Human Serum Alters the Metabolism and Antibiotic Susceptibility of .

is a common source of hospital-acquired bacterial infections, where the emergence of antibiotic resistance is a serious human health concern. Most investigations into virulence and antibiotic resistance have relied on cultivation conditions and optimized media formulations. However, can survive and adapt to a hostile host environment or antibiotic treatments by rapidly adjusting its metabolic activity. To assess this metabolic response, strains susceptible and nonsusceptible to daptomycin were cultivated in medium supplemented with 55% serum to more closely approximate conditions. Growth analyses, MIC testing, and NMR-based metabolomics determined that serum decreased daptomycin susceptibility and altered metabolism in . Both strains exhibited altered amino acid biosynthesis and catabolism, enhanced fermentation, and a modified salt tolerance response. The observation that growth conditions defined to antibiotics by may be a critical consideration for designing an effective drug discovery study.