Abstract
The genus Aeromonas is ubiquitous in aquatic environments encompassing a broad range of fish and human pathogens. Aeromonas strains 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 in Aeromonas diversity 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-associated Aeromonas were monitored periodically over an 11-month fish fattening cycle to assess temporal dynamics in taxonomy and antibiotic resistance. In the second facility, Aeromonas were 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 1200 Aeromonas isolates 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 as sul1, tetA, and intI1 gene-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 distinct Aeromonas clusters were identified using partial rpoD gene sequence analysis. Interestingly, prior to fingerling stocking the diversity of water column strains was high, and representatives from all five clusters were identified, including an A. salmonicida cluster 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 an A. veronii-associated cluster. This study demonstrated a strong correlation between aquaculture, Aeromonas diversity and antibiotic resistance. It provides strong evidence for linkage between prophylactic and systemic use of antibiotics in aquaculture and the propagation of antibiotic resistance.
Highlights
Aeromonas spp. are Gram negative, facultative anaerobic, nonspore forming rods that often inhabit water and soil habitats (Martin-Carnahan and Joseph, 2005)
We analyzed 17 fish skin ulcer isolates acquired from 15 independent samples from the Madan aquaculture facility sampled from 2013 to 2015 as a taxonomic marker of prominent Aeromonas fish pathogens in the region
This study comprehensively assessed diversity, antibiotic resistance, and presence of selected Antibiotic resistance genes (ARG) in a large collection of Aeromonas strains isolated from commercial earthen pond aquaculture facilities
Summary
Aeromonas spp. are Gram negative, facultative anaerobic, nonspore forming rods that often inhabit water and soil habitats (Martin-Carnahan and Joseph, 2005). They are commonly isolated from food, invertebrates, plants, and animals (Araujo et al, 2002; Janda and Abbott, 2010; Joseph et al, 2013). Comprehensive phylogenetic classification of Aeromonas strains is critical in view of their clinical and ecological importance (Colston et al, 2014), but the genus Aeromonas has been found to be taxonomically challenging due to the occurrence of microheterogeneities in the 16S rRNA gene (Alperi et al, 2008). Most often Aeromonas salmonicida and A. hydrophila are known to cause ulcerative and hemorrhagic skin ulcers (Igbinosa et al, 2012) in fish under stress, which is often associated with poor sanitation and nutritional deficiencies (Noga, 2011)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
