Ability of clinical laboratories to detect antimicrobial agent-resistant enterococci

Abstract

To test the ability of clinical laboratories to detect antimicrobial resistance among enterococci, we sent four vancomycin-resistant enterococcal strains and one 13-lactamase-producing enterococcus to all 93 nongovernment, hospital-based clinical laboratories in New Jersey; 76 (82%) participated in the study. Each organism was tested by the laboratory's routine antimicrobial susceptibility testing method. The proportion of laboratories that correctly reported that an isolate was resistant to vancomycin varied according to the resistance level of the isolate: high-level resistance (MIC for Enterococcus faecium = 512 ,ug/ml), 96% of laboratories correct; moderate-level resistance (MIC for E. faecium = 64 ,ug/ml), 27% correct; low-level resistance (MIC for Enterococcusfaecalis = 32 p,g/ml), 16% correct; and intrinsic low-level resistance (MIC for Enterococcus gallinarum = 8 ,g/ml), 74% correct. The I-lactamase-producing E. faecalis isolate was identified as resistant to penicillin and ampicillin by 66 and 8% of laboratories, respectively, but only three laboratories recognized that it was a 1-lactamase producer. This survey suggests that many laboratories may fail to detect antimicrobial agent-resistant enterococci.

An interprovincial external quality assessment of the ability of Canadian laboratories to detect the vancomycin and penicillin resistance of Enterococcus faecium D366

“…Laboratories participating in our survey had no difficulty in detecting the low-level vancomycin resistance of E. faeciurn D366, regardless of the wide range of susceptibility testing methods used. In contrast, an earlier study showed that 71% of laboratories failed to detect vancomycin resistance in a strain of E. faecium with an MIC of 64 mg/L [20]. The improved current results probably reflect use of the 1992 NCCLS revised procedure.…”

“…Microscan users reported the greatest percentage of discordant susceptible results (88%) followed by Vitek (46%) and the breakpoint agar dilution (46%) methods. Lack of sensitivity of the Microscan panels and lack of specificity of the Vitek cards to detect ampicillin resistance have been noted previously [6,20]. The disk diffusion method was the most reliable at detecting the ampicillin resistance, although 19% of participating laboratories did report a falsely susceptible result.…”

Evaluation and characterization of multiresistant Enterococcus faecium from 12 U.S. medical centers

“…The disk diffusion results disagreed (false intermediate) with the results (resistant) of both other methods for only three isolates. Several studies have reported the inability of some susceptibility testing methods, especially automated systems and disk diffusion, to detect resistance to ,-lactams, aminoglycosides, and glycopeptides (9,16). On the other hand, our results indicate that the E test appears to be an acceptable alternative for testing enterococci against the antimicrobial VOL.…”

Vancomycin-resistant enterococci from nosocomial, community, and animal sources in the United States

“…E. faecium has been the most often isolated species and VanA has been the most often reported phenotype (7). Nonetheless, because of difficulties in detecting some VanB-type VRE (41,42) and because some studies have been designed to detect the high levels of resistance more characteristic of the VanA phenotype (24,25), VanB-type VRE could be more widespread than previously thought.…”