Exposure of clinical MRSA heterogeneous strains to β-lactams redirects metabolism to optimize energy production through the TCA cycle

• Published in: PloS one Vol. 8; no. 8; p. e71025
• Main Authors: Keaton, Mignon A, Rosato, Roberto R, Plata, Konrad B, Singh, Christopher R, Rosato, Adriana E
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 05.08.2013; Public Library of Science (PLoS)
• Subjects: Aconitate Hydratase - genetics; Adaptation; Amides; Amino Acids - metabolism; Anti-Bacterial Agents - pharmacology; Antibiotic resistance; Antibiotics; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; beta-Lactam Resistance; Biology; Carbohydrate Metabolism; Cell Membrane - metabolism; Cell survival; Cell Wall - metabolism; Cell walls; Chromatography; Citric acid; Citric Acid Cycle; Combinatorial analysis; Communities; Deactivation; Dehydrogenases; DNA Damage; DNA microarrays; DNA, Bacterial - genetics; Drug resistance; Energy Metabolism; Gas chromatography; Gene expression; Health care; Inactivation; Infections; Infectious diseases; Intermediates; Liquid chromatography; Mass spectrometry; Mass spectroscopy; Medicine; Metabolic pathways; Metabolism; Methicillin; Methicillin-Resistant Staphylococcus aureus - drug effects; Methicillin-Resistant Staphylococcus aureus - metabolism; Microbial Sensitivity Tests; Oxacillin; Oxacillin - pharmacology; Pathology; Pathways; Penicillin; Physiology; RecA protein; RNA, Bacterial - genetics; RNA, Bacterial - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; Scientific imaging; SOS response; Spectroscopy; Staphylococcus aureus; Staphylococcus infections; Studies; Transcriptome; Tricarboxylic acid cycle; β-Lactam antibiotics; United States > US; Texas
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0071025

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as one of the most important pathogens both in health care and community-onset infections. The prerequisite for methicillin resistance is mecA, which encodes a β-lactam-insensitive penicillin binding protein PBP2a. A characteristic of MRSA strains from hospital and community associated infections is their heterogeneous expression of resistance to β-lactam (HeR) in which only a small portion (≤ 0.1%) of the population expresses resistance to oxacillin (OXA) ≥ 10 µg/ml, while in other isolates, most of the population expresses resistance to a high level (homotypic resistance, HoR). The mechanism associated with heterogeneous expression requires both increase expression of mecA and a mutational event that involved the triggering of a β-lactam-mediated SOS response and related lexA and recA genes. In the present study we investigated the cellular physiology of HeR-MRSA strains during the process of β-lactam-mediated HeR/HoR selection at sub-inhibitory concentrations by using a combinatorial approach of microarray analyses and global biochemical profiling employing gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS) to investigate changes in metabolic pathways and the metabolome associated with β-lactam-mediated HeR/HoR selection in clinically relevant heterogeneous MRSA. We found unique features present in the oxacillin-selected SA13011-HoR derivative when compared to the corresponding SA13011-HeR parental strain that included significant increases in tricarboxyl citric acid (TCA) cycle intermediates and a concomitant decrease in fermentative pathways. Inactivation of the TCA cycle enzyme cis-aconitase gene in the SA13011-HeR strain abolished β-lactam-mediated HeR/HoR selection demonstrating the significance of altered TCA cycle activity during the HeR/HoR selection. These results provide evidence of both the metabolic cost and the adaptation that HeR-MRSA clinical strains undergo when exposed to β-lactam pressure, indicating that the energy production is redirected to supply the cell wall synthesis/metabolism, which in turn contributes to the survival response in the presence of β-lactam antibiotics.