Amino acid substitution at K42 of ribosomal protein S12 play roles in both antimicrobial resistance and virulence in Klebsiella pneumoniae

• Main Authors: Feng Yi-Jhen, 馮翌榛
• Other Authors: Siu Leung-Kei
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/12182882042802564601

碩士 === 國防醫學院 === 微生物及免疫學研究所 === 101 === Streptomycin was introduced as a therapeutic agent in early 1940s and its resistance could be arised by a mutation in the rpsL gene, which encodes the ribosomal protein S12. The mutations at K42 of S12 protein have often been found to confer a high-level streptomycin resistance. However, no study has been made on the contribution of varied types of amino acid substitution at K42 of S12 protein in antimicrobial resistance and virulence. In this study, I have tried to construct all the mutants of 19 kinds of K42 substitution by using site-directed mutagenesis and gene replacement in Klebsiella pneumoniae. Eleven mutants of different K42 substitution have been constructed successfully and high-level streptomycin resistance was found in all these mutants. Virulence of these mutants was further evaluated by growth rate, serum resistance, neutrophils phagocytosis, and mouse lethality assays. In comparing to the parental strain, the K42R mutant showed non-observable affects on these assays, and K42C mutant exhibited a lower growth rate; the other nine K42 mutants presented a reduction of growth rate and became susceptible to normal human serum. In the mice LD50 (the bacterial dose that caused 50% death) assay, except K42R mutant, all the other ten K42 mutants were at least ten-fold less lethal (>2×103 cfu) than the parental strain (~2×102 cfu). In conclusion, the streptomycin resistance caused by K42 substitution of S12 protein is often associated with reduction of virulence in K. pneumoniae.