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| Isolation, Identification and Pathological Analysis of Aeromonas caviae from Micropterus salmoides |
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| DOI：10.16768/j.issn.1004-874X.2024.07.007 |
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| Abstract: |
| 【Objective】 The study was conducted to investigate the causes of sudden death of largemouth bass
(Micropterus salmoides) in a bass culture base in Shenzhen-Shanwei Special Cooperation Zone, and reveal the biological
characteristics of the Pathogen, with an aim to provide theoretical reference for disease prevention, treatment and prevention
in breeding largemouth bass.【Method】 A dominant bacterial strain, named SZNH-S20230817, was isolated from the
liver, spleen, intestine and lesion tissues of the diseased largemouth bass, and the isolate was subsequently subjected to
morphological characteristics observation, physiological and biochemical characteristics identification, artificial infection
experiment, drug sensitivity test, MIC and MBC determination, 16S rRNA sequencing, identification of resistance genes and
virulence genes to analyse its drug resistance and pathology. 【Result】 The results showed that the extended 16S rRNA
sequence of SZNH-S20230817 had a 99.38% homology with Aeromonas caviae AP019195, and also carried four virulence
genes, including aer, act, lip and fl a. The results of physiological and biochemical identification showed that, indole, oxidase,
phenylalanine, mannitol, xylose, arginine dihydrolysate and glucose acid production of the strain were positive, and the strain
SZNH-S20230817 was identified as Aeromonas caviae. Regression infection revealed that the strain SZNH-S20230817
was highly pathogenic, with an LC50 of 1.39×107
CFU/mL for largemouth bass. The results of drug sensitivity tests showed
that the bacterium was resistant to 12 antibiotics such as cefazolin, kanamycin, tetracycline and vancomycin, ampicillin, and
clindamycin, and also carried 13 resistance genes such as qnrS, catI, emrB, Sul1, rmtB and etc. Histopathological analysis
showed that infection with the strain SZNH-S20230817 could cause swelling and freeing of splenocytes, fracture and rupture
of intestinal mucosa, shedding of villi, necrosis of renal cells, infiltration of inflammatory cells and vacuolisation of hepatic cells
in the fish. The results of in vitro bacterial inhibition tests showed that the bacterium had low MIC and MBC against rheum
officinale and gallnut, and the remaining seven herbs had weak inhibition against the bacterium.【Conclusion】 Aeromonas
caviae is the pathogen that causes the sudden death of largemouth bass, which carries four virulence genes of aer, act, lip and
fl a, and has an LC50 of 1.39×107
CFU/mL against largemouth bass. It is resistant to antibiotics such as cefazolin, kanamycin and
tetracycline. Low dose of rheum officinale and gallnut can inhibit the growth of the bacterium effectively, with good preventive
and inhibitory effects. |
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