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Vancomycin resistance in Staphylococcus haemolyticus causing colonization and bloodstream infection
L A Veach1, M A Pfaller, M Barrett
1Department of Internal Medicine, University of Iowa College of Medicine, Iowa City.
Journal of Clinical Microbiology
|September 1, 1990
Summary
A strain of Staphylococcus haemolyticus developed vancomycin resistance during prolonged treatment. This highlights the risk of developing vancomycin-resistant bacteria, even with susceptible initial strains.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Increasing incidence of beta-lactam-resistant coagulase-negative staphylococci necessitates broader vancomycin use.
- Coagulase-negative staphylococci have generally maintained vancomycin susceptibility.
- Emergence of vancomycin resistance is a significant concern in healthcare settings.
Observation:
- A specific strain of Staphylococcus haemolyticus exhibited increasing vancomycin resistance.
- Initial isolates from surveillance cultures showed low vancomycin MICs (1.0–2.0 µg/ml).
- Subsequent isolates from bloodstream and tracheal aspirates displayed higher MICs (8.0–16 µg/ml) after prolonged vancomycin therapy.
Findings:
- The Staphylococcus haemolyticus strain demonstrated a shift from vancomycin susceptibility to intermediate resistance.
- In vitro studies showed further vancomycin resistance could be selected.
- Plasmid DNA analysis indicated the isolates belonged to a single, closely related strain.
Implications:
- Colonization with vancomycin-susceptible S. haemolyticus can precede nosocomial infections with resistant strains.
- Prolonged vancomycin therapy is temporally associated with the development of resistance.
- This case underscores the need for vigilant monitoring of antimicrobial susceptibility and judicious use of vancomycin.