ccrABEnt serine recombinase genes are widely distributed in the Enterococcus faecium and Enterococcus casseliflavus species groups and are expressed in E. faecium

The presence, distribution and expression of cassette chromosome recombinase (ccr) genes, which are homologous to the staphylococcal ccrAB genes and are designated ccrAB(Ent) genes, were examined in enterococcal isolates (n=421) representing 13 different species. A total of 118 (28%) isolates were positive for ccrAB(Ent) genes by PCR, and a number of these were confirmed by Southern hybridization with a ccrA(Ent) probe (n=76) and partial DNA sequencing of ccrA(Ent) and ccrB(Ent) genes (n=38). ccrAB(Ent) genes were present in Enterococcus faecium (58/216, 27%), Enterococcus durans (31/38, 82%), Enterococcus hirae (27/52, 50%), Enterococcus casseliflavus (1/4, 25%) and Enterococcus gallinarum (1/2, 50%). In the eight other species tested, including Enterococcus faecalis (n=94), ccrAB(Ent) genes were not found. Thirty-eight sequenced ccrAB(Ent) genes from five different enterococcal species showed 94-100% nucleotide sequence identity and linkage PCRs showed heterogeneity in the ccrAB(Ent) flanking chromosomal genes. Expression analysis of ccrAB(Ent) genes from the E. faecium DO strain showed constitutive expression as a bicistronic mRNA. The ccrAB(Ent) mRNA levels were lower during log phase than stationary phase in relation to total mRNA. Multi locus sequence typing was performed on 39 isolates. ccrABEnt genes were detected in both hospital-related (10/29, 34%) and non-hospital (4/10, 40%) strains of E. faecium. Various sequence types were represented by both ccrAB(Ent) positive and negative isolates, suggesting acquisition or loss of ccrAB(Ent) in E. faecium. In summary, ccrAB(Ent), genes, potentially involved in genome plasticity, are expressed in E. faecium and are widely distributed in the E. faecium and E. casseliflavus species groups.