| Summary: | 碩士 === 長庚大學 === 生物醫學研究所 === 101 === Streptococcus parasanguinis is one of the primary colonizers of the tooth surface and a frequent isolate of the dental plaque. The incidence of S. parasanguinis FW213 in endocarditis is well documented. Three putative collagen binding proteins, Spaf_0420, Spaf_1570, and Spaf_1574, are identified from the genome of S. parasanguinis FW213 recently. In this study, the functions of these loci were investigated. The result of substrate analysis indicated that all three ORFs were able to bind to multiple extracellular matrix molecules. The overall biofilm formation of Spaf_1574-deficient mutant (ΔSpaf_1574) was similar to that of the wild-type FW213. Inactivation of Spaf_0420 (ΔSpaf_0420) reduced the biofilm formation by 28%, whereas the Spaf_1570-deficient strain (ΔSpaf_1570) exhibited 42% increase in biofilm formation compared to FW213 under the same growth condition. Comparing with the wild-type FW213, the biofilm generated by ΔSpaf_0420 in a flow-cell system was without any complicated structures, whereas the biofilm of ΔSpaf_1570 was with a tight structure. All three mutant strains exhibited a reduced colonization efficiency to trypsin-treated swine heart valves. Furthermore, the toxicity of strains ΔSpaf_0420 and ΔSpaf_1570 was lower than that of FW213 in the Galleria mellonella model, suggesting that both ORFs are critical for the survival of S. parasanguinis against host immune clearance. Taken together, the collagen-binding protein homologues are important for the optimal pathogenic capacity of S. parasanguinis FW213.
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