic amino acid compositions of S. aureus in response to variation in pH, temperature and osmotic pressure were observed (Alreshidi et al, 2016).…”

Metabolic Profiles of Clinical Strain of Staphylococcus aureus to Subtle Changes in the Environmental Parameters at Different Phases of Growth

“…Another study determined significant changes in the fatty acid composition and cell sizes of Staphylococcus lugdunensis in response to alterations in environmental conditions including changes in pH and temperature 8 . A recent study exhibited that hydrogen peroxide combined with other environmental factors such as altered pH and temperature led to very different metabolic profiles of a clinical isolate of S. aureus 10 , suggested these alterations in amino acids were essential for survival under changes in the environmental conditions. Moreover, a new study revealed that S. aureus taken up and released different levels of amino acids following growth in altered environmental conditions 29 .…”

“…Thus, it was assumed that characteristic and specific changes in the amino acid and fatty acid metabolites as well as protein composition led to the survival of S. aureus when exposed to confined nutrition in combination with higher concentrations of NaCl 9 . A recent study indicated that hydrogen peroxide (H 2 O 2 ) combined with various temperatures and pH induced alterations in the amino acid profiles of clinical isolate of S. aureus 10 .…”

Transporters and Efflux Pumps Are the Main Mechanisms Involved in Staphylococcus epidermidis Adaptation and Tolerance to Didecyldimethylammonium Chloride

“…This was shown by an analysis of the amino-acid profile of S. aureus after exposure to hydrogen peroxide [64]. Modifications to the amino-acid profile influence many biological pathways in cells, as amino acids are required for protein synthesis, and used for synthesis of the cell-wall and nucleic acids, and they can be used as energy substrates [64]. Reductions in cytoplasmic amino acids has been associated with slower rates of metabolism, to conserve energy for basal metabolism [65].…”

“…Modifications to amino acids have been shown to be a response mechanism for a changing environment. This was shown by an analysis of the amino-acid profile of S. aureus after exposure to hydrogen peroxide [64]. Modifications to the amino-acid profile influence many biological pathways in cells, as amino acids are required for protein synthesis, and used for synthesis of the cell-wall and nucleic acids, and they can be used as energy substrates [64].…”