Abstract
We evaluated the abilities of 10 commercially available antimicrobial susceptibility testing methods and four reference methods (agar dilution, broth microdilution, disk diffusion, and the agar screen plate) to classify enterococci correctly as vancomycin susceptible or resistant using 50 well-characterized strains of enterococci. There was a high level of agreement of category classification data obtained with broth-based systems (Sceptor, MicroMedia, Pasco, and Sensititre), agar dilution, and an antibiotic gradient method (E test) with data obtained by reference broth microdilution; no very major or major errors were seen, and minor errors were < or = 6%. Increased minor error rates were observed with disk diffusion (12%), Alamar (16%), Uniscept (16%), and conventional (overnight) MicroScan panels (16%). The errors were primarily with Enterococcus casseliflavus strains and organisms containing the vanB vancomycin resistance gene. Very major error rates of 10.3 and 20.7% were observed with Vitek and MicroScan Rapid (MS/Rapid) systems, respectively; however, only the MS/Rapid system produced major errors (13.3%). On repeat testing of discrepant isolates, the very major error rate with the Vitek system dropped to 3.4%, while the very major error rate with the MS/Rapid system increased to 27.6%; major errors with the MS/Rapid system were not resolved. Many of the commercial systems had only 4 dilutions of vancomycin, which resulted in up to 84% of values being off scale (e.g., Uniscept). Of the methods tested, most conventional broth- and agar-based methods proved to be highly accurate when incubation was done for a full 24 h, although several of the tests had high minor error rates. Automated systems continued to demonstrate problems in detecting low-level resistance.
Full Text
The Full Text of this article is available as a PDF (218.9 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Clark N. C., Cooksey R. C., Hill B. C., Swenson J. M., Tenover F. C. Characterization of glycopeptide-resistant enterococci from U.S. hospitals. Antimicrob Agents Chemother. 1993 Nov;37(11):2311–2317. doi: 10.1128/aac.37.11.2311. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Facklam R. R., Collins M. D. Identification of Enterococcus species isolated from human infections by a conventional test scheme. J Clin Microbiol. 1989 Apr;27(4):731–734. doi: 10.1128/jcm.27.4.731-734.1989. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Handwerger S., Raucher B., Altarac D., Monka J., Marchione S., Singh K. V., Murray B. E., Wolff J., Walters B. Nosocomial outbreak due to Enterococcus faecium highly resistant to vancomycin, penicillin, and gentamicin. Clin Infect Dis. 1993 Jun;16(6):750–755. doi: 10.1093/clind/16.6.750. [DOI] [PubMed] [Google Scholar]
- Huang M. B., Baker C. N., Banerjee S., Tenover F. C. Accuracy of the E test for determining antimicrobial susceptibilities of staphylococci, enterococci, Campylobacter jejuni, and gram-negative bacteria resistant to antimicrobial agents. J Clin Microbiol. 1992 Dec;30(12):3243–3248. doi: 10.1128/jcm.30.12.3243-3248.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Montecalvo M. A., Horowitz H., Gedris C., Carbonaro C., Tenover F. C., Issah A., Cook P., Wormser G. P. Outbreak of vancomycin-, ampicillin-, and aminoglycoside-resistant Enterococcus faecium bacteremia in an adult oncology unit. Antimicrob Agents Chemother. 1994 Jun;38(6):1363–1367. doi: 10.1128/aac.38.6.1363. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Navarro F., Courvalin P. Analysis of genes encoding D-alanine-D-alanine ligase-related enzymes in Enterococcus casseliflavus and Enterococcus flavescens. Antimicrob Agents Chemother. 1994 Aug;38(8):1788–1793. doi: 10.1128/aac.38.8.1788. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sahm D. F., Olsen L. In vitro detection of enterococcal vancomycin resistance. Antimicrob Agents Chemother. 1990 Sep;34(9):1846–1848. doi: 10.1128/aac.34.9.1846. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schaberg D. R., Culver D. H., Gaynes R. P. Major trends in the microbial etiology of nosocomial infection. Am J Med. 1991 Sep 16;91(3B):72S–75S. doi: 10.1016/0002-9343(91)90346-y. [DOI] [PubMed] [Google Scholar]
- Swenson J. M., Clark N. C., Ferraro M. J., Sahm D. F., Doern G., Pfaller M. A., Reller L. B., Weinstein M. P., Zabransky R. J., Tenover F. C. Development of a standardized screening method for detection of vancomycin-resistant enterococci. J Clin Microbiol. 1994 Jul;32(7):1700–1704. doi: 10.1128/jcm.32.7.1700-1704.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Tenover F. C., Tokars J., Swenson J., Paul S., Spitalny K., Jarvis W. Ability of clinical laboratories to detect antimicrobial agent-resistant enterococci. J Clin Microbiol. 1993 Jul;31(7):1695–1699. doi: 10.1128/jcm.31.7.1695-1699.1993. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Willey B. M., Kreiswirth B. N., Simor A. E., Willaims G., Scriver S. R., Phillips A., Low D. E. Detection of vancomycin resistance in Enterococcus species. J Clin Microbiol. 1992 Jul;30(7):1621–1624. doi: 10.1128/jcm.30.7.1621-1624.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]