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pH modulation of aminoglycoside resistance in Staphylococcus epidermidis harbouring 6'-N-aminoglycoside

E Culebras1, J L Martínez, F Baquero

  • 1Centro Nacional de Biotecnología,(CSIC), Cantoblanco, Madrid, Spain.

The Journal of Antimicrobial Chemotherapy
|May 1, 1996
PubMed

Insights

The enzyme AAC(6’)IV activity varies with aminoglycoside structure and pH. Glucosamine antibiotics show pH-dependent inhibition, unlike garosamine compounds, impacting bacterial resistance.

Area of Science:

  • Microbiology
  • Enzymology
  • Pharmacology

Background:

  • Aminoglycoside antibiotics are crucial for treating bacterial infections.
  • Enzymatic modification is a key mechanism of aminoglycoside resistance.
  • The enzyme 6'-N-aminoglycoside acetyltransferase (AAC(6')IV) confers resistance by acetylating aminoglycosides.

Purpose of the Study:

  • To investigate the kinetic properties of AAC(6')IV from Staphylococcus epidermidis RYC 13036.
  • To determine how substrate structure (aminosugar moiety) and pH affect enzyme activity and inhibition.
  • To correlate enzyme kinetics with observed minimum inhibitory concentrations (MICs) of aminoglycosides.

Main Methods:

  • Enzyme kinetics assays using tobramycin, amikacin, gentamicin, and netilmicin as substrates.
  • Measurement of kinetic constants (e.g., Km, Vmax) under varying pH conditions.
  • Determination of substrate inhibition patterns and their pH dependence.

Main Results:

  • AAC(6')IV exhibited different kinetic constants for glucosamine-containing (tobramycin, amikacin) versus garosamine-containing (gentamicin, netilmicin) aminoglycosides.
  • Glucosamine acetylation was highly susceptible to substrate inhibition, which increased with pH.
  • Garosamine acetylation showed limited substrate inhibition across a broad pH range.
  • Observed kinetic differences correlated with the MIC values of S. epidermidis RYC 13036 against these aminoglycosides.

Conclusions:

  • The aminosugar moiety of aminoglycosides and environmental pH significantly influence AAC(6')IV-substrate interactions.
  • These factors modulate enzyme activity and contribute to the varying efficacy of aminoglycosides against S. epidermidis.
  • Understanding these interactions is vital for predicting and overcoming aminoglycoside resistance.

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