Plasmid-mediated antimicrobial resistance in motile aeromonads from diseased Nile tilapia (Oreochromisniloticus)

For the sustainable farming of tilapia, proper maintenance of their health and adequate treatment for infections at appropriate time are inevitable. The indiscriminate use of antibiotics in aquaculture, as a part of treatment and as growth promoters, accelerates antimicrobial resistance (AMR) among the fish pathogens. In the present study, we have isolated diverse aeromonads from Nile tilapia and studied their antibiogram and plasmid profiling.Aeromonas hydrophila,Aeromonas veronii,Aeromonas sobria,Aeromonas dhakensis,Aeromonas caviae,Aeromonas jandaeiandAeromonas aquaticawere isolated from infected tilapia (n = 150), and their Shannon wiener diversity index was calculated as 1.926.A. veroniiwas found to be the most multiple antibiotic-resistant pathogen with the MAR index of 0.46, andA. aquaticawas noticed as the least resistant isolate. The minimum inhibitory concentration of resistant antibiotics was shown as >256 mcg/ml for most of the isolates. The virulent genes such as aerolysin and hemolysin were identified in all the isolates exceptA. aquatica. The detection of class 1 integrons, plasmid profiling and plasmid curing studies confirmed that AMR exhibited by most of theAeromonasspecies is of plasmid mediated. This challenges the risk of wide spread of AMR among the pathogens and subsequent treatment of the infection.

Automated summary

The study isolated diverse Aeromonas species from infected Nile tilapia, with A. veronii being the most multiple antibiotic-resistant pathogen and A. aquatica being the least resistant. Most isolates showed a minimum inhibitory concentration of resistant antibiotics >256 mcg/ml, and plasmid-mediated resistance was confirmed among most Aeromonas species. This poses a challenge in the treatment of infections and the risk of widespread antimicrobial resistance among pathogens.