Revised approach for identification and detection of ampicillin and vancomycin resistance in Enterococcus species by using MicroScan panels

Comparison of Enterococcus faecium and Enterococcus faecalis Strains isolated from water and clinical samples: antimicrobial susceptibility and genetic relationships

Enterococci are part of the normal intestinal flora in a large number of mammals, and these microbes are currently used as indicators of fecal contamination in water and food for human consumption. These organisms are considered one of the primary causes of nosocomial and environmental infections due to their ability to survive in the environment and to their intrinsic resistance to antimicrobials. The aims of this study were to determine the biochemical patterns and antimicrobial susceptibilities of Enterococcus faecalis and E. faecium isolates from clinical samples and from water (groundwater, water from the Xochimilco wetland, and treated water from the Mexico City Metropolitan Area) and to determine the genetic relationships among these isolates. A total of 121 enterococcus strains were studied; 31 and 90 strains were isolated from clinical samples and water (groundwater, water from the Xochimilco wetland, and water for agricultural irrigation), respectively. Identification to the species level was performed using a multiplex PCR assay, and antimicrobial profiles were obtained using a commercial kit. Twenty-eight strains were analyzed by pulsed-field gel electrophoresis (PFGE). E. faecium strains isolated from water showed an atypical biochemical pattern. The clinical isolates showed higher resistance to antibiotics than those from water. Both the enterococci isolated from humans, and those isolated from water showed high genetic diversity according to the PFGE analysis, although some strains seemed to be closely related. In conclusion, enterococci isolated from humans and water are genetically different. However, water represents a potential route of transmission to the community and a source of antimicrobial resistance genes that may be readily transmitted to other, different bacterial species.

Expert systems in clinical microbiology

This review aims to discuss expert systems in general and how they may be used in medicine as a whole and clinical microbiology in particular (with the aid of interpretive reading). It considers rule-based systems, pattern-based systems, and data mining and introduces neural nets. A variety of noncommercial systems is described, and the central role played by the EUCAST is stressed. The need for expert rules in the environment of reset EUCAST breakpoints is also questioned. Commercial automated systems with on-board expert systems are considered, with emphasis being placed on the "big three": Vitek 2, BD Phoenix, and MicroScan. By necessity and in places, the review becomes a general review of automated system performances for the detection of specific resistance mechanisms rather than focusing solely on expert systems. Published performance evaluations of each system are drawn together and commented on critically.

Prevalence of vancomycin-resistant Enterococcus fecal colonization among kidney transplant patients

Background

End stage renal disease patients are at risk of Vancomycin-Resistant Enterococcus (VRE) infections. The first reports of VRE isolation were from hemodialysis patients. However, to date, VRE fecal colonization rates as well as associated risk factors in kidney transplant patients have not yet been established in prospective studies.

Methods

We collected one or two stool samples from 280 kidney transplant patients and analysed the prevalence of VRE and its associated risk factors. Patients were evaluated according to the post-transplant period: group 1, less than 30 days after transplantation (102 patients), group 2, one to 6 months after transplantation (73 patients) and group 3, more than 6 months after transplantation (105 patients).

Results

The overall prevalence rate of fecal VRE colonization was 13.6% (38/280), respectively 13.7% for Group 1, 15.1% for group 2 and 12.4% for group 3. E. faecium and E. faecalis comprised 50% of all VRE isolates. No immunologic variables were clearly correlated with VRE colonization and no infections related to VRE colonization were reported.

Conclusion

Fecal VRE colonization rates in kidney transplant patients were as high as those reported for other high-risk groups, such as critical care and hemodialysis patients. This high rate of VRE colonization observed in kidney transplant recipients may have clinical relevance in infectious complications.

Clinical features and outcomes of bacteremia caused by Enterococcus casseliflavus and Enterococcus gallinarum: analysis of 56 cases

The clinical significance and virulence potential of Enterococcus casseliflavus/flavescens and Enterococcus gallinarum are still uncertain. We retrospectively analyzed 56 cases of significant bacteremia caused by E. casseliflavus or E. gallinarum. Of these cases, 25 (44.6%) were associated with polymicrobial bacteremia, and 43 (76.8%) were associated with entry via the biliary tract. Resistance to vancomycin was observed in 17 (30.4%) of these 56 patients, and this resistance was significantly associated with E. gallinarum bacteremia (adjusted odds ratio [AOR], 10.56; 95% confidence interval [CI], 2.41-46.27) and bacteremia without biliary tract origin (AOR, 6.74; 95% CI, 1.44-31.67). The crude mortality rate was 13%, and the bacteremia-related mortality rate was 1.9%. In conclusion, bacteremia due to E. casseliflavus and E. gallinarum is commonly associated with biliary tract disease and may be associated with a low risk of mortality.

