Abstract
Aeromonas is regarded as an important pathogen of freshwater animals but little is known about the genetics of its antimicrobial resistance in Chinese aquaculture. The aim of this study was to investigate the presence of integrons and characterize multidrug resistant Aeromonas spp. isolated from diseased farmed freshwater animals. These animal samples included fish, ornamental fish, shrimp, turtles, and amphibians which were collected from 64 farms in Guangdong province of South China. One hundred and twelve Aeromonas spp. isolates were examined for antimicrobial resistance phenotypes and the presence of class 1 integron sequences. Twenty-two (19.6%) of these isolates carried a class 1 integron comprising six different gene insertion cassettes including drfA12-orfF-aadA2, drfA12-orfF, aac(6′)-II-blaOXA-21-cat3, catB3, arr-3, and dfrA17. Among these, drfA12-orfF-aadA2 was the dominant gene cassette array (63.6%, 14/22) and this is the first report of aac(6′)-II-blaOXA-21-cat3 in an Aeromonas hydrophila isolate from a Chinese giant salamander (Andrias davidianus). All the integron-positive strains were resistant to more than five agents and 22 contained other resistance genes including blaCTX-M-3, blaTEM-1, aac(6′)-Ib-cr, and tetA. All integron-positive isolates also contained mutations in the quinolone resistance determining regions (QRDR). Our investigation demonstrates that freshwater animals can serve as a reservoir for pathogenic Aeromonas strains containing multiple drug-resistance integrons. This data suggests that surveillance for antimicrobial resistance of animal origin and a prudent and responsible use of antimicrobials in aquaculture is necessary in these farms.
Highlights
The genus Aeromonas is regarded as an important pathogen of freshwater animals
Base on the biochemical and genetic characteristics, 112 Aeromonas isolates were identified up to the species level. They belonged to eight different species of Aeromonas (A. hydrophila, A. veronii, A. caviae, A. sobria, A. dhakensis, A. jandaei, A. trota, and A. media; Table 1)
Among 112 Aeromonas strains isolated from different farmed freshwater animals, 22 (19.6%) isolates were positive for intI1 while intI2 and intI3 were not detected in any of the isolates
Summary
The genus Aeromonas is regarded as an important pathogen of freshwater animals. Motile aeromonads including A. hydrophila, A. veronii, A. caviae, and A. sobria are considered facultative pathogens and can infect fish as well as shrimp, reptiles, amphibians, and other aquatic species (Janda and Abbott, 2010). Treatment and prevention of diseases in animal husbandry including livestock and aquaculture have been relying on the extensive use of antimicrobials. This practice has been undoubtedly increased the frequency of antibiotic-resistant bacterial strains and this has been widely documented. Antimicrobial resistance in bacterial populations can result from clonal selection under antimicrobial selective pressure or through horizontal gene transfer. Mobile genetic elements such as plasmids, integrons, and transposons contribute to a wider dissemination of genetic resistance determinants among bacteria (Boerlin and Reid-Smith, 2008). The most often found resistance gene cassettes contained several aminoglycoside resistance gens aadA1, aadA2, and the trimethoprim resistance gene dfrA1 (Piotrowska and Popowska, 2015)
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