Differences in tetracycline-resistance determinants carriage among Shigella flexneri and Shigella sonnei are not related to different plasmid Inc-type carriage

The aim of this study was to establish the different prevalence of the most common molecular mechanisms involved in tetracycline resistance as well as their relationship with plasmid incompatibility groups in a collection of Shigella spp. causing traveler's diarrhea. Tetracycline susceptibility was established in 187 Shigella spp. (74S. flexneri and 113S. sonnei). Of these, 153 isolates were recovered as a confirmed cause of traveler's diarrhea. The prevalence of the tet(A), tet(B) and tet(G) genes was analyzed by PCR. A total of 18 plasmid incompatibility groups were determined in a subset of 63 isolates. One hundred twenty-four out of 154 (80.5%) tetracycline-resistant isolates presented at least tet(A) or tet(B). The tet(B) gene was the most frequently detected being present in 70 isolates (45.5%), while the tet(A) gene was detected in 57 (37.0%). The tet(G) gene was only present in 11 (7.2%). In addition, the tet(A) gene was more frequent in S. sonnei (p=0.0007), while the tet(B) gene was more frequent in S. flexneri (p <0.0001). The plasmids belonging to incompatibility group B (p <0.05) were significantly more frequent among S. flexneri, while those belonging to groups K, FIC, and FIIA (p <0.05) were preferentially detected among S. sonnei. The prevalence of the tet(A) and tet(B) genes differs between S. sonnei and S. flexneri. Also, the prevalence of plasmid incompatibility groups in S. flexneri and S. sonnei differs. Nonetheless no relationship was found between the two phenomena