Enterococcus faecalis resistant to vancomycin and teicoplanin (VanA phenotype) isolated from a bone marrow transplanted patient in Brazil

Abstract

We report for the first time in Brazil, a patient from whom an Enterococcus faecalis VanA phenotype was isolated. Glycopeptide resistance is not commonly observed in Enterococcus faecalis, so this finding is of great concern since this species is responsible for 90% of enterococcal infections in Brazil. The isolate was recovered from a surveillance rectal swab culture from a patient with acute lymphocytic leukemia (ALL). Identification to the species level was performed by conventional biochemical tests and Vitek GPI cards. Antimicrobial susceptibility testing was evaluated by use of broth microdilution and Etest (AB BIODISK, Solna, Sweden) methods. The isolate was identified as E. faecalis and was considered resistant to both vancomycin (MIC, > 256 mug/mL) and teicoplanin (MIC, 256 mug/mL). The isolate also showed high level resistance to gentamicin and streptomycin (MICs, > 1024 mug/mL), but was considered susceptible to ampicillin (MIC, 4 mug/mL). Although the frequency of enterococcal infections is very low in most Latin America countries, the finding of glycopeptide (VanA) resistance in E. faecalis increases concern about apreading antimicrobial resistance in this region.

Enterococcus faecalis; glycopeptide resistance; vanA; initial case report; transplant

Enterococcus faecalis Resistant to Vancomycin and Teicoplanin (VanA Phenotype) Isolated from a Bone Marrow Transplanted Patient in Brazil

Rosangela F. Cereda, Helio S. Sader,Ronald N. Jones, Lilian Sejas, Antônia M. Machado, Yara P. Zanatta, Sinaida T. M. S. Rego and Eduardo A. S. Medeiros

Special Clinical Microbiology Laboratory (LEMC) and Nosocomial Infection Control Committee, Infectious Disease Division, Federal University of São Paulo, São Paulo, Brazil; Medical Microbiology Division, Department of Pathology, University of Iowa College of Medicine, Iowa City, Iowa; Central Laboratory, São Paulo Hospital, São Paulo, Brazil

We report for the first time in Brazil, a patient from whom an Enterococcus faecalis VanA phenotype was isolated. Glycopeptide resistance is not commonly observed in Enterococcus faecalis, so this finding is of great concern since this species is responsible for 90% of enterococcal infections in Brazil. The isolate was recovered from a surveillance rectal swab culture from a patient with acute lymphocytic leukemia (ALL). Identification to the species level was performed by conventional biochemical tests and Vitek GPI cards. Antimicrobial susceptibility testing was evaluated by use of broth microdilution and Etest (AB BIODISK, Solna, Sweden) methods. The isolate was identified as E. faecalis and was considered resistant to both vancomycin (MIC, > 256 mg/mL) and teicoplanin (MIC, 256 mg/mL). The isolate also showed high level resistance to gentamicin and streptomycin (MICs, > 1024 mg/mL), but was considered susceptible to ampicillin (MIC, 4 mg/mL). Although the frequency of enterococcal infections is very low in most Latin America countries, the finding of glycopeptide (VanA) resistance in E. faecalis increases concern about apreading antimicrobial resistance in this region.

Key words: Enterococcus faecalis, glycopeptide resistance, vanA, initial case report, transplant.

Glycopeptide-resistant enterococci, best known as vancomycin-resistant enterococci (VRE), have emerged as an important human pathogen responsible for serious systemic infections, especially in debilitated hosts with lowered defense mechanisms [1]. The problem is complicated by the inherent drug resistance of this pathogen. Enterococcus faecalis, the most commonly occurring species in this genus, has acquired high-level aminoglycoside resistance, and glycopeptide resistance, although ampicillin resistance is still rarely found.

E. faecium, the second most frequent enterococcal species, is inherently more resistant to many antimicrobial agents. In Brazil, approximately one half of clinical E. faecium isolates are resistant to ampicillin. In addition, high-level aminoglycoside resistance and glycopeptide resistance are usually much higher among this species when compared to E. faecalis [2].

