title: Evidence of Increased Antibiotic Resistance in Phylogenetically-DiverseAeromonasIsolates from Semi-Intensive Fish Ponds Treated with Antibiotics.
abstract: The genusAeromonasis ubiquitous in aquatic environments encompassing a broad range of fish and human pathogens.Aeromonasstrains are known for their enhanced capacity to acquire and exchange antibiotic resistance genes and therefore, are frequently targeted as indicator bacteria for monitoring antimicrobial resistance in aquatic environments. This study evaluated temporal trends inAeromonasdiversity and antibiotic resistance in two adjacent semi-intensive aquaculture facilities to ascertain the effects of antibiotic treatment on antimicrobial resistance. In the first facility, sulfadiazine-trimethoprim was added prophylactically to fingerling stocks and water column-associatedAeromonaswere monitored periodically over an 11-month fish fattening cycle to assess temporal dynamics in taxonomy and antibiotic resistance. In the second facility,Aeromonaswere isolated from fish skin ulcers sampled over a 3-year period and from pond water samples to assess associations between pathogenic strains to those in the water column. A total of 1200Aeromonasisolates were initially screened for sulfadiazine resistance and further screened against five additional antimicrobials. In both facilities, strong correlations were observed between sulfadiazine resistance and trimethoprim and tetracycline resistances, whereas correlations between sulfadiazine resistance and ceftriaxone, gentamicin, and chloramphenicol resistances were low. Multidrug resistant strains as well assul1, tetA, andintI1gene-harboring strains were significantly higher in profiles sampled during the fish cycle than those isolated prior to stocking and these genes were extremely abundant in the pathogenic strains. Five phylogenetically distinctAeromonasclusters were identified using partialrpoDgene sequence analysis. Interestingly, prior to fingerling stocking the diversity of water column strains was high, and representatives from all five clusters were identified, including anA. salmonicidacluster that harbored all characterized fish skin ulcer samples. Subsequent to stocking, diversity was much lower and most water column isolates in both facilities segregated into anA. veronii-associated cluster. This study demonstrated a strong correlation between aquaculture,Aeromonasdiversity and antibiotic resistance. It provides strong evidence for linkage between prophylactic and systemic use of antibiotics in aquaculture and the propagation of antibiotic resistance.
authors.affiliation: Institute of Soil, Water and Environmental Sciences, Volcani Center - Agricultural Research Organization Rishon Lezion, Israel.
authors.forename: Hemant J
authors.initials: HJ
authors.lastname: Patil
authors.affiliation: Dor Aquaculture Research Station, Fisheries Department, Israel Ministry of Agriculture and Rural Development Dor, Israel.
authors.forename: Ayana
authors.initials: A
authors.lastname: Benet-Perelberg
authors.affiliation: Dor Aquaculture Research Station, Fisheries Department, Israel Ministry of Agriculture and Rural Development Dor, Israel.
authors.forename: Alon
authors.initials: A
authors.lastname: Naor
authors.affiliation: Central Fish Health Laboratory, Department of Fisheries and Aquaculture, Ministry of Agriculture and Rural Development Nir David, Israel.
authors.forename: Margarita
authors.initials: M
authors.lastname: Smirnov
authors.affiliation: Central Fish Health Laboratory, Department of Fisheries and Aquaculture, Ministry of Agriculture and Rural Development Nir David, Israel.
authors.forename: Tamir
authors.initials: T
authors.lastname: Ofek
authors.affiliation: Institute of Soil, Water and Environmental Sciences, Volcani Center - Agricultural Research Organization Rishon Lezion, Israel.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Nasser
authors.affiliation: Institute of Soil, Water and Environmental Sciences, Volcani Center - Agricultural Research Organization Rishon Lezion, Israel.
authors.forename: Dror
authors.initials: D
authors.lastname: Minz
authors.affiliation: Institute of Soil, Water and Environmental Sciences, Volcani Center - Agricultural Research Organization Rishon Lezion, Israel.
authors.forename: Eddie
authors.initials: E
authors.lastname: Cytryn
keywords: Aeromonas; antibiotic resistance; antibiotic resistance gene; aquaculture; integron