AME 79:197-207 (2017)  -  DOI: https://doi.org/10.3354/ame01828

ABSTRACT: A large collection of aquatic Aeromonas obtained from the surfaces of 5 species of fish in 2 streams with different contamination histories were examined to test hypotheses on the effects of contaminant history, stream habitat and longitudinal location on the incidence of antibiotic resistance (AR) towards 6 antibiotics and levels of multiple antibiotic resistance (MAR). Fish species included an open-water species (Micropterus salmoides), 2 mid-water species of centrarchids (Lepomis auritus and L. punctatus) and 2 species of bottom-dwelling fish (Ameiurus natalis and A. platycephalus). Metal analysis of the sediments indicated that there was a strong downstream contamination gradient in one stream but not in the other. However, we found that the average MAR level was similar between the 2 streams. Comparisons among fish species found the highest levels of resistance in bacteria isolated from bottom-dwelling fish in the least-contaminated stream. However, there were clear differences in levels of resistance between bacteria isolated from the 2 bottom-dwelling fish, with those isolated from A. natalis having significantly higher levels than those isolated from A. platycephalus. We suggest that these differences relate to higher concentrations of metals and other contaminants in habitats where A. natalis is normally found. For some antibiotics, there was a clear pattern of decreasing resistance among bacteria isolated from bottom-dwelling, mid-water and open-water fish. Unlike culturable sediment bacteria from the same streams in previous studies, these commensal aeromonads did not show the same expected patterns of increasing antibiotic resistance in metal-contaminated vs. uncontaminated streams.

KEY WORDS:  Antibiotic resistance · Aeromonas · Commensal · Fish · Industrial pollution · Habitat partitioning