Three different genotypes have been described in E. faecium and E. faecalis: vanA, vanB, and vanD. These genes encode either high-, intermediate-, or low-level resistance to glycopeptides. In addition of these genotypes, VRE is categorized in two general phenotypes: 1) VanA or Class A – high level resistance to vancomycin and teicoplanin; and 2) VanB or Class B – the isolates are resistant to vancomycin but remain susceptible to teicoplanin (MIC, £ 8 mg/mL). Although E. faecalis is by far the most frequently isolated enterococcal species, VanA phenotype is rarely found in this species. A fourth genotype, vanC, is intrinsic for E. gallinarum and E. casseliflavus, and encodes resistance to vancomycin (low-level) but not to teicoplanin [3, 4].

The main source or reservoir of VRE remains unclear, but the acquisition of the strain may follow previous colonization of the patient (endogenous acquisition) or it may be acquired from other patients (exogenous acquisition) [3, 4]. The acquisition of VRE via the food chain has been proposed in some studies, since vanA E. faecium has been isolated from farm animals and from animal-derived food products [5, 6]. The gastrointestinal tract is considered an important reservoir from which dissemination of resistant strains of enterococci may occur [7]. Nosocomial outbreaks have been associated with gastrointestinal colonization by VRE in patients with prolonged hospitalization and prolonged use of broad-spectrum antimicrobial agents [8].

Once VRE becomes established in a clinical unit or medial center, it may cause a range of infections associated with high mortality. Moreover, there is a potential for glycopeptide resistance genes to spread to other, more virulent organisms [3]. Since there is no widely accepted therapy for infections due to multiresistant VRE, it is essential to limit the spread of these microorganisms.

Although a few cases of infections due to vancomycin-resistant E. faecium have recently been described in Brazil [9], this is the first case involving an E. faecalis strain.

Case Report

A 23-year-old woman with acute lymphocytic leukemia (ALL) was hospitalized at the São Paulo Hospital (Federal University of São Paulo, São Paulo, Brazil) in December, 1997. She had several previous hospitalizations and antimicrobial treatment with glycopeptides, cephalosporins, carbapenem, and fluoroquinolones. On January 9, 1998, after receiving acyclovir, gancyclovir, fluconazole, cotrimoxazole, enduxan, and methotrexate for 7 days, she received a bone marrow transplant. A Hickman catheter was placed for drug administration. In addition, the patient had a catheter placed for bladder irrigation for 3 days. No other device was used during hospitalization. On January 12, the patient had an elevated temperature and mucositis. Because of the fever, ceftazidime and amikacin were initiated. After 24 hours, the amikacin was replaced with vancomycin and meropenem. Four days later, the patient was still febrile and the mucositis was grade III in intensity. Amphotericin B was introduced at this time. After 5 days, the patient became afebrile and asymptomatic. On January 30, the patient's white cell count was 900/mm³ and all antimicrobial agents were withdrawn. Four days later she was discharged.

A surveillance rectal swab culture collected on January 14, grew E. faecalis. The swab was plated on a blood agar screen plate containing vancomycin 6 mg/mL, aztreonam 60 mg/mL, and nystatin 12.5 mg/mL. After incubation at 37 °C for 24 hours, Gram's stain was performed and Gram-positive cocci were detected and subcultured on non-selective sheep blood agar. Identification to the species level was performed by conventional methods proposed by Fackland and Collins [10]. Vancomycin, teicoplanin, ampicillin, gentamicin, and streptomycin sensitivity were evaluated by the Etest (AB BIODISK, Solna, Sweden) method [11]. The MIC results were as follows: vancomycin > 256 mg/mL (resistant), teicoplanin 256 mg/mL (resistant), ampicillin 4 mg/mL (susceptible), gentamicin and streptomycin > 1,024 mg/mL (high-level resistance). The results for other antimicrobial agents are shown as in Table 1. A double zone of inhibition was observed for vancomycin and teicoplanin. The strain was sent to the University of Iowa (Iowa City, IA, USA) for further characterization. Local results were confirmed and the same double zone phenomenon was observed. In addition, the strain demonstrated a double zone for ampicillin (Table 2). Colonies in the Etest double zones (DZ) of ampicillin, teicoplanin, and vancomycin were collected and tested separately. Two of 3 DZ isolates demonstrated identical susceptibility testing results by Etest, but the isolate subcultured from the DZ on the ampicillin strip (isolate number 3) was susceptible to both vancomycin and teicoplanin (Table 2). The pulsed-field gel electrophoresis (PFGE – Figure 1)[12] and ribotype (Riboprinter, E. I. duPont the Nemours, Wilmington, DE, USA) [13] were identical for all 3 isolates and the original strain, and the vanA gene was identified in the original strain and both DZ isolates with the VanA phenotype (vancomycin DZ isolate and teicoplanin DZ isolate). Additional PCR tests [14] confirmed high-level gentamicin resistance and the species identifications, e.g. E. faecalis (Table 2). A plasmid analysis was performed and the vanA samples presented an identical profile (Figure 2) [15]. In spite of repeating the test several times and using different enzymes, we were not able to evaluate the plasmid analysis on isolate number 3 (ampicillin DZ isolate).

