Establishment of Epidemiological Cut-Off Values and the Distribution of Resistance Genes in Aeromonas hydrophila and Aeromonas veronii Isolated from Aquatic Animals

Abstract

The emergence of antimicrobial-resistant bacteria is an enormous challenge to public health. <i>Aeromonas hydrophila</i> and <i>Aeromonas veronii</i> are opportunistic pathogens in fish. They exert tremendous adverse effects on aquaculture production, owing to their acquired antibiotic resistance. A few Clinical and Laboratory Standards Institute (CLSI) epidemiological cut-off values (ECVs) against <i>Aeromonas</i> spp. are available. We evaluated antimicrobial susceptibility by establishing 8 ECVs using two analytical methods, normalized resistance interpretation and ECOFFinder. We detected antimicrobial resistance genes in two motile <i>Aeromonas</i> spp. isolated from aquatic animals. Results showed that 89.2% of <i>A. hydrophila</i> and 75.8% of <i>A. veronii</i> isolates were non-wild types according to the oxytetracycline ECV_CLSI and ECV_NRI, respectively. The antimicrobial resistance genes included <i>tetA</i>, <i>tetB</i>, <i>tetD</i>, <i>tetE</i>, <i>cat</i>, <i>floR</i>, <i>qnrA</i>, <i>qnrB</i>, <i>qnrS</i>, <i>strA-strB</i>, and <i>aac(6')-1b</i>. The most common <i>tet</i> gene in <i>Aeromonas</i> spp. isolates was <i>tetE</i>, followed by <i>tetA</i>. Some strains carried more than one <i>tet</i> gene, with <i>tetA</i>-<i>tetD</i> and <i>tetA</i>-<i>tetE</i> found in <i>A. hydrophila</i>; however, <i>tetB</i> was not detected in any of the strains. Furthermore, 18.6% of <i>A. hydrophila</i> and 24.2% of <i>A. veronii</i> isolates showed presumptive multidrug-resistant phenotypes. The emergence of multidrug resistance among aquatic aeromonads suggests the spread of drug resistance and difficult to treat bacterial infections.