Skip directly to site content Skip directly to page options Skip directly to A-Z link Skip directly to A-Z link Skip directly to A-Z link
Volume 5, Number 6—December 1999

Proficiency in Detecting Vancomycin Resistance in Enterococci among Clinical Laboratories in Santiago, Chile

On This Page
Article Metrics

Cite This Article

To the Editor: Vancomycin-resistant enterococci (VRE) can be difficult to detect because of limitations in the susceptibility testing methods commonly used in clinical laboratories. Although VRE have not been reported in Chile, clinical isolates have been reported in Argentina (1) and Brazil (2). It is important to detect vancomycin resistance as early as possible, so infection control preventive measures can be instituted when they have their greatest impact. The microbiology laboratory is the first line of defense against VRE, as it plays a critical role in its recognition. In Chile, most laboratories follow the National Committee for Clinical Laboratory Standards recommendations for antimicrobial susceptibility testing and use disk-diffusion methods (3); however, these methods have limitations in detecting low levels of resistance to vancomycin in enterococci.

We evaluated the ability of referral microbiology laboratories in Chile to detect vancomycin resistance in five Enteroccocus spp. isolates with different susceptibility patterns for vancomycin, penicillin, and ampicillin. Of six referral laboratories that agreed to participate, four used the disk-diffusion method to evaluate antimicrobial susceptibility. Two used an agar dilution minimum inhibitory concentration (MIC) method, one as the only susceptibility testing method and the other in addition to disk diffusion. The participants correctly evaluated vancomycin susceptibility in 17 (57%) of 30 isolates.

The accuracy of detecting vancomycin resistance varied according to the level of resistance. Isolate 1, which had a high level of resistance (Van A phenotype, MIC 256 µg/ml), was evaluated correctly in 5 (83%) of 6 laboratories. Isolate 2, with a lower level of resistance (Van B, MIC 64 µg/ml), was evaluated correctly in 4 (67%) of 6 laboratories. Isolates 3 and 4, both with intermediate resistance (Van B, MIC 16-32 µg/ml, and Van C, MIC 8 µg/ml, respectively), were evaluated correctly by one laboratory each. Isolate 5 (vancomycin susceptible) was evaluated correctly by all laboratories. Susceptibility to penicillin and ampicillin was correctly identified in 53 (96.4%) of 55 isolates. Although laboratories correctly identified E. faecium and E. faecalis to the species level, most (4 of 5) did not correctly identify E. gallinarum (three misidentified it as E. casseliflavus and one as E. faecalis).

The results of this study are consistent with those of previous studies in the United States (4,5), South America (6), Spain (7), and Mexico (8). Although in countries like Chile, disk diffusion is practical and reliable for most susceptibility testing, detecting low-level vancomycin resistance in enterocci is difficult without supplementary testing. In Chile, as in other countries, strategies should be implemented to improve detection of these strains, including improvement of phenotypical and genotypical methods for VRE detection and species identification. Documentation of proficiency in detecting VRE is important for improving laboratory performance, detecting clinical isolates, and accurate and reliable reporting to local, national, and international surveillance systems.


Jaime A. Labarca*, L. Clifford McDonald†, María Eugenia Pinto‡, Elizabeth Palavecino*‡, Patricia González‡, Erna Cona‡, Alejandra Fernández‡, María Soledad Giglio‡, and William R. Jarvis†
Author affiliations: *P. Universidad Católica de Chile, Santiago, Chile; †Centers for Disease Control and Prevention, Atlanta, Georgia, USA; and ‡Chilean Society for Infectious Diseases, Santiago, Chile



  1. Marin  ME, Mera  JR, Arduino  RC, Correa  AP, Coque  TM, Stambulian  D, First report of vancomycin-resistant Enterococcus faecium isolated in Argentina. Clin Infect Dis. 1998;26:2356. DOIPubMedGoogle Scholar
  2. Cereda  RF, Medeiros  EA, Vinagre  A, Rego  ST, Hashimoto  A, Febre  N, Epidemiologic analysis for acquisition of vancomycin-resistant enterococcus (VRE) in an intensive care unit in Brazil. In: Proceedings of the Eighth Annual Meeting of the Society for Healthcare Epidemiology of America; 1998; São Paulo, Brazil.
  3. National Committee for Clinical Laboratory Standards (NCCLS). Performance standards for antimicrobial disk susceptibility tests: approved standard M2-A6, 6th ed. Villanova (PA): The Committee.
  4. Tenover  FC, Tokars  J, Swenson  J, Paul  S, Spitalny  K, Jarvis  WR. Ability of clinical laboratories to detect antimicrobial agent-resistant enterococci. J Clin Microbiol. 1993;31:16959.PubMedGoogle Scholar
  5. Rosenberg  J, Tenover  FC, Wong  J, Jarvis  W, Vugia  DJ. Are clinical laboratories in California accurately reporting vancomycin-resistant enterococci? J Clin Microbiol. 1997;35:252630.PubMedGoogle Scholar
  6. Cookson  ST, Lopardo  H, Marin  M, Arduino  R, Rial  MJ, Altschuler  M, Study to determine the ability of clinical laboratories to detect antimicrobial-resistant Enterococcus spp. in Buenos Aires, Argentina. Diagn Microbiol Infect Dis. 1997;29:1079. DOIPubMedGoogle Scholar
  7. Alonso-Echanove  J, Robles  B, Jarvis  WR. Proficiency of clinical laboratories in Spain in detecting vancomycin-resistant Enterococcus spp. The Spanish VRE Study Group. J Clin Microbiol. 1999;37:214852.PubMedGoogle Scholar
  8. McDonald  LC, Garza  LR, Jarvis  WR. Proficiency of clinical laboratories in and near Monterrey, Mexico, to detect vancomycin-resistant enterococci. Emerg Infect Dis. 1999;5:1436. DOIPubMedGoogle Scholar


Cite This Article

DOI: 10.3201/eid0506.990623

Related Links


Table of Contents – Volume 5, Number 6—December 1999

Page created: December 16, 2010
Page updated: December 16, 2010
Page reviewed: December 16, 2010
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.