Solation, identification, drug sensitivity characteristics and biological analysis of pathogenic Aeromonas caviae in Monopterus albus

Monopterus albus is renowned for its tender, delectable flesh and exceptional nutritional profile. It is particularly rich in essential fatty acids like DHA and EPA, and possesses significant medicinal properties, including anti-aging and blood lipid regulation, alongside considerable economic value.With the growing demand for M.albus, the continuous expansion and intensification of artificial cultivation, coupled with ongoing changes in the external environment, M.albus is highly susceptible to infections by bacteria, viruses, parasites, and fungi. Diseases caused by bacterial infections have inflicted substantial losses on M.albus farming.Aeromonas caviae is a common zoonotic pathogen that infects humans, animals, and fish. It is widely distributed in various aquatic environments and tends to cause infections and multiple complications in hosts with compromised immunity.To investigate the pathogenic agents and prevention/control methods for the hemorrhagic symptoms on the body surface and visceral organs of diseased M. albus in a farming base in Jingzhou City, Hubei Province.In this study, a dominant bacterial strain was isolated from the lesioned tissues of M. albus. Its biological characteristics were systematically analyzed through morphological observation, physiological and biochemical identification, 16S rRNA gene sequencing, multilocus sequence typing (MLST) analysis, antimicrobial susceptibility testing, pathogenicity assays, and resistance gene sequencing. The isolated strain is a Gram-negative short bacillus. 16S rRNA gene sequencing results confirmed that the isolate is A.caviae derived from M. albus, designated as Ac240602.The isolated strain Ac240602 exhibits β-hemolytic activity, and its molecular typing is ST 2615.The artificially infected M. albus showed swelling of the skin and anus, as well as varying degrees of hemorrhage in the liver, intestines, spleen, and kidneys, which were similar to the symptoms of naturally infected cases.The isolated strain harbors 8 virulence genes including Lip, Alt, and Act, with a median lethal dose (LD₅₀) of 1.00×10¹⁰ CFU/mL for M. albus.The isolated strain is highly sensitive to 11 drugs including piperacillin, ceftriaxone, and doxycycline, while carrying 17 resistance genes such as blaTEM, aadA1, and aadA2, thus being identified as a multidrug-resistant strain.Strain Ac240602 exhibits moderate biofilm-forming ability and is an ESBLs (extended-spectrum β-lactamase)-producing positive strain. The carried resistance gene blaTEM shares 100% sequence identity with TEM-1 (GenBank accession no.: MT387455.1) and shows close evolutionary relationship with TEM-155 and TEM-47.The isolated strain is sensitive to traditional Chinese medicines such as Schisandra chinensis, Mume Fructus, and Paeoniae Radix Rubra. This study provides theoretical basis and data support for the infection and comprehensive prevention and control of Aeromonas in M. albus.