Resistance to beta-lactams and glycopeptides in staphylococci and streptococci

Molecular mechanisms of the action of beta-lactam and glycopeptide antibiotics, as well as genetic background and phenotypical features of the resistance of staphylococci, streptococci and enterococci to these antibiotics are reviewed. Furthermore, susceptibility patterns concerning beta-lactam and glycopeptide drugs of staphylococcal, streptococcal, as well as enterococcal strains isolated from clinical specimens at the Semmelweis University of Medicine, Budapest, Hungary between January 1997 and December 2000 are also presented.

Evaluation of 15 motility media and a direct microscopic method for detection of motility in enterococci

Isolation of motile, vanC enterococci has yet to be a major infection control concern; however, rapid detection still is important. We evaluated 15 motility media from three manufacturers and a 2-h direct microscopic method for accurate detection of 89 enterococcal strains, including 72 vanC enterococcal strains. Resistance genes were confirmed by a multiplex PCR method with the vanC gene detected in all motile enterococci. Motility in the 72 vanC enterococci was detected at 30 degrees C within 72 h in BD Biosciences motility nitrate medium and in Remel motility B medium, motility B medium supplemented with methyl-alpha-D-glucopyranoside (investigational), motility S medium, motility test medium, and motility test medium with tetrazolium indicator. Motility was also observed for all vanC enterococci with the 2-h direct (30 degrees C incubation) microscopic detection method. All Enterococcus faecalis and Enterococcus faecium isolates were observed to be nonmotile in all media and by the direct microscopic method. Since differences between the various motility media tested were observed, the medium used for detection of enterococcal motility must be selected carefully.

Enterococcus gallinarum endocarditis occurring on native heart valves

We report the first case of Enterococcus gallinarum endocarditis developing on normal native heart valves. Using phenotypic and molecular methods, a precise identification of this naturally vancomycin-resistant species allowed an optimal antibiotic therapy and the patient's recovery.

Evaluation of an automated system for the identification and antimicrobial susceptibility testing of enterococci

The performance of a new version of an automated system panel, the Positive Combo Panel Type 11 of MicroScan WalkAway 96 (WA96; Dade Behring) was evaluated and compared to that of reference methods for the identification and for antimicrobial susceptibility testing of the different enterococcal species. A total of 376 enterococcal isolates were tested. The MicroScan WA96 correctly identified 99.6% (266/267), 78.3% (18/23) and 68.6% (59/86) of Enterococcus faecalis, Enterococcus faecium and species other than E. faecalis and E. faecium, respectively. Although low probability of accurate identification was obtained for 37 (9.8%) strains, the system indicated that supplementary tests were necessary for precise identification of 8 (9.3%) among the 86 strains included in the non-faecalis/non-faecium group and of 3 (13.0%) among the E. faecium isolates. In comparison to the agar screening method, the percentage of agreement for detection of resistance markers by the automated system was 90.2% (37/41) for ampicillin, 90.6% (48/53) for high-level resistance to streptomycin (HLRS), 96.4% (80/83) for high-level resistance to gentamicin (HLRG), and 100% (14/14) for vancomycin. The results indicate that the MicroScan WA96 performed well for the identification of E. faecalis and typical E. faecium isolates, and for the detection of resistance to vancomycin and HLRG. However, the system still needs further improvement in order to provide reliable results for the characterization of the other enterococcal species, including atypical variants of E. faecium.

Clinical and epidemiological features of Enterococcus casseliflavus/flavescens and Enterococcus gallinarum bacteremia: a report of 20 cases

The clinical significance of intrinsically vancomycin-resistant enterococci is not yet fully established, as these organisms are infrequently recovered from clinical specimens. We report our experience with 20 cases of Enterococcus gallinarum and Enterococcus casseliflavus/flavescens bacteremia in humans from 1992 through 1998. Sixteen cases of bacteremia were caused by E. gallinarum. Underlying conditions were present in 19 (95%) of the patients and included malignancy, receipt of transplant, and Caroli's disease. Polymicrobial bacteremia was present in 9 patients (45%). E. gallinarum and E. casseliflavus/flavescens, although they are infrequently isolated from clinical specimens, may cause serious invasive infections.

