克雷白氏肺炎桿菌 CG43 對多黏菌素的抗性調控分析

Abstract

It has been demonstrated that the seven-gene pmr operon and ugd respectively encode the proteins for the synthesis of 4-aminoarabinose to modify the phosphate residues of lipopolysaccharide (LPS). The decrease of the net negative charge by the LPS modification allows protection of the bacteria from the attack of the cationic antimicrobial peptide polymyxin B. In comparison of the pmr upstream sequences of Klebsiella pneumoniae, Salmonella enterica, Esherichia coli and Yersinia pestis, the putative PhoP and PmrA binding boxes were identified in the counterpart of K. pneumoniae and Y. pestis. Different from Y. pestis, the pmrD homologue was only present in the genome of K. pneumoniae. Deletion of either pmrH, pmrF or ugd reduced the resistance to 2 units/ml polymuxin B. The deletion mutants of phoP, pmrA, or pmrD also appeared to decrease their resistance to polymyxin B. Promoter activity measurement using LacZ as reporter revealed a reduction of PpmrH activity in phoP or pmrA mutant. However, deletion of phoP, pmrA or rcsB had no apparent effect on the expression of Pugd-1 indicating a different regulation of polymyxin B resistance in K. pneumoniae from that in S.enteric. RT-PCR analysis demonstrated that the ugd with the upstream manC and manB are organized as an operon indicating the presence of another promoter of ugd, namely Pugd-2. The activity of Pugd-2 reduced in the rcsB mutant. However, the deletion of rcsB had no apparent effect on the polymyxin B resistance. Finally, deletion of pmrF, phoP or pmrA was found to reduce the bacterial survival in the cells of either THP-1 or RAW264.7.