Abstract
The emergence of antimicrobial-resistant bacteria is an enormous challenge to public health. Aeromonas hydrophila and Aeromonas veronii 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 Aeromonas 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 Aeromonas spp. isolated from aquatic animals. Results showed that 89.2% of A. hydrophila and 75.8% of A. veronii isolates were non-wild types according to the oxytetracycline ECVCLSI and ECVNRI, respectively. The antimicrobial resistance genes included tetA, tetB, tetD, tetE, cat, floR, qnrA, qnrB, qnrS, strA-strB, and aac(6′)-1b. The most common tet gene in Aeromonas spp. isolates was tetE, followed by tetA. Some strains carried more than one tet gene, with tetA–tetD and tetA–tetE found in A. hydrophila; however, tetB was not detected in any of the strains. Furthermore, 18.6% of A. hydrophila and 24.2% of A. veronii 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.
Highlights
The genus Aeromonas comprises 36 species representing ubiquitous bacteria isolated from food, animal, and aquatic environments [1]
MICs obtained for Aeromonas spp. isolates ranged from 0.25–64 μg mL−1 for doxycycline, 0.03–32 μg mL−1 for enrofloxacin, and 0.03–64 μg mL−1 for erythromycin and florfenicol
This study showed that 89.2% of A. hydrophila could be categorized as non-wild type (NWT) upon applying an oxytetracycline ECVCLSI of 0.25 μg mL−1 ; 75.8% of A. veronii were determined as NWT upon applying an oxytetracycline ECVNRI of 0.5 μg mL−1
Summary
The genus Aeromonas comprises 36 species representing ubiquitous bacteria isolated from food, animal, and aquatic environments [1]. Aeromonas is an enteric pathogen, which causes haemorrhagic septicaemia, fin rot, and soft-tissue rot companied by high mortality [2,3]. Aeromonas spp. produce a variety of toxins, including hemolysins, aerolysins, and cytotonic enterotoxins, which cause diarrhea, enteritis, and dysentery [4,5]. Aeromonas spp. are opportunistic bacteria commonly present in freshwater and marine environments, with Aeromonas salmonicida subsp. Salmonicida, Aeromonas hydrophila, and Aeromonas veronii identified as causative agents of hemorrhagic skin ulcers and furunculosis in Nile tilapia, common carp, and channel catfish [1,6–9]. Pathogenic Aeromonas spp. kills 80–100% of commercial carp within 1–2 weeks, resulting in the deterioration of production quality in fisheries [10]. The resulting unfavorable conditions, such as hypoxia or nitrogen-waste accumulation, induce a significant reduction in immune response leading to increased risk of pathogen translocation, infection, and disease [11]. The resulting unfavorable conditions, such as hypoxia or nitrogen-waste accumulation, induce a significant reduction in immune response leading to increased risk of pathogen translocation, infection, and disease [11]. β-lactam-, aminoglycoside-, and quinolone-resistant strains of Aeromonas spp
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