Isolation, identification and molecular characterization of Aeromonas spp. from farmed loach (Misgurnus anguillicaudatus)

Gram-negative Aeromonas bacteria is known to contaminate aquaculture products and retains the ability to infect wide range of host including fishes, shrimps and humans. This study is designed to evaluate the presence of Aeromonas in healthy loaches (Misgurnus anguillicaudatus) collected from the markets in Hainan and Guangdong provinces of China. Based on the molecular sequencing and phylogenetic analysis with single 16S rRNA and concatenated genes (gyrA and ropD), 104 isolates were identified as Aeromonas species followed by further classification to A. veronii (83.65%), A. jandaei (9.62%), A. hydrophila (3.85%) and A. allosaccharophila (2.88%). More than half of the isolates displayed hemolytic activity of 87.5% and were able to form moderate biofilm (78.26%). Fourteen antibiotics from ten representative classes were screened that demonstrated complete resistance to ampicillin, 89.4% and 68.3% to lincomycin and nalidixic acid. Moreover, a notable detection and prevalence was found in screening of ten virulence-related and nine resistance genes. To our knowledge, it is the first report of its kind demonstrating potential threat of the commercial loaches carrying Aeromonas to human health. These findings will assist professionals working in clinical settings to optimize their prescription accordingly and researchers to access the impacts of Aeromonas resistance on human health. ImportanceThis study demonstrates high infection rate of loaches by Aeromonas spp. in Hainan and Guangdong provinces of China. The most prevalent species was Aeromonas veronii. Most of the isolates displayed hemolytic activity and formed moderate biofilm. Multiple virulence genes, resistance genes and multi-antibiotic resistance were detected. Aeromonads risks should be considered in loach industry.