Prevalence, virulence-related genes and antimicrobial resistance of Aeromonas spp. from loach Misgurnus anguillicaudatus with skin ulcer and healthy controls in Southern China

Aeromonas are primarily inhabitants of the aquatic environment, but they can also be isolated from soil, vertebrates and invertebrates. They have been identified as important pathogens in fish and are considered to be emerging pathogens in humans, causing enteric and extraintestinal diseases. The pathogenic factors associated with Aeromonas are multifactorial, involving structural components, secretion systems, quorum sensing, metal ions, extracellular enzymes and exotoxins. Aeromonas pathogenic mechanisms are complex and not well understood. In this study, we investigated the prevalence and diversity of Aeromonas species from loach with skin ulcers and healthy controls in southern China and characterized their virulence profile, antibiotic resistance and biofilm formation. A total of 104 Aeromonas strains were isolated and confirmed at the species level using housekeeping genes gyrA and rpoD and all 104 isolates were identified as: 83% of Aeromonas veronii (n = 87), 10% of Aeromonas jandaei (n = 10), 4% of Aeromonas hydrophila (n = 4), 3% of Aeromonas allosaccharophila (n = 3). Only one isolate carried all 10 virulence genes tested, while at least 3 of these genes were present in all 104 isolates. The 10 virulence genes are present in the following proportions: 64% of hlyA, 67% of ascV, 74% of aexT, 100% of aer, 98% of act, 19% of ast, 41% of alt, 56% of lip,65% of ela, 89% of fla. There are multiple combinations of virulence genes in different strains of the same species. The high prevalence of these virulence factors, even in healthy loach isolates, suggests potential pathogenicity. Furthermore, Aeromonas isolates exhibited high levels of resistance to lincomycin, nalidixic acid, ampicillin-sulbactam, erythromycin and imipenem; however, none were resistant to aztreonam. The incidence of multiple antibiotic resistance (MAR) in Aeromonas isolates was 89.4%. These isolates have a variety of resistance gene profiles, among which CphA, qnrS, sul1 and tem are the most common. Our data suggest that antimicrobial resistance in Aeromonas species of loach origin is mainly due to a wide range of acquired genes. Additionally, all the isolates formed weak biofilm or moderate biofilms in microtiter plates. The capability of such isolates to form biofilms may lead to difficulties in the treatment and control of Aeromonas-related infections. In summary, this study provides valuable data on the species prevalence, virus-related genes, antibiotic resistance, and biofilm formation of Aeromonas in diseased and healthy loaches. It will contribute to the understanding of the interaction between Aeromonas and animals and disease control.

Automated summary

This study investigated the prevalence and characteristics of Aeromonas in loaches in southern China, including their virulence factors, antibiotic resistance, and biofilm formation. The results showed that Aeromonas isolates had diverse combinations of virulence genes, high levels of resistance to antibiotics, and the ability to form biofilms.