Reciprocal Regulation of Cephalosporin Resistance in Enterococcus faecalis

Abstract

Antibiotic-resistant enterococci are major causes of hospital-acquired infections and therefore represent a serious public health problem. One well-known risk factor for the acquisition of hospital-acquired enterococcal infections is prior therapy with broad-spectrum cephalosporin antibiotics. Enterococci can proliferate in patients undergoing cephalosporin therapy due to intrinsic cephalosporin resistance, a characteristic of the genus Enterococcus. However, the molecular basis for cephalosporin resistance in E. faecalis has yet to be adequately elucidated. Previously we determined that a putative Ser/Thr kinase, IreK (formerly PrkC), is required for intrinsic cephalosporin resistance in E. faecalis. Here we show that kinase activity is required for cephalosporin resistance and, further, that resistance in E. faecalis is reciprocally regulated by IreK and IreP, a PP2C-type protein phosphatase encoded immediately upstream of IreK. Mutants of two divergent lineages of E. faecalis lacking IreP exhibit remarkable hyperresistance to cephalosporins but not to antibiotics targeting other cellular processes. Further genetic analyses indicate that hyperresistance of the IreP mutant is mediated by the IreK kinase. Additionally, competition experiments reveal that hyperresistant ΔireP mutants exhibit a substantial fitness defect in the absence of antibiotics, providing an evolutionary rationale for the use of a complex signaling system to control intrinsic cephalosporin resistance. These results support a model in which IreK and IreP act antagonistically via protein phosphorylation and dephosphorylation as part of a signal transduction circuit to regulate cellular adaptation to cephalosporin-induced stress.

Strain-Specific Regulatory Role of Eukaryote-Like Serine/Threonine Phosphatase in Pneumococcal Adherence

“…The D39 genome and other strains also harbor two more serine/threonine phosphatase homologs (SPD_0539 and SPD_1061, and equivalents in others), but they do not possess any sequence similarity and lack the conserved catalytic motifs, I to XI, the hallmarks of the eukaryote-like PP2C family of phosphatases (49). Thus, the successful creation of D39⌬phpP and 6A⌬phpP mutants displaying no growth defects, as has also been reported for STP mutants derived from S. aureus N315 (6), S. pyogenes M1SF370 M1T1 5448 (1), and Enterococcus faecalis (20), emphasizes the fact that PhpP is not essential for either pneumococcal growth or survival. From these published studies and the present study, we conclude that the successful creation of STP mutants in general is due to an appropriate vectorbased deletion strategy that allows nonpolar and markerless deletion.…”

Stress Physiology of Lactic Acid Bacteria

“…The E. faecalis kinase/phosphatase pair IreK/IreP is involved in intrinsic resistance against cephalosporin, as evidenced by the fact that mutants lacking ireK exhibit cephalosporin susceptibility, whereas mutants lacking ireP are hyperresistant (112). A subsequent study suggested that IreK/IreP regulates the phosphorylation state of the IreB protein, which would control a cephalosporin resistance pathway through an undetermined mechanism (113).…”

Oxidative Stress Enhances Cephalosporin Resistance of Enterococcus faecalis through Activation of a Two-Component Signaling System

“…One important well-characterized factor that is required for cephalosporin resistance is a specialized low-affinity PBP (Pbp5) that does not get inactivated by cephalosporins and can therefore perform cross-linking of peptidoglycan to permit growth in the presence of the antibiotic (6,7). Although required, Pbp5 is not sufficient for resistance, as mutations in other loci render E. faecalis susceptible to cephalosporin by mechanisms that have not been fully worked out (8)(9)(10)(11)(12).…”