Comparison of simple and rapid methods for identifying enterococci intrinsically resistant to vancomycin

Area of Science:

• Clinical microbiology
• Bacteriology
• Antimicrobial resistance

Background:

• Enterococcus species are significant human pathogens.
• Distinguishing intrinsically vancomycin-resistant enterococci (IVRE) from other Enterococcus species is crucial for effective treatment.
• Accurate and rapid identification methods are needed in clinical settings.

Purpose of the Study:

• To evaluate three methodologies for differentiating IVRE (Enterococcus casseliflavus and Enterococcus gallinarum) from Enterococcus faecalis and Enterococcus faecium.
• To identify the most reliable biochemical test for IVRE identification.

Main Methods:

• Evaluation of litmus milk (LM) reduction, arabinose (ARA) acidification, methyl-alpha-D-glucopyranoside (MGP) acidification, and rapid motility (RM) tests.
• Testing of 33 Enterococcus faecalis, 53 Enterococcus faecium, and 46 IVRE isolates.
• Comparison of test results for accurate species differentiation.

Main Results:

• Enterococcus faecalis reduced LM within 4 hours and was negative in other tests.
• Enterococcus faecium isolates were positive only for ARA.
• 98% of IVRE isolates acidified MGP, 89% were positive for LM and ARA, and 98% were RM positive.
• MGP acidification was the most sensitive single test for differentiating IVRE.

Conclusions:

• Acidification of MGP is the most useful single test for differentiating IVRE from vancomycin-resistant Enterococcus faecium and Enterococcus faecalis.
• A combination of LM-ARA and RM testing allows for accurate identification without overnight incubation.
• These rapid tests can aid in the clinical management of enterococcal infections.