Diversity and Evolution of the Tn5801-tet(M)-Like Integrative and Conjugative Elements among Enterococcus, Streptococcus, and Staphylococcus
This work describes the diversity and evolution of Tn5801among enterococci, staphylococci, and streptococci based on analysis of the 5,073 genomes of these bacterial groups available in gene databases. We also examined 610 isolates ofEnterococcus(from 10 countries, 1987 to 2010) for the presence of this and other known CTn-tet(M) elements due to the scarcity of data about Tn5801among enterococci. Genome location (by ICeu-I–pulsed-field gel electrophoresis [PFGE] hybridization/integration site identification), conjugation and fitness (by standard methods), Tn5801characterization (by long-PCR mapping/sequencing), and clonality (by PFGE/multilocus sequence typing [MLST]) were studied. Twenty-three Tn5801variants (17 unpublished) clustered in two groups, designated “A” (25 kb;n= 14; predominant inStaphylococcus aureus) and “B” (20 kb;n= 9; predominant inStreptococcus agalactiae). The percent GC content of the common backbone suggests a streptococcal origin of Tn5801group B, with further acquisition of a 5-kb fragment that resulted in group A. Deep sequence analysis allowed identification of variants associated with clonal lineages ofS. aureus(clonal complex 8 [CC8], sequence type 239 [ST239]),S. agalactiae(CC17),Enterococcus faecium(ST17/ST18), orEnterococcus faecalis(ST8), local variants, or variants located in different species and geographical areas. All Tn5801elements were chromosomally located upstream of theguaAgene, which serves as an integration hot spot. Transferability was demonstrated only for Tn5801type B amongE. faecalisclonal backgrounds, which eventually harbored another Tn5801copy. The study documents early acquisition of Tn5801byEnterococcus,Staphylococcus, andStreptococcus. Clonal waves of these pathogens seem to have contributed to the geographical spread and local evolution of the transposon. Horizontal transfer, also demonstrated, could explain the variability observed, with the isolates often containing sequences of different origins.