• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.4
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• pp.317-327
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• 1987

As a series of studies on the suitability as a second intermediate host of Clonorchis sinensis, artificial infection experiments were applied to Tilapia mossambica. And then, in order to elucidate the defence mechanism of the fish to Clonorchis, clonorchicidal substance in the epidermal mucus of the fish was isolated by silica gel column and thin layer chromatography and analyzed for its chemical structure by UV, IR and NMR-spectroscopy. The results obtained are summarized as follows: 1. The cercariae which attempted to contact with the fish in the water were observed under stereomicroscope. After contact, the cercariae began to separate their tail from the body after several minutes and then the number increased to $80\%$ more than 10 minutes after the encounter. But very few cercariae could actually invade the epidermis of the fish. 2. The fish were reared with Parafossarulus manchouricus which were shedding numerous cercariae of Clonorchis in the aquarium for 24 hours. Only a few cercariae could invade the epidermis but most of the invaded cercariae died out before forming their cysts. Very few number of the remaining encysted cercariae were also found to be in a state of suspended animation within 42 hours. 3. In the cases of the control fish, Pseudorasbora parva, numerous cercariae of Clonorchis were found to invade the fish through the epidermis under stereomicroscope. Then many metacercariae of Clonorchis were also found in the fish while they were kept in the aquarium. 4. A sample of the epidermal mucus of Tilapia mossambica was extracted with ethly ether 6 times repeatedly. In silica gel column chromatography, using petroleum ether: chloroform/30:70(v/v) as a first solvent and MeOH as a second solvent, the extract was fractionated into the yellow and brownish red solutions in the first solvent and the clonorchicidal brownish yellow solution in the second sovent. 5. The clonorchicidal brownish yellow solution was added to petroleum ether, and the mixture was stored for 5 days at $5^{\circ}C$ and was, then, separated into supernatant fraction and precipitate. Ten mg/ml of the supernatant fraction killed, in vitro, the excysted metacercariae in 45 minutes but the precipitate in 600 minutes. 6. In silica gel column chromatography, using acetone: benzene/10:90(v/v) as a solvent, the more clonorchicidal supernatant fraction was fractionated into the first fraction with Rf. 0.2966 and the second fraction with Rf. 0.072. In vitro, 10mg/ml of the first fraction killed the excysted metacercariae in 28 minutes, the second fraction in 80 minutes and the first fraction was, therefore, determined to be a final clonorchicidal substance. 7. By this purification procedures, the most clonorchicidal substance from the epidermal mucus of Tilapia mossambica was purified 71-folds with $0.2075\%$ yield. Infra red, nuclear magnetic resonance and ultraviolet spectrometric analysis of the purified substance revealed that the substance is linoleic acid. According to the results of the present studies it seemed that this species can not serve as a proper intermediate host of Clonorchis sinensis, and that defence mechanism to the fluke seems to be correlated with linoleic acid in the epidermal mucus of this species.

• Journal of Food Hygiene and Safety
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• v.39 no.1
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• pp.54-60
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• 2024

This study investigated the effectiveness of using pathogens and aqueous acids to reduce the Aspergillus ochraceus and Rhodotorula mucilaginosa contamination in livestock production environments. For this study, 1 mL of each bacterial suspension (10⁷-10⁸ spores/mL) was inoculated on a knife surface, dried at 37℃, and used under each treatment condition. First, to investigate the effect of organic acids, acetic, lactic, and citric acids were used. Subsequently, to select the appropriate concentration, they were prepared at concentrations of 0.5, 1, 2, 3, 4, and 5%, respectively. Accordingly, to further maximize the effect of organic acid treatment, we combined the treatment with ultraviolet light. The two strains showed a significant difference (P<0.05) compared to the initial strain, with a greater than 90% decrease in the concentrations of all organic acids. Consequently, acetic and lactic acids decreased by approximately 5 and 2 log colony forming unit (CFU)/cm², respectively, when treated with ultraviolet light (360 mJ/cm²); however, citric acid decreased by less than 1 log CFU/cm². However, when manufactured with 4% acetic acid, a severe malodor was emitted, making it difficult for workers to use it in a production environment. Accordingly, the optimal treatment conditions for organic acid and ultraviolet light for application were selected as follows: immersion in a 4% lactic acid solution for 1 minute and then, sterilization with ultraviolet light at 360 mJ/cm². Finally, when a pork meat sample was cut with a knife that was finally washed with lactic acid and treated with ultraviolet light, the low level of inoculum transferred from the cleaned knife to the surface of the sample was not detected. In conclusion, using this established method can prevent cross-contamination of the surface of the meat during processing.