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Vancomycin variable Enterococcus (VVE), E. faecium, harbouring the vanA gene complex

2020; Elsevier BV; Volume: 53; Issue: 5 Linguagem: Inglês

10.1016/j.pathol.2020.08.030

1465-3931

John Merlino, Timothy Gray,

Bacterial Identification and Susceptibility Testing

In this article we describe the isolation from a blood culture specimen of a vancomycin variable Enterococcus (VVE), Enterococcus faecium, harbouring the vanA gene complex and a methicillin resistant Staphylococcus aureus (MRSA). We highlight the importance of using molecular methods for detecting VVE from sterile sites. VVE are E. faecium harbouring the vanA gene or vanB gene complex but being phenotypically vancomycin susceptible. VVE vanA was first described in 2011.1Gagnon S. Levesque S. Lefebvre B. et al.vanA-containing Enterococcus faecium susceptible to vancomycin and teicoplanin because of major nucleotide deletions in Tn1546.J Antimicrob Chemother. 2011; 66: 2758-2762Crossref PubMed Scopus (32) Google Scholar VVE can only be detected by molecular methods and cannot be cultured on selective vancomycin containing media. Different clones of VVE have caused nosocomial outbreaks.2Hammerum A.M. Justesen U.S. Pinholt M. et al.Surveillance of vancomycin-resistant enterococci reveals shift in dominating clones and national spread of a vancomycin-variable vanA Enterococcus faecium ST1421-CT1134 clone, Denmark, 2015 to March 2019.Euro Surveill. 2019; 24: 1-5Crossref Scopus (17) Google Scholar This makes the detection of VVE important in clinical samples in order to ensure relevant antibiotic treatment and in screening samples to mitigate nosocomial spread. VVE detection is challenging; the clone is likely to be unrecognised, which facilitates further spread. VVE outbreaks through transmission in health care settings have been described in previous studies. Hammerum et al. describe a clonal shift in vanA E. faecium isolates from clinical samples obtained from patients in Denmark from 2015 to the first quarter (Q1) of 2019. They report in 2019 that VVE ST1421-CT1134 vanA E. faecium became the most dominant vanA E. faecium clone and has spread throughout Denmark.2Hammerum A.M. Justesen U.S. Pinholt M. et al.Surveillance of vancomycin-resistant enterococci reveals shift in dominating clones and national spread of a vancomycin-variable vanA Enterococcus faecium ST1421-CT1134 clone, Denmark, 2015 to March 2019.Euro Surveill. 2019; 24: 1-5Crossref Scopus (17) Google Scholar In Australia in 2018 the Australian Group of Antimicrobial Resistance (AGAR) reported 10 VVE that harboured the vanA gene and eight that harboured the vanB gene.3Australian Commission on Safety and Quality in Health CareAGAR Sepsis Outcome Programs 2018 Report. Sydney: Australian Commission on Safety and Quality in Health Care.2019https://www.safetyandquality.gov.au/publications-and-resources/resource-library/agar-sepsis-outcome-programs-2018-reportGoogle Scholar Therefore, accurate and timely detection of VVE is imperative in preventing hospital outbreaks and providing effective antibiotic therapy in those with infections. In the index case presented in this article the presence of the vanA gene within the blood culture specimen of this patient was confirmed by real time polymerase chain reaction (PCR)4Merlino J. Kay I.D. Coombs G. Palladino S. Detection of VRE: vanA and vanB genes by PCR.in: Schuller M. Sloots T. James G. Halliday C. Carter I. PCR for Clinical Microbiology. Springer, Dordrecht2010: 415-421Crossref Scopus (2) Google Scholar and by GeneXpert vanA vanB assay (Cepheid, USA). The concurrent presence of the methicillin resistant Staphylococcus aureus isolate was confirmed by PCR in detecting the mecA and femA genes.5Merlino J. Kay I.D. Coombs G. Palladino S. Detection of VRE: vanA and vanB genes by PCR.in: Schuller M. Sloots T. James G. Halliday C. Carter I. PCR for Clinical Microbiology. Springer, Dordrecht2010: 407-414Crossref Scopus (1) Google Scholar Testing of the patient rectal swabs on admission on chromogenic agar (ChromID VRE agar; bioMérieux, Australia), and for several months while hospitalised on screening, did not detect VRE. Phenotypic susceptibility tests were performed on both the VVE and MRSA isolates using Vitek2 XL and Etest (both bioMérieux) and results are shown in Table 1. Both isolates were susceptible to daptomycin, and the patient was treated with daptomycin. Subsequently the VVE was not isolated again from blood cultures or any rectal swabs; however, the MRSA persisted with further positive blood cultures, and the patient was switched to vancomycin after the daptomycin MIC level rose to 4 mg/L on the Vitek2 XL and 2 mg/L by Etest.Table 1Susceptibility profiles (MICs mg/L) of Enterococcus faecium harbouring the vanA gene complex (VVE) and MRSA isolated from the bacteraemiaIsolateVitek2 XLEtestAntibiotics (MICs)PENAMPVANTEICLZDDAPVANDAPTEICVVE≥64≥32≤0.511NT121MRSA>0.5NT≤0.5≤0.52110.51AMP, ampicillin; DAP, daptomycin; LZD, linezolid; MIC, minimum inhibitory concentration; MRSA, methicillin resistant Staphylococcus aureus; NT, not tested; PEN, penicillin; TEC, teicoplanin; VAN, vancomycin; VVE, vancomycin variable enterococci.Vitek 2 XL cards used staphylococci card