Investigating a Defined Minimal Medium for Systems Analyses of MDR Staphylococcus aureus

Staphylococcus aureus is a gram-positive pathogenic bacterium that has colonized an estimated one-third of the human population and such infections can often become fatal. The adaptive mechanisms of S. aureus, however, still remain obscure partially due to a lack of knowledge in its metabolic requirements. Systems biology approaches can be extremely useful in predicting and interpreting metabolic phenotypes through genome-scale modeling and bioinformatics approaches. However, there is a need for a validated chemically defined minimal medium to further investigate the requirements of the cell. Identifying the nutritional requirements will provide mechanistic insights into the functional states of the cell and its pathogenicity. In this work, a chemically defined minimal medium formulation, termed synthetic minimal medium (SMM), was investigated, modified, and validated to enable growth of three S. aureus strains, and enable systems analyses of this important pathogen. The formulated SMM was utilized in an adaptive laboratory evolution (ALE) experiment to further probe the ideal capabilities of the targeted strains and uncover mechanisms underlying the optimized states. The evolved strains were phenotypically characterized for their physiological characteristics and antimicrobial susceptibility. The genome of each strain was sequenced to examine the genetic basis for the observed phenotypes. The resulting SMM and the evolved strains will serve as important reagents for studying the resistance phenotypes of S. aureus