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Hospital outbreak of vancomycin-resistant enterococci caused by a single clone of Enterococcus raffinosus and several
M Kawalec1, J Kedzierska, A Gajda
1National Medicines Institute, Warsaw, Poland. madziak@cls.edu.pl
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.
Insights
A hospital vancomycin-resistant Enterococcus outbreak involved Enterococcus raffinosus and Enterococcus faecium. Misidentification of E. raffinosus highlights challenges in vancomycin-resistant enterococci (VRE) control strategies.
Area of Science:
- Microbiology
- Infectious Diseases
- Clinical Epidemiology
Background:
- Vancomycin-resistant enterococci (VRE) pose a significant healthcare challenge.
- Mixed outbreaks of VRE require detailed molecular investigation for effective control.
- Enterococcus raffinosus and Enterococcus faecium are common VRE species.
Purpose of the Study:
- To analyze a mixed VRE outbreak caused by E. raffinosus and E. faecium in a Polish hospital.
- To investigate the molecular epidemiology and genetic relatedness of the VRE isolates.
- To assess the role of E. raffinosus misidentification in VRE control.
Main Methods:
- Multilocus sequence analysis (MLSA) for unambiguous identification of Enterococcus species.
- Molecular typing to determine clonal or polyclonal nature of isolates.
- Plasmid analysis to identify genetic elements responsible for vancomycin resistance.
Main Results:
- A mixed outbreak involved 27 patients across three hospital wards, including haematology.
- E. raffinosus isolates, initially misidentified, showed high-level multiresistance and a clonal outbreak pattern.
- E. faecium isolates exhibited a polyclonal structure, with one clone likely originating from endemic hospital strains.
- All isolates shared a vanA gene on a similar conjugative plasmid (Tn1546-like element).
Conclusions:
- Misidentification of E. raffinosus can lead to underestimation of its role in VRE outbreaks.
- Effective VRE control strategies must account for accurate identification of all relevant Enterococcus species.
- The study underscores the importance of molecular methods in understanding VRE epidemiology and transmission.
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