Outbreak of vancomycin-resistant Enterococcus faecium in a neonatal intensive care unit

An outbreak of vancomycin-resistant Enterococcus faecium involving 28 infants in a neonatal intensive care unit was observed. Successful control of the outbreak was achieved following use of patient and staff cohorting, contact isolation precautions, patient and environmental surveillance cultures, environmental decontamination, molecular typing, introduction of an alcohol-based hand disinfectant, and decreased use of vancomycin.

Classification and identification of enterococci: a comparative phenotypic, genotypic, and vibrational spectroscopic study

Rapid and accurate identification of enterococci at the species level is an essential task in clinical microbiology since these organisms have emerged as one of the leading causes of nosocomial infections worldwide. Vibrational spectroscopic techniques (infrared [IR] and Raman) could provide potential alternatives to conventional typing methods, because they are fast, easy to perform, and economical. We present a comparative study using phenotypic, genotypic, and vibrational spectroscopic techniques for typing a collection of 18 Enterococcus strains comprising six different species. Classification of the bacteria by Fourier transform (FT)-IR spectroscopy in combination with hierarchical cluster analysis revealed discrepancies for certain strains when compared with results obtained from automated phenotypic systems, such as API and MicroScan. Further diagnostic evaluation using genotypic methods-i.e., PCR of the species-specific ligase and glycopeptide resistance genes, which is limited to the identification of only four Enterococcus species and 16S RNA sequencing, the "gold standard" for identification of enterococci-confirmed the results obtained by the FT-IR classification. These results were later reproduced by three different laboratories, using confocal Raman microspectroscopy, FT-IR attenuated total reflectance spectroscopy, and FT-IR microspectroscopy, demonstrating the discriminative capacity and the reproducibility of the technique. It is concluded that vibrational spectroscopic techniques have great potential as routine methods in clinical microbiology.

Identification of Enterococcus species and phenotypically similar Lactococcus and Vagococcus species by reverse checkerboard hybridization to chaperonin 60 gene sequences

Data from four recent studies (S. H. Goh et al., J. Clin. Microbiol. 36:2164-2166, 1998; S. H. Goh et al., J. Clin. Microbiol. 34:818-823, 1996; S. H. Goh et al., J. Clin. Microbiol. 35:3116-3121, 1997; A. Y. C. Kwok et al., Int. J. Syst. Bacteriol. 49:1181-1192, 1999) suggest that an approximately 600-bp region of the chaperonin 60 (Cpn60) gene, amplified by PCR with a single pair of degenerate primers, has utility as a potentially universal target for bacterial identification (ID). This Cpn60 gene ID method correctly identified isolates representative of numerous staphylococcal species and Streptococcus iniae, a human and animal pathogen. We report herein that this method enabled us to distinguish clearly between 17 Enterococcus species (Enterococcus asini, Enterococcus rattus, Enterococcus dispar, Enterococcus gallinarum, Enterococcus hirae, Enterococcus durans, Enterococcus cecorum, Enterococcus faecalis, Enterococcus mundtii, Enterococcus casseliflavus, Enterococcus faecium, Enterococcus malodoratus, Enterococcus raffinosus, Enterococcus avium, Enterococcus pseudoavium, Enterococcus new sp. strain Facklam, and Enterococcus saccharolyticus), and Vagococcus fluvialis, Lactococcus lactis, and Lactococcus garvieae. From 123 blind-tested samples, only two discrepancies were observed between the Facklam and Collins phenotyping method (R. R. Facklam and M. D. Collins, J. Clin. Microbiol. 27:731-734, 1989) and the Cpn60 ID method. In each case, the discrepancies were resolved in favor of the Cpn60 ID method. The species distributions of the 123 blind-tested isolates were Enterococcus new sp. strain Facklam (ATCC 700913), 3; E. asini, 1; E. rattus, 4; E. dispar, 2; E. gallinarum, 20; E. hirae, 9; E. durans, 9; E. faecalis, 12; E. mundtii, 3; E. casseliflavus, 8; E. faecium, 25; E. malodoratus, 3; E. raffinosus, 8; E. avium, 4; E. pseudoavium, 1; an unknown Enterococcus clinical isolate, sp. strain R871; Vagococcus fluvialis, 4; Lactococcus garvieae, 3; Lactococcus lactis, 3; Leuconostoc sp., 1; and Pediococcus sp., 1. The Cpn60 gene ID method, coupled with reverse checkerboard hybridization, is an effective method for the identification of Enterococcus and related organisms.

