| Summary: | 碩士 === 國立中興大學 === 昆蟲學系所 === 96 === Chitin and chitosan were extracted from larvae of Musca domestica and Tenebrio molitor, and dry shrimp (Neocaridina sp.) in this study, the productive rates of chitin were 1.56, 1.72 and 3.59%, respectively, and the productive rates of chitosan were 1.29, 1.46 and 2.29%, respectively. By the solubilities in the acetic acid solution, we could make sure the two extracts were chitin and chitosan. Chitin from three different organic sources had no antibacterial activity, whiles all of chitosan had antibacterial activity. Chitosan expressed a widely spectrum of antibacterial activity against Klebsiella pneumoniae CCRC 10694 and Vibrio parahamelytics CCRC 10806, and also against the strains isolated from clinic, Salmonella cholearasuis, , Streptococcus intermedius, Citrobacter koseri, Staphylococcus xylosus, Streptococcus alactolyticus, hemolytic Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa, confirming that chitosan presents a widely spectrum of antibacterial effect. The minimal inhibitory concentration and minimal bactericidal concentration of three kinds of chitosan against 10 strains of bacteria were in the range of 0.125-0.5%. No significant difference of antibacterial activity among the three chitosan in these tests, and either no significant difference between the antibacterial activity of chitosan against Gram-negative and Gram-positive bacteria. According to the lethal time test, all the Gram-positive bacteria were completed dead below 6 hours, besided S. xylosus, where as over 6 hours, all of Gram-negative bacteria were completely dead. The results of lethal time test showed that there was a significant difference of lethal time between the Gram-negative and Gram-positive bacteria after treating of chitosan. Under existing of 0.5% chitosan, all the median lethal time (LT50) of 10 strains of bacteria were below 2 hours. Under the scanning electron microscope, we observed the surface on E. coli perforated by chitosan, and bacterial were also lysed by chitosan, while no perforation was observed on the surface of S. aureus. The MICs of ampicillin and amoxicillin risen to 32-64 µg/ml from 4-8 µg/ml and 16-32 µg/ml, respectively, suggested that chtiosan and penicillins antibiotics might be antagonistic with each other in application of antibacterial activity.
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