Discussion

Enterococcal infections can be associated with significant morbidity and mortality because they often occur in critically ill patients, especially those receiving organ transplants [1, 3]. If the strain reported here had caused a systemic infection, the treatment would have been very difficult. Isolates with high-level resistance to aminoglycosides are refractory to the synergistic effects that occur when these compounds are associated with cell-wall active drugs, such as b-lactams and glycopeptides. Multiple risk factors are related to infection by VRE, and colonization (like the case reported here) usually precedes the infection [16]. VRE carriage tends to be prolonged (from 19 to 303 days), and a patient whose gastrointestinal tract is colonized with VRE may function as a reservoir and facilitate the nosocomial dissemination of this pathogen. In addition, these patients will have a sustained risk for developing VRE infection [7, 17].

Over the last 3 years, our prospective VRE surveillance program has not identified any glycopeptide resistant strain [18]. Rectal swabs are obtained twice weekly from all ICU patients. The swab is plated on a selective agar screen plate. A total of 516 rectal swabs were cultured during a 17-month period and 37 vancomycin-intermediate enterococci isolates (MIC, 16 mg/mL) were recovered from 11 patients (1.2%). These isolates were identified as E. gallinarum (28 isolates), E. casseliflavus (5 isolates), E. faecalis (3 isolates), and E. faecium (1 isolate). vanA, vanB or vanC genes were not identified among E. faecalis or E. faecium strains. Although our medical center has several important risk factors for the appearance of VRE (600-bed university hospital, vancomycin use of 245 defined daily dose/1000 bed-days in the intensive care unit), this is the first glycopeptide-resistant E. faecalis strain identified.

Despite the fact that one isolate had a distinct vancomycin susceptibility pattern by Etest, the PFGE and ribotyping results of all isolates analyzed were identical. The hypothesis of mixed culture was excluded because all isolates had identical PFGE and ribotyping patterns (Figure 1). However, as previously observed by Woodford, et al. [19], PFGE analysis and the resistance phenotype may not be sufficient to accurately define the epidemiology of enterococci. These results reinforce the difficulties found in the characterization of VRE isolates. The fact that one of these isolates separated from the Etest double zones (the ampicillin DZ isolate) had a vancomycin MIC distinct from the other isolates with identical chromosomal patterns, may be explained by the loss of the plasmid containing vanA gene, since we could not detect plasmid in this vancomycin-susceptible isolate.

The detection of the present case, as well as other cases of colonization/infection due to VRE in Brazil, warns us of for the very recent appearance and dissemination of this important cause of nosocomial infections in our environment. A surveillance program is necessary to rapidly detect and control the appearance and dissemination of VRE on a nation-wide basis. The microbiology laboratories have an important role as the first line of defense by detecting these resistant strains accurately and quickly. Measures for preventing the spread of VRE in hospitals include the application of strict isolation precautions and the implementation of effective antimicrobial use control programs.

In summary, the clinical laboratories in Brazil must be prepared to detect VRE, and infection control personnel should be prepared to contain potential outbreaks before the pathogen becomes endemic.

Acknowledgements

We are very grateful to Ana C. Gales, Richard Hollis, Stacy Coffman and Steve Marshall (Medical Microbiology Division, Department of Pathology, University of Iowa College of Medicine, Iowa City, Iowa), who assisted with the characterization of this strain.

Received on 23 June 2000; revised 4 October 2000.

Address for correspondence: Helio S. Sader, M.D. Laboratório Especial de Microbiologia Clínica - Infectious Disease Division - Federal University of São Paulo. Rua Botucatu, 740. São Paulo, SP – Zip Code: 04023-063 – Brazil. Phone: + (55 11) 5571-5180 / 5576-4393 / 5081-2819. Fax: + (55 11) 543-3013 / 571-5180. E-mail: [e-mail]

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Publication Dates

• Publication in this collection
  29 Oct 2001
• Date of issue
  Feb 2001

History

• Received
  23 June 2000
• Reviewed
  04 Oct 2000