Sequencing the gene encoding manganese-dependent superoxide dismutase for rapid species identification of enterococci

Simple PCR and sequencing assays that utilize a single pair of degenerate primers were used to characterize a 438-bp-long DNA fragment internal (sodA(int)) to the sodA gene encoding the manganese-dependent superoxide dismutase in 19 enterococcal type strains (Enterococcus avium, Enterococcus casseliflavus, Enterococcus cecorum, Enterococcus columbae, Enterococcus dispar, Enterococcus durans, Enterococcus faecalis, Enterococcus faecium, Enterococcus flavescens, Enterococcus gallinarum, Enterococcus hirae, Enterococcus malodoratus, Enterococcus mundtii, Enterococcus pseudoavium, Enterococcus raffinosus, Enterococcus saccharolyticus, Enterococcus seriolicida, Enterococcus solitarius, and Enterococcus sulfureus). Sequence analysis of the sodA(int) fragments enabled reliable identification of 18 enterococcal species, including E. casseliflavus-E. flavescens and E. gallinarum. The sodA(int) fragments of E. casseliflavus and E. flavescens were almost identical (99.5% sequence identity), which suggests that they should be associated in a single species. Our results confirm that the sodA gene constitutes a more discriminative target sequence than 16S rRNA gene in differentiating closely related bacterial species.

Evaluation of the revised MicroScan dried overnight gram-positive identification panel to identify Enterococcus species

The revised MicroScan Dried Overnight Gram-Positive Identification panel was evaluated for its efficacy at identifying Enterococcus species in comparison with conventional biochemical tests. Supplemental testing of ampicillin-susceptible Enterococcus faecium for motility and the ability to acidify methyl-alpha-D-glucopyranoside helped recognize E. gallinarum and increased the accuracy of the panel for identifying Enterococcus species to 98.5%.

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

OBJECTIVE: To evaluate the ability of Canadian laboratories to identify enterococci and detect low-level resistance to penicillin, ampicillin and vancomycin in five provinces and two territories by two external quality assessment schemes. METHODS: Enterococcus faecium, strain D366, with minimum inhibitory concentrations for vancomycin and penicillin of 32 and 16 mg/L respectively, was distributed during a routine proficiency survey. Laboratories were required to culture and identify the isolate and to test antimicrobial susceptibility. Participants were assessed against consensus reference values. RESULTS: Three hundred and sixty-four hospital, commercial and public-health laboratories participated, using their established procedures for patient samples. The isolate was identified to the species level by 222 (61%) laboratories and to the genus level by a further 98 participants. Forty-four failed to meet the expected standard. Vancomycin resistance was detected by 94%. Those reporting a falsely susceptible result used disk diffusion testing. Penicillin resistance was noted by 250 of 258 laboratories reporting on this agent. An incorrect ampicillin-susceptible finding was reported by 62 of 147 laboratories using automated microdilution or agar dilution methods. CONCLUSIONS: Most laboratories identified the isolate to an appropriate level. Detection of low-level vancomycin and penicillin resistance was achieved by the majority. Ampicillin resistance was less readily detected.

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

Three different methodologies, reduction of litmus milk (LM) and acidification of arabinose (ARA), acidification of methyl-alpha-D-glucopyranoside (MGP), and rapid motility (RM), for differentiating isolates of Enterococcus casseliflavus and Enterococcus gallinarum (intrinsically vancomycin-resistant enterococci [IVRE]) from Enterococcus faecalis and Enterococcus faecium were evaluated. All 33 isolates of E. faecalis tested reduced LM within 4 h and were negative in all other tests, while the 53 isolates of E. faecium were ARA positive only. In contrast, 45 of 46 (98%) IVRE isolates examined (26 E. casseliflavus and 20 E. gallinarum isolates) acidified MGP, 41 of 46 (89%) were LM and ARA positive, and 45 of 46 (98%) were RM positive. Acidification of MGP was therefore the single most useful test for differentiating IVRE from vancomycin-resistant E. faecium and E. faecalis; however, a combination of LM-ARA and RM testing enabled the correct designation of organisms without the need for overnight incubation.

Proficiency of clinical laboratories in and near Monterrey, Mexico, to detect vancomycin-resistant enterococci

Early detection of vancomycin-resistant enterococci is important for preventing its spread among hospitalized patients. We surveyed the ability of eight hospital laboratories in and near Monterrey, Mexico, to detect vancomycin resistance in Enterococcus spp. and found that although laboratories can reliably detect high-level vancomycin resistance, many have difficulty detecting low-level resistance.

