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Streptococcus iniae is a zoonotic pathogen, which seriously threatens aquaculture and human health worldwide. Antibiotics are the preferred way to treat S. iniae infection. However, the unreasonable use of antibiotics leads to the enhancement of bacterial resistance, which is not conducive to the prevention and treatment of this disease. Therefore, it is urgent to find new efficient and environmentally friendly antibacterial agents to replace traditional antibiotics. In this study, the antibacterial activity and potential mechanism of thymol against S. iniae were evaluated by electron microscopy, lactate dehydrogenase, DNA and protein leakage and transcriptomic analysis. Thymol exhibited potent antibacterial activity against S. iniae in vitro, and the MIC and MBC were 128 and 256μg/mL, respectively. SEM and TEM images showed that the cell membrane and cell wall were damaged, and the cells were abnormally enlarged and divided. 2MIC thymol disrupted the integrity of cell walls and membranes, resulting in the release of intracellular macromolecules including nucleotides, proteins and inorganic ions. The results of transcriptomic analysis indicated that thymol interfered with energy metabolism and membrane transport, affected DNA replication, repair and transcription in S. iniae. In vivo studies showed that thymol had a protective effect on experimental S. iniae infection in channel catfish. It could reduce the cumulative mortality of channel catfish and the number of S. iniae colonization in tissues, and increase the activities of non-specific immune enzymes in serum, including catalase, superoxide dismutase, lysozyme and acid phosphatase. Taken together, these findings suggested that thymol may be a candidate plant agent to replace traditional antibiotics for the prevention and treatment of S. iniae infection.

Gut health is essential for animal growth because it can absorb nutrients more efficiently, promote growth, and protect the body from invasion by pathogenic microorganisms. Temperature, dissolved oxygen, water quality, nutrition level, pathogen, net fishing, and so on will affect the gut health of aquatic animals. Intestinal diseases in aquatic animals were often not easily detected, making them difficult to prevent and control. Therefore, establishing a stable and scientific evaluation standard of gut health was of great significance. This study evaluated the effects of gross pathological and histological parameters of largemouth bass and channel catfish infected by Aeromonas hydrophila. A total of 150 largemouth bass and 150 channel catfish were randomly divided into 5 groups: 1 control group (NC) and 4 challenge groups (CH, fish were infected with A. hydrophila by intraperitoneal injection with a concentration of 200 µL 1x108 CFU/mL, 1x107 CFU/mL, 1x106 CFU/mL, and 1x105 CFU/mL, respectively). After the challenge, largemouth bass' gross pathological and histological changes were observed on the 2nd, 6th, 9th, 12th, and 14th days. In contrast, channel catfish's gross pathological and histological changes were observed on the 3rd, 6th, 9th, 12th, and 15th day. In this study, regarding the "I See Inside" (ISI) methodology of poultry, a pathological evaluation method of fish intestinal health was established to comprehensively evaluate the intestinal health status of fish by gross pathological and histopathological score. In gross pathology, it was scored by the body surface and intestinal lesions. In histology, it was a metric evaluation of histological alterations in the intestine, converting macroscopic and microscopic alterations into numbers and then scoring. Each evaluation parameter sets up an "influence factor" (IF) according to the degree of influence of its pathological changes on intestinal function. The final score was the sum of the IF product and this parameter's score. The results of two kinds of fish showed that the gross pathological and histopathological scores correlated with the infection dose and time. And the significant difference in the score between the enteritis and control groups was observed. The results showed that the higher score, the more serious the pathological changes of fish infected by A. hydrophlia. From this, it can be concluded that the pathological evaluation method established can be used to evaluate the gut health of fish. [ABSTRACT FROM AUTHOR]

The harsh environmental loads may lead to strength failure in the turbine in an aero-engine. To accurately assess the strength reliability of the turbine under multiple loads, the stress distributions of 41 danger sites of a turbine under thermal, centrifugal, and pneumatic loads were determined by the flow-thermal-solid coupling analysis using ANSYS. Second, based on the flow-thermal-solid coupling analysis and response surface method, the probabilistic analysis model of stress at the danger site was established. And the probabilistic distribution of stress was determined by sampling and hypothesis testing. Finally, the reliability model of the turbine with multi-site damage and failure dependency was established, by which a reliability of 0.99802 was calculated. And the actual reliability of the turbine was 0.99626 determined by the Monte Carlo simulations, which verified the model in precision. The results indicated that the reliability model has a high efficiency and higher precision than the traditional reliability model with failure independence. [ABSTRACT FROM AUTHOR]