Hospital outbreak of vancomycin-resistant enterococci caused by a single clone of Enterococcus raffinosus and several clones of Enterococcus faecium

Abstract

A mixed outbreak caused by vancomycin-resistant Enterococcus raffinosus and Enterococcus faecium carrying the vanA gene was analysed. The outbreak occurred in a large hospital in Poland and affected 27 patients, most of whom were colonised, in three wards, including the haematology unit. The E. raffinosus isolates had a high-level multiresistant phenotype and were initially misidentified as Enterococcus avium; their unambiguous identification was provided by multilocus sequence analysis. The molecular investigation demonstrated the clonal character of the E. raffinosus outbreak and the polyclonal structure of the E. faecium isolates. All of the isolates carried the same Tn1546-like element containing an IS1251-like insertion sequence, located on a c. 50-kb conjugative plasmid. One of the E. faecium clones, found previously to be endemic in the hospital, was probably the source of the plasmid. The results of the study suggest that difficulties in identification may have led to an underestimate of the importance of E. raffinosus in vancomycin-resistant enterococci (VRE) control strategies.

Diversity of Tn 1546 and Its Role in the Dissemination of Vancomycin-Resistant Enterococci in Portugal

“…Horizontal transfer of conjugative plasmids containing Tn1546 seems to have played a relevant role in the recent increase of VRE in Portugal, as vanA was plasmid located in most VRE isolates studied and specific plasmids containing the most prevalent Tn1546 variants were identified in representative distinct clones collected from different cities and years (13). Nevertheless, the role of prevalent and persistent E. faecalis and E. faecium strains in the maintenance of the resistance by acquiring different genetic elements must not be underestimated, highlighting the complex epidemiology associated with successful spread of multidrug-resistant enterococci, as illustrated in Poland and the United States, where both successful plasmids and prevalent clones contributed to endemicity (11,21,22). Plasmid persistence has been described in areas with both high and low antibiotic selective pressure, as in the United States versus Norway or Denmark, suggesting that factors other than antibiotic pressure might be important in VRE maintenance and epidemiology (17,20).…”

Current Trends of Emergence and Spread of Vancomycin-Resistant Enterococci

“…Countries experiencing problems with increasing or significant higher rates of VRE always report about vancomycin-resistant E. faecium. Infections with members of other enterococcal species remain rare although also outbreaks with vanA/B-type resistant E. faecalis, E. raffinosus or VanC-type E. gallinarum were reported (Foglia et al, 2003;Kawalec et al, 2007;Neves et al, 2009;Shirano et al, 2010). In conclusion, the problem of VRE is mainly an issue of vanA-type vancomycin-resistant E. faecium (see the following).…”

“…Increased VRE prevalence is partly associated with spread of single, distinct epidemic clones or types (Klare et al, 2005;Top et al, 2007;Bonora et al, 2007;Werner et al, 2007c;Valdezate et al, 2009;Zhu et al, 2010;Johnson et al, 2010;Hsieh et al, 2010). In contrast, VRE outbreaks in single centres tend to be polyclonal suggesting a diverse population of hospital-acquired E. faecium strains and a highly mobile resistance determinant capable of spreading widely among suitable recipient strains (Yoo et al, 2006;Deplano et al, 2007;Kawalec et al, 2007;Borgmann et al, 2007;Werner et al, 2007c;Hsieh et al, 2009). Many facets of VRE and vancomycin resistance epidemiology are currently not fully understood and the question why vancomycin resistance is still mainly limited to E. faecium remains mainly unanswered (Garcia-Migura et al, 2007;Garcia-Migura et al, 2008;Werner et al, 2010b).…”

Typing of Enterococcus spp. strains in 4 hospitals in the Małopolska region in Poland

“…8,23,24 In Małopolska, in recent years, the presence of both VanA and VanB phenotypes has been described. [25][26][27] All VREfm strains isolated in this study were MDR and this is a problem for the therapeutic management of patients. The most important problem with the multidrug resistance of the studied strains is that they are able to easily acquire (by plasmids and/or transposon transfer) new resistance traits between enterococci.…”