Colonization and microbiology of the motile enterococci in a patient population

The motile enterococci with the vanC gene have intrinsic low-level resistance to vancomycin, but have not been implicated in a nosocomial outbreak. We determined the colonization rate of motile enterococci in hospitalized and nonhospitalized patients. Perianal or stool specimens were cultured in Enterococcosel broth supplemented with 6 micrograms of vancomycin per mL. Rapid motility and pigment tests were performed on all enterococci isolated. A total of 82 motile and/or pigmented enterococci were isolated from 679 patients for a colonization rate of 12.1%. There were 43 Enterococcus gallinarum, 32 Enterococcus casseliflavus, 4 Enterococcus flavescens, and 3 Enterococcus mundtii identified. The E. gallinarum vancomycin MIC90 was 32 micrograms/mL and the E. casseliflavus vancomycin MIC90 was 8 micrograms/mL.

Use of tests for acidification of methyl-alpha-D-glucopyranoside and susceptibility to efrotomycin for differentiation of strains of Enterococcus and some related genera

A total of 107 Enterococcus strains, 10 Vagococcus fluvialis strains, and 8 Lactococcus garvieae strains were tested for acidification of methyl-alpha-D-glucopyranoside (MGP) and susceptibility to 100-microg efrotomycin (EFRO) disks. All 26 strains of Enterococcus casseliflavus, including 3 nonmotile and 2 nonpigmented strains, acidified MGP and were resistant to EFRO. All 22 strains of Enterococcus gallinarum, including 5 nonmotile strains, also acidified MGP and were resistant to EFRO. None of the 26 strains of Enterococcus faecium acidified MGP, and all were susceptible to EFRO. Although all 12 Enterococcus faecalis strains were also negative in the MGP test, they were resistant to EFRO. Other enterococcal strains gave variable results. All 10 strains of V. fluvialis and all 8 strains of L. garvieae gave positive and negative results, respectively, in the MGP test and were, respectively, resistant and susceptible to EFRO. These results indicate that tests of the production of acid from MGP and susceptibility to EFRO can be used as adjunct tests in the identification of typical and atypical strains of enterococci in the clinical microbiology laboratory.

Are clinical laboratories in California accurately reporting vancomycin-resistant enterococci?

In order to determine whether hospital-based clinical laboratories conducting active surveillance for vancomycin-resistant enterococci in three San Francisco Bay area counties (San Francisco, Alameda, and Contra Costa counties) were accurately reporting vancomycin resistance, five vancomycin-resistant enterococcal strains and one vancomycin-susceptible beta-lactamase-producing enterococcus were sent to 31 of 32 (97%) laboratories conducting surveillance. Each strain was tested by the laboratory's routine antimicrobial susceptibility testing method. An Enterococcus faecium strain with high-level resistance to vancomycin (MIC, 512 microg/ml) was correctly reported as resistant by 100% of laboratories; an E. faecium strain with moderate-level resistance (MIC, 64 microg/ml) was correctly reported as resistant by 91% of laboratories; two Enterococcus faecalis strains with low-level resistance (MICs, 32 microg/ml) were correctly reported as resistant by 97 and 56% of laboratories, respectively. An Enterococcus gallinarum strain with intrinsic low-level resistance (MIC, 8 microg/ml) was correctly reported as intermediate by 50% of laboratories. A beta-lactamase-producing E. faecalis isolate was correctly identified as susceptible to vancomycin by 100% of laboratories and as resistant to penicillin and ampicillin by 68 and 44% of laboratories, respectively; all 23 (74%) laboratories that tested for beta-lactamase recognized that it was a beta-lactamase producer. This survey indicated that for clinically significant enterococcal isolates, laboratories in the San Francisco Bay area have problems in detecting low- to moderate-level but not high-level vancomycin resistance. Increasing accuracy of detection and prompt reporting of these isolates and investigation of cases are the next steps in the battle for control of the spread of vancomycin resistance.

Vancomycin-resistant enterococcus. Detection, epidemiology, and control measures

VRE have spread rapidly since their initial description in 1988. Although much has been learned about the epidemiology of VRE, further studies are needed to establish the reservoirs of the organism and the relative importance of various modes of transmission. There is considerable anecdotal evidence that nosocomial transmission of VRE can be thwarted by using measures such as those recommended by HICPAC, especially if they are implemented promptly after VRE have been introduced into hospitals.