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© Research
Publication : Antimicrobial agents and chemotherapy

Mutation landscape of acquired cross-resistance to glycopeptide and β-lactam antibiotics in Enterococcus faecium

Scientific Fields
Diseases
Organisms
Applications
Technique

Published in Antimicrobial agents and chemotherapy - 15 Jun 2015

Sacco E, Cortes M, Josseaume N, Bouchier C, Dubée V, Hugonnet JE, Mainardi JL, Rice LB, Arthur M

Link to Pubmed [PMID] – 26077262

Antimicrob. Agents Chemother. 2015 Sep;59(9):5306-15

Bypass of the d,d-transpeptidase activity of penicillin-binding proteins by an l,d-transpeptidase (Ldtfm) results in resistance to ampicillin and glycopeptides in Enterococcus faecium M9, a mutant obtained by nine consecutive selection steps. Resistance requires activation of a cryptic locus for production of the essential tetrapeptide-containing substrate of Ldtfm and impaired activity of protein phosphatase StpA. Here, whole-genome sequencing revealed a high mutation rate for the entire selection procedure (79 mutations in 900 generations). Acquisition of a mutation in the mismatch repair gene mutL had little impact on the frequency of rifampin-resistant mutants although the mutation spectrum of M9 was typical of impaired MutL with high transversion to transition (40/11) and substitution to deletion (51/28) ratios. M9 did not mainly accumulate neutral mutations since base substitutions occurred more frequently in coding sequences than expected (χ(2) = 5.0; P < 0.05) and silent mutations were underrepresented (χ(2) = 5.72; P < 0.02). None of the mutations directly affected recognition of the tetrapeptide substrate of Ldtfm by peptidoglycan synthesis enzymes. Instead, mutations appear to remodel regulatory circuits involving two-component regulatory systems and sugar metabolism. The high number of mutations required for activation of the l,d-transpeptidase pathway may strongly limit emergence of cross-resistance to ampicillin and glycopeptides by this mechanism.

http://www.ncbi.nlm.nih.gov/pubmed/26077262