Clinical and epidemiological significance of enterococci intrinsically resistant to vancomycin (possessing the vanC genotype)

Abstract

Constitutive low-level vancomycin resistance is found intrinsically in certain enterococcal species and is encoded by vanC ligase genes. These intrinsically vancomycin-resistant enterococci (VRE) will be referred to as VANC VRE. A prospective study to determine the clinical and epidemiologic significance of VANC VRE was conducted. VANC VRE were recovered from the stools of 34 of 601 (5.7%) patients, a rate similar to that obtained for the stools of 100 outpatients in the community (5%). VANC VRE were also isolated from the nonstool specimens of 9 of 538 patients (1.7%), including two patients with bacteremia. No VRE of the vanA or vanB genotypes were detected in nonstool specimens. Eighty-two hospital contacts of the first 23 patients found to be colonized or infected with VANC VRE were screened, and 6 contacts were found to be gastrointestinal carriers of VANC VRE. However, typing of isolates from these 6 contacts by pulsed-field gel electrophoresis with SmaI showed the isolates to be unique and different from those recovered from the index patients. In fact, all VANC VRE isolates from different patients in this study were unique. A case-control study with patients who were negative when screened for VANC VRE as controls failed to identify any risk factor associated with colonization or infection with this organism. VANC VRE were infrequently recovered from clinical specimens but were occasionally found as part of the normal stool flora. Since no transmission between patients was documented, additional isolation procedures may not be necessary for patients colonized or infected with VANC VRE.

Determination of 16S rRNA Sequences of Enterococci and Application to Species Identification of Nonmotile Enterococcus gallinarum Isolates

“…This finding has im- portant implications for the clinical microbiology laboratory. E. gallinarum is pathogenic for humans (21,22); in a recent study, enterococci with vanC-associated vancomycin resistance were isolated from nonstool specimens of 9 of 538 patients (1.7%), including two patients with bacteremia who subsequently died (27). Furthermore, vancomycin treatment failure has been associated with intrinsic low-level vancomycin resistance both in humans and in animal models of experimental endocarditis (8,12,15).…”

“…There therefore exists a need to accurately and quickly differentiate enterococci with vanCassociated vancomycin resistance from vancomycin-susceptible enterococci. On the other hand, it has been suggested that vanC-associated vancomycin resistance is not a concern for infection control, because no nosocomial transmission of the involved organisms has been reported (27)(28)(29). Costly and cumbersome infection control precautions, such as those recommended for enterococci with vanA-and vanB-associated vancomycin resistance, may therefore not be necessary in the management of patients with vanC enterococci (9,11,13,16).…”

Use of Molecular and Reference Susceptibility Testing Methods in a Multicenter Evaluation of MicroScan Dried Overnight Gram-Positive MIC Panels for Detection of Vancomycin and High-Level Aminoglycoside Resistances in Enterococci

“…Recent reports have demonstrated the inability of many clinical laboratories (2,23,34) and commercial susceptibility testing systems (12,23,34) to detect glycopeptide resistance, especially patterns of low-or moderate-level resistance to vancomycin in enterococci (strains with a vanC genotype and certain strains of the vanB type). Enterococci with the vanC genotype, i.e., E. gallinarum and E. casseliflavus, which possess an intrinsic property of constitutive low-level VR (13,19), are infrequently recovered from clinical specimens (11,32). The clinical significance of resistance expressed by these organisms, as opposed to the significance of that expressed by vanA or vanB, or HLAR enterococci, remains unclear (32), and the implications of susceptible or intermediate vancomycin results for isolates of these species are also uncertain.…”

“…Enterococci with the vanC genotype, i.e., E. gallinarum and E. casseliflavus, which possess an intrinsic property of constitutive low-level VR (13,19), are infrequently recovered from clinical specimens (11,32). The clinical significance of resistance expressed by these organisms, as opposed to the significance of that expressed by vanA or vanB, or HLAR enterococci, remains unclear (32), and the implications of susceptible or intermediate vancomycin results for isolates of these species are also uncertain. A laboratory report of a VR isolate will initiate a cascade of infection control events that are both time-consuming and costly (5) and that should be focused on organisms of the vanA or vanB pattern.…”

“…PM-8 was also slightly superior to RBM in the detection of low-level vanB resistance; however, QA had the best ability to detect VR at a low level. The vanC resistances need further clarification as to clinical significance (13,19,32), since there remain testing problems because of their usual intermediate levels of vancomycin susceptibility (4 to 16 g/ml).…”