title: MurAA is required for intrinsic cephalosporin resistance of Enterococcus faecalis.
abstract: Enterococcus faecalis is a low-GC Gram-positive bacterium that is intrinsically resistant to cephalosporins, antibiotics that target cell wall biosynthesis. To probe the mechanistic basis for intrinsic resistance, a library of transposon mutants was screened to identify E. faecalis strains that are highly susceptible to ceftriaxone, revealing a transposon mutant with a disruption in murAA. murAA is predicted to encode a UDP-N-acetylglucosamine 1-carboxyvinyl transferase that catalyzes the first committed step in peptidoglycan synthesis: phosphoenolpyruvate (PEP)-dependent conversion of UDP-N-acetylglucosamine to UDP-N-acetylglucosamine-enolpyruvate. In-frame deletion of murAA, but not its homolog in the E. faecalis genome (murAB), led to increased susceptibility of E. faecalis to cephalosporins. Furthermore, expression of murAA enhanced cephalosporin resistance in an E. faecalis mutant lacking IreK (formerly PrkC), a key kinase required for cephalosporin resistance. Further genetic analysis revealed that MurAA catalytic activity is necessary but not sufficient for this role. Collectively, our data indicate that MurAA and MurAB have distinct roles in E. faecalis physiology and suggest that MurAA possesses a unique property or activity that enables it to enhance intrinsic resistance of E. faecalis to cephalosporins.
authors.affiliation: Department of Microbiology and Molecular Genetics, Center for Infectious Disease Research, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
authors.forename: Dušanka
authors.initials: D
authors.lastname: Vesić
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Kristich
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002443:Ceftriaxone / Q000494:pharmacology*; D018550:Cephalosporin Resistance / Q000187:drug effects / Q000235:genetics*; D004251:DNA Transposable Elements; D013293:Enterococcus faecalis / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D004926:Escherichia coli; D017353:Gene Deletion; D016908:Gram-Positive Bacterial Infections / Q000188:drug therapy / Q000382:microbiology; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D009154:Mutation; D010770:Phosphotransferases / Q000235:genetics* / Q000378:metabolism; D010957:Plasmids; D014169:Transformation, Bacterial
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D007527:Isoenzymes; D002443:Ceftriaxone; D019883:Alkyl and Aryl Transferases; C022566:UDP-N-acetylglucosamine 1-carboxyvinyltransferase; D010770:Phosphotransferases