Tetracycline Resistance in Chlamydia suis Mediated by Genomic Islands Inserted into the Chlamydial inv -Like Gene

Abstract

ABSTRACT Many strains of Chlamydia suis , a pathogen of pigs, express a stable tetracycline resistance phenotype. We demonstrate that this resistance pattern is associated with a resistance gene, tet (C), in the chlamydial chromosome. Four related genomic islands were identified in seven tetracycline-resistant C. suis strains. All resistant isolates carry the structural gene tet (C) and the tetracycline repressor gene tetR (C). The islands share significant nucleotide sequence identity with resistance plasmids carried by a variety of different bacterial species. Three of the four tet (C) islands also carry a novel insertion sequence that is homologous to the IS 605 family of insertion sequences. In each strain, the resistance gene and associated sequences are recombined into an identical position in a gene homologous to the inv gene of the yersiniae. These genomic islands represent the first examples of horizontally acquired DNA integrated into a natural isolate of chlamydiae or within any other obligate intracellular bacterium.