AsrR Is an Oxidative Stress Sensing Regulator Modulating Enterococcus faecium Opportunistic Traits, Antimicrobial Resistance, and Pathogenicity

Abstract

Oxidative stress serves as an important host/environmental signal that triggers a wide range of responses in microorganisms. Here, we identified an oxidative stress sensor and response regulator in the important multidrug-resistant nosocomial pathogen Enterococcus faecium belonging to the MarR family and called AsrR (antibiotic and stress response regulator). The AsrR regulator used cysteine oxidation to sense the hydrogen peroxide which results in its dissociation to promoter DNA. Transcriptome analysis showed that the AsrR regulon was composed of 181 genes, including representing functionally diverse groups involved in pathogenesis, antibiotic and antimicrobial peptide resistance, oxidative stress, and adaptive responses. Consistent with the upregulated expression of the pbp5 gene, encoding a low-affinity penicillin-binding protein, the asrR null mutant was found to be more resistant to β-lactam antibiotics. Deletion of asrR markedly decreased the bactericidal activity of ampicillin and vancomycin, which are both commonly used to treat infections due to enterococci, and also led to over-expression of two major adhesins, acm and ecbA, which resulted in enhanced in vitro adhesion to human intestinal cells. Additional pathogenic traits were also reinforced in the asrR null mutant including greater capacity than the parental strain to form biofilm in vitro and greater persistance in Galleria mellonella colonization and mouse systemic infection models. Despite overexpression of oxidative stress-response genes, deletion of asrR was associated with a decreased oxidative stress resistance in vitro, which correlated with a reduced resistance to phagocytic killing by murine macrophages. Interestingly, both strains showed similar amounts of intracellular reactive oxygen species. Finally, we observed a mutator phenotype and enhanced DNA transfer frequencies in the asrR deleted strain. These data indicate that AsrR plays a major role in antimicrobial resistance and adaptation for survival within the host, thereby contributes importantly to the opportunistic traits of E. faecium.

Nonclinical and Clinical Enterococcus faecium Strains, but Not Enterococcus faecalis Strains, Have Distinct Structural and Functional Genomic Features

“…A recent study showed that AsrR-mediated sensing of oxidative stress by Enterococcus influenced levels of antibiotic resistance, interactions with host cells, and virulence (34). Because the mucus layer is exposed to oxygen diffused from the bloodstream and intestinal epithelial cells (35), E. faecium cells might need mechanisms to tolerate oxygen in the intestine.…”

Genomic Analysis of Reduced Susceptibility to Tigecycline in Enterococcus faecium

“…Construction of deletion mutants. For the construction of the ⌬efau004_01228 strain and in an attempt to delete the efau004_00094 gene, allelic replacements were carried out as previously described (19). Briefly, DNA fragments (obtained by PCR with the chromosomal DNA of E. faecium Aus0004 as the template) containing ligated upstream and downstream sequences of the desired deletion fragment were cloned into the thermosensitive replication plasmid pWS3 (20) (Table 1), and 1 g of recombinant plasmid was used to transform E. faecium Aus0004 competent cells by electroporation.…”

Stress Physiology of Lactic Acid Bacteria

“…The deletion mutant was also susceptible to killing in murine macrophages and was less efficient at colonization and dissemination in a murine peritonitis model. AsrR (antibiotic and stress response regulator), an oxidative sensing regulator of the MarR family, was recently described for E. faecium (536). The AsrR regulon consists of genes involved in pathogenesis, antibiotic resistance, oxidative stress, and adaptive responses.…”