ANTIBIOTIC RESISTANCE ACROSS PHYLOGENETICALLY-DIVERSE AEROMONAS ISOLATES FROM AN EXTENSIVE AQUACULTURE ECOSYSTEM

Aeromonas species are considered to be an emerging threat because of their pathogenic attributes in fish as well as in other hosts including humans. Their substantial capacity to exchange mobile genetic elements that harbor antibiotic resistance genes, make this genus a hotspot for exchange of antibiotic resistance genes. This study evaluated antibiotic resistance in a large collection of Aeromonas isolates from extensive aquaculture pools from a semi-closed aquaculture research facility. Out of total 97 isolates screened against seven different antibiotic compounds, various levels of resistance were observed. The majority of the isolates were resistant to ampicillin (90%) followed by sulfadiazine (89%), trimethoprim (36%) and ceftriaxone (28%). Thirty four percent of the Aeromonas isolates were resistant to 2 of the screened antibiotics, while 21% and 22% were resistant to four and five antibiotics, respectively. Clustering based on 16S-rRNA and rpoD genes revealed that the isolates grouped within several distinct Aeromonas clusters. Interestingly, multidrug resistance was observed in the isolates associated with Aeromonas hydrophila and Aeromonas salmonicida, which are common fish and human pathogens. Out of 33 partially characterized Aeromonas isolates, the majority harbored intI1 (52%) and several contained the clinically-associated ESBL genes bla_CTX-M (24%) and bla_OXA (12%). The high multidrug resistance and significant presence of antibiotic resistance genes in the Aeromonas spp. isolated from the extensive aquaculture system is cause for alarm given the capacity of these bacteria to serve as an interface for potential transfer of antibiotic resistance to other bacteria in aquaculture and in downstream environments.