AST-P656, enterococci card AST-P643. Open table in a new tab AMP, ampicillin; DAP, daptomycin; LZD, linezolid; MIC, minimum inhibitory concentration; MRSA, methicillin resistant Staphylococcus aureus; NT, not tested; PEN, penicillin; TEC, teicoplanin; VAN, vancomycin; VVE, vancomycin variable enterococci. Vitek 2 XL cards used staphylococci card AST-P656, enterococci card AST-P643. VRE resistance in vanA bearing enterococci isolates is typically mediated by the group of genes vanR, vanS, vanH, vanA, and vanX, which are usually carried on the Tn1546 transposon. The expression of these genes leads to replacement of the C-terminal D-Ala residue with D-Lac during cell wall synthesis, thus modifying the vancomycin binding target. The transposon is often located in plasmids, making it easy to transfer among enterococcal strains. The vanA transposon is composed of seven genes including vanR and vanS (which regulate the expression of vancomycin resistance); vanH, vanA, vanX, vanY (vancomycin resistance) and vanZ (teicoplanin resistance). Whole genome sequencing analysis (MiSeq; Illumina, USA) of the VVE isolate isolated from this blood culture specimen revealed that this isolate contained vanR, vanS, vanH and vanA but did not contain vanX, vanY and vanZ. The isolate was multilocus sequenced and was shown to be ST1424. The genome analysis also revealed partial deletion of the vanA gene (83 bp deletion; 92% coverage). This isolate was phenotypically sensitive to vancomycin and teicoplanin. The vancomycin sensitivity may be explained by the partial deletion in the vanA gene or the absence of vanX and vanY, while the teicoplanin sensitivity may be explained by the absence of the vanZ gene (Fig. 1). This bacteraemia case with VVE and MRSA raises several important questions, previously discussed by Downing et al.6Downing M.A. Xiong J. Eshaghi A. McGeer A. Patel S.N. Johnstone J. Vancomycin-variable enterococcal bacteremia.J Clin Microbiol. 2015; 53: 3951-3953Crossref PubMed Scopus (3) Google Scholar Should vancomycin be avoided in patients with serious VVE infections? A patient colonised with this organism was recently described, and it was shown that the isolate developed resistance to vancomycin in vivo during vancomycin therapy.7Coburn B. Low D.E. Patel S.N. et al.Vancomycin-variable Enterococcus faecium: in vivo emergence of vancomycin resistance in a vancomycin-susceptible isolate.J Clin Microbiol. 2015; 52: 1766-1767Crossref Scopus (17) Google Scholar It has been reported that exposure of VVE strains to vancomycin in vitro leads to the development of vancomycin resistance by the constitutive expression of vanHAXYZ gene clusters.8Thaker M. Kalan L. Waglechner N. et al.Vancomycin-variable enterococci can give rise to constitutive resistance during antibiotic therapy.Antimicrob Agents Chemother. 2015; 59: 1405-1410Crossref PubMed Scopus (27) Google Scholar The use of vancomycin to treat VVE infections could provide selective pressure that may lead to the development of therapy induced resistance and treatment failure. Therefore, it would be sensible to avoid the administration of vancomycin to patients infected with VVE strains. Given the introduction of real time PCR in many laboratories, should molecular testing be the standard of care for identifying VVE from all sterile sites as recommended by AGAR (Australian Group Antimicrobial Resistance)? Our laboratory performs vanA/vanB PCR testing of any Enterococcus isolates obtained from a sterile site. Further surveillance data such as those supplied by AGAR are needed to better understand the prevalence of VVE in clinical specimens. If VVE becomes an established nosocomial pathogen, appropriate routine genotypic testing of E. faecium clinical isolates is recommended, particularly those from sterile sites, to determine the presence of vancomycin resistance genes. Should we worry about the colonisation of VVE since the routine non-molecular VRE screening methods do not reliably identify VVE and did not detect the index case summarised here? A large hospital outbreak due to VVE has been previously described in Ontario9Szakacs T.A. Kalan L. McConnell M.J. et al.Outbreak of vancomycin-susceptible Enterococcus faecium containing the wild-type vanA gene.J Clin Microbiol. 2014; 52: 1682-1686Crossref PubMed Scopus (31) Google Scholar and Denmark,2Hammerum A.M. Justesen U.S. Pinholt M. et al.Surveillance of vancomycin-resistant enterococci reveals shift in dominating clones and national spread of a vancomycin-variable vanA Enterococcus faecium ST1421-CT1134 clone, Denmark, 2015 to March 2019.Euro Surveill. 2019; 24: 1-5Crossref Scopus (17) Google Scholar thus highlighting that VVE is able to spread within the community and health care facilities. Further research is required to determine the sensitivity of various selective agars with and without vancomycin in detecting VVE and whether this strategy in combination with molecular testing is cost-effective. We thank Dr Sebastiaan van Hal and Dr Alecia Beukers, Department of Microbiology, Royal Prince Alfred Hospital, Sydney, for performing whole genome sequencing for this isolate. We also thank Denise Daley from AGAR for personal communication. The authors state that there are no conflicts of interest to disclose.