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Impact of specific pbp5 mutations on expression of beta-lactam resistance in Enterococcus faecium

Louis B Rice1, Samuel Bellais, Lenore L Carias

  • 1Medical and Research Services, Louis Stokes Cleveland VA Medical Center, Cleveland, Ohio 44106, USA. louis.rice@med.va.gov

Antimicrobial Agents and Chemotherapy
|July 27, 2004
PubMed

Insights

Individual mutations in penicillin-binding protein 5 (PBP 5) confer modest ampicillin resistance in Enterococcus faecium. Combinations of PBP 5 mutations, particularly at positions 485 and 466, significantly amplify resistance to beta-lactams.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Antimicrobial Resistance

Background:

  • Penicillin-binding proteins (PBPs) are essential bacterial enzymes involved in cell wall synthesis.
  • Enterococcus faecium is a significant opportunistic pathogen, often exhibiting resistance to beta-lactam antibiotics.
  • PBP 5 is a key determinant of beta-lactam resistance in E. faecium.

Purpose of the Study:

  • To investigate the impact of individual and combined PBP 5 mutations on ampicillin resistance.
  • To determine the contribution of specific PBP 5 substitutions to the expression of resistance.
  • To correlate PBP 5 mutations with penicillin affinity and beta-lactam minimum inhibitory concentrations (MICs).

Main Methods:

  • Utilized a shuttle plasmid system for expressing cloned pbp5 genes in ampicillin-susceptible E. faecium.
  • Introduced specific point mutations and insertions into the pbp5 gene.
  • Assessed ampicillin resistance levels and determined beta-lactam MICs for engineered E. faecium strains.
  • Measured penicillin affinity for wild-type and mutant PBP 5 enzymes.

Main Results:

  • Single point mutations implicated in clinical resistance conferred only modest resistance levels.
  • Combination of mutations, notably M485A and S466 insertion, resulted in the highest resistance to all beta-lactams.
  • Penicillin affinity generally correlated with beta-lactam MICs, but the relationship was not strictly proportional.

Conclusions:

  • PBP 5 mutations are critical for ampicillin resistance in E. faecium.
  • Synergistic effects of combined PBP 5 mutations significantly enhance beta-lactam resistance.
  • Understanding these mutations provides insights into mechanisms of antimicrobial resistance and potential therapeutic targets.

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