Enterococci highly resistant to penicillin: characterizing isolates from Singapore hospitals

Area of Science:

• Medical Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Enterococci are recognized as significant nosocomial pathogens.
• Increasing incidence of severe sepsis caused by enterococci in immunocompromised patients.
• Emergence of antibiotic resistance in enterococci limits treatment options.

Purpose of the Study:

• To survey the prevalence of high-level antibiotic resistance in enterococcal isolates.
• To characterize the resistance patterns of resistant enterococcal strains.
• To assess the clinical significance of highly-resistant enterococci.

Main Methods:

• Survey of 898 enterococcal isolates between September and November 1989.
• Determination of minimum inhibitory concentrations (MICs) for penicillin and ampicillin.
• Phenotypic characterization of beta-lactamase production and high-level resistance to aminoglycosides (gentamicin, streptomycin).

Main Results:

• 52 out of 898 isolates (5.8%) exhibited high-level resistance to penicillin and ampicillin (MIC > 100 mg/l).
• All resistant isolates were identified as Enterococcus faecium.
• Resistant strains did not produce beta-lactamase but showed high-level resistance to gentamicin and streptomycin.
• Most resistant isolates were from urinary tract infections; some caused bacteremia in critically ill patients.

Conclusions:

• Enterococcus faecium has acquired high-level resistance to penicillin, ampicillin, gentamicin, and streptomycin.
• These highly-resistant strains, particularly from urinary sources, represent a growing clinical concern.
• The spread of such multidrug-resistant enterococci could severely restrict therapeutic choices for systemic infections.