Prevalence, Virulence Gene Distribution and Alarming the Multidrug Resistance of Aeromonas hydrophila Associated with Disease Outbreaks in Freshwater Aquaculture.

Doan Thi Nhinh,Lua Thi Dang,Truong Dinh Hoai,Kim Van Van,Nguyen Thi Huong Giang,Dung Viet Le

doi:10.3390/antibiotics10050532

Abstract

The study aims to evaluate the infection prevalence, virulence gene distribution and antimicrobial resistance of Aeromonas hydrophila associated in diseased outbreaks of cultured freshwater fish in Northern Vietnam. The confirmed A. hydrophila were screened for the presence of the five pitutative-virulence genes including aerolysin (aerA), hemolysin (hlyA), cytotonic enterotoxin (act), heat-labile cytotonic enterotoxin (alt), and heat-stable enterotoxin (ast), and examined the susceptibility to 16 antibiotics. A total of 236 A. hydrophila isolates were recovered and confirmed from 506 diseased fish by phenotypic tests, PCR assays, and gyrB, rpoB sequenced analyses, corresponding to the infection prevalence at 46.4%. A total of 88.9% of A. hydrophila isolates harbored at least one of the tested virulence genes. The genes aerA and act were most frequently found (80.5% and 80.1%, respectively) while the ast gene was absent in all isolates. The resistance to oxacillin, amoxicillin and vancomycin exhibited the highest frequencies (>70%), followed by erythromycin, oxytetracycline, florfenicol, and sulfamethoxazole/trimethoprim (9.3–47.2%). The multiple antibiotic resistance (MAR) index ranged between 0.13–0.88 with 74.7% of the isolates having MAR values higher than 0.2. The results present a warning for aquaculture farmers and managers in preventing the spread of A. hydrophila and minimizing antibiotic resistance of this pathogen in fish farming systems.

Highlights

Freshwater fish farming represents a substantial proportion in the aquaculture industry, in developing countries providing food and livelihood and contribution to the regional economy [1]
46.4% of diseased fish with the typical hemorrhagic septicemia symptoms were infected with A. hydrophila, which reveals the predominance of this pathogen in freshwater fish farming in Northern Vietnam and constitutes a huge economic loss due to the high accumulative mortality of fish in impacted ponds/cages
The results suggest for these isolates the possible involvement of other virulence genes and pathogenic factors not investigated in this study, such as genes encoding proteases and lipase, in inducing hemorrhagic septicemia symptoms in diseased fish [34,48], or the concurrence of infection with other pathogens [49]

Summary

Introduction

Freshwater fish farming represents a substantial proportion in the aquaculture industry, in developing countries providing food and livelihood and contribution to the regional economy [1]. Aeromonas spp. are commonly found in freshwater, estuarine, and saltwater environments [6,7,8]. Members of this genus have been the focus of attention because of their potential to act as pathogens on a wide range of hosts in fish, amphibians, and reptiles and in mammals, including humans [8,9]. Among Aeromonas species that cause fish diseases, A. hydrophila has been identified as one of the most dangerous pathogens causing mortality outbreaks in a diversity of cultured fish species [6,10] and has been responsible for huge economic losses in various countries [11,12]

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