Evolution of trimethoprim/sulfamethoxazole resistance in Shewanella algae from the perspective of comparative genomics and global phylogenic analysis

Shewanella algae is a zoonotic marine bacterium that causes a variety of infections in immunocompromised patients or those who have been exposed to seawater. The development of trimethoprim/sulfamethoxazole (TMP/SMX) resistance in S. algae are found in human and environment isolates during the past ten years, and thus the treatment options are decreasing. In the study, we conduct a comparative genomic study to identify the resistant mechanism of TMP/SMX-resistance in S. algae. We found the resistance of TMP/SMX in S. algae is associated with the existence of sul1 and dfrA12 within the class 1 integron. The gene cassette dfra12-aadA2-qacEΔ1/sul1 within the class 1 integron is highly conserved. In addition, the class 1 integron and encapsulated sul1 are significantly enriched in Enterobacteriaceae in NCBI and UniProt databases. Our study suggests that the horizontal transfer of TMP/SMX resistance via class 1 integron is most frequently occurred within Enterobacteriaceae and has spread to a wide range of sources including soil, poultry, and marine water.