Clonal outbreak of ST17 multidrug-resistant Enterococcus faecium harbouring an Inc18-like::Tn1546 plasmid in a haemo-oncology ward of a Spanish hospital

To report a clonal outbreak of ST17 vancomycin-resistant Enterococcus faecium (VREfm) carrying Tn1546 (vanA) in a haemo-oncology ward of a tertiary teaching hospital in the south of Spain (JanuarySeptember 2009). Twenty-two VREfm strains from 13 patients were characterized by PFGE, multiple-locus variable-number tandem-repeat analysis (MLVA) and multilocus sequence typing (MLST). Genes encoding antibiotic resistance and putative virulence traits and the Tn1546 backbone were investigated by PCR. Plasmid characterization included determination of size (S1-PFGE) and replication modules (PCR, hybridization and sequencing). Patient clinical records were analysed retrospectively. A single ST17 E. faecium clone (MT-7 MLVA type) carrying esp and hyl plus a 30 kb Inc18-like::Tn1546 (IS1216) plasmid was identified. Ampicillin resistance was linked to PBP5 showing mutations at positions 24, 27, 34, 66, 68, 85, 100, 144, 172, 177, 204, 216, 324, 462, 466, 470, 485, 496, 499, 525, 546, 558, 582, 586, 629, 632, 642 and 667. Other resistance genes identified were erm(B), ant(6)-Ia and aph(3)-IIIa. Fluoroquinolone resistance was attributable to ParC (Arg-61Gly and Ser-80Arg) and GyrA (Ser-83Arg) mutations. A nosocomial outbreak caused by an ST17 (CC17) E. faecium clone harbouring Esp and Hyl and a 30 kb Inc18-like::Tn1546 plasmid among haemo-oncology patients is reported. The failure of early infection control practices indicates an undetected reservoir and the ability of this strain to persist over long periods. The potential spread of epidemic clones and broad host plasmids carrying vancomycin resistance in Spain is of concern since it might contribute towards a higher rate of VREfm infection.