High prevalence of class 1 integrase and characterization of class 1 integron gene cassettes in multiresistant bacteria isolated from the gut microbiota of extended antibiotic treated Salmo salar fish farms

• Main Authors: Vásquez-Ponce, F., Higuera-Llantén, S., Cortés, J., Zimin-Veselkoff, N., Marshall, S.H., Mardones, F.O., Olivares-Pacheco, J.
• Format: Report
• Language: English
• Published: 2024
• Subjects: 570; Biología; Salmo salar
• Online Access: https://repositorio.uc.cl/handle/11534/82435; https://doi.org/10.1101/532663

The use of antimicrobials in aquaculture is a common practice. Chile is second larger producer of salmon worldwide, but unfortunately is the first consumer of antibiotics. Tonnes of florfenicol and oxytetracycline yearly are used in the Chilean salmoniculture to control the pathogens that threaten the sustainability of the industry. This excessive use of antibiotics have selected populations of resistant bacteria from the sediments and the water column that sorround the fish farms. In a recent work, our lab described the high prevalence of multiresistant bacteria and Antibiotic Resistance Genes (ARGs) in the gut microbiota of Antlactic salmon (Salmo salar) treated with high doses of antibiotics. In this work, we revisited the analysis of the previously described gut multiresistant bacteria grouped in banks of florfenicol resistant isolates (FB) and oxytetracycline resistant isolates (OB) looking for the presence of integron-integrase elements. These elements have been described as an important players in the Antimicrobial Resistance (AMR) phenomenon and they are considered a good markers of the anthopogenic activities pollution. The results showed that the 100% of the multiresistant isolates present the class 1 intagrase. Despite this result, no isolate from FB showed the typical structure of class 1 integrons: the presence in 3’-CS of qacEΔ1/sul1 genes. While in OB, only 23% of the isolates showed this characteristic structure. Additionally, only four isolates of OB and none of FB showed recognisable gene cassettes and no genes of resistance to florfenicol and oxytetacycline appeared in them. Of these four isolates, three of them showed a single gene cassette containing the dfrA-14 gene, which confers resistance to trimethoprim. Whilst the other isolate showed the aac(6’)31-qacH-blaoxa2 genes, which confers resistance to aminoglycosides, quaternary ammonium compounds and beta-lactams, respectively. Finally, it was possible to demonstrate that the described integrons probably come from anthropogenic activities ...