The roles of UDP-glucose dehydrogenase in polymyxin B susceptibility, swarming and virulence factor expression in Proteus mirabilis.
Date Issued
2009
Date
2009
Author(s)
Lin, Tzu-Yi
Abstract
Proteus mirabilis is a facultative Gram-negative bacterium and a member of the family Enterobacteriaceae. It’s a normal flora in intestines of healthy human. However, it’s an opportunistic pathogen in immunodificent patients who use urethral catheters in long-term therapy. It frequently causes urinary tract infection (UTI), even kidney disease, pneumonia and septicemia.olymyxin B is a kind of cationic antimicrobial peptides. While the positive-charge structure of polymyxin B combine with the negative-charge bacterium membrane, the bacterium membrane is disrupted by fatty-acid chains of polymyxin B and leak the cytoplasm contents out. It is known that the modification of the lipid A of the lipopolysaccharides (LPSs) in Gram-negative bacteria by 4-amino-4-deoxy-L-arabinose (L-Ara4N) decreases negative charge of the membrane. In this way, polymyxin B couldn’t bind the membrane, then leading to the resistance of polymyxin B. . mirabilis is naturally resistant to polymyxin B, but the underlying mechanism of drug resistance is not known clearly. By mini-Tn5 transposon mutagenesis, we selected a mutant that was susceptible to polymyxin B. The Tn5-inserted site was ugd gene that was predicted to encode the UDP-glucose dehydrogenase in P. mirabilis. ugd gene is associated with polysaccharides and L-Ara4N synthesis in Escherichia coli and Salmonella Typhimurium. The ugd mutant exhibited reduced swarming ability, decreased flagellin synthesis, decreased number of swarmer cells, decreased haemolysin activity, decreased cell invasion ability, and alterations of LPS and membrane integrity. Complementation of ugd gene by pACYC-184 vector restored all virulence factor expression in the ugd mutant.e used real time RT-PCR to investigate the mechanism of nonswarming of the ugd mutant. We found the reduced mRNA expression of umoA、B、D membrane proteins which could up-regulate the flhDC operon, and flhDC, fliA and flaA which are class I, II and III genes of flagellar synthesis in the ugd mutant. This implies that ugd gene mutation will affect the expression of umoA、B、D proteins and then decrease the expression of downstream flhDC, fliA and flaA. In addition, reporter assay indicated ugd gene mutation led to increased expression of rpoE. It implies ugd mutation could create a stress condition and can be sensed by RpoE. It has been shown that RppA/RppB, a two-component system, is associated with polymyxin B resistance in P. mirabilis. By real-time RT-PCR and reporter assay, we investigate if ugd gene is under the control of RppA/RppB. The data indicated that RppA regulated ugd gene expression in the presence of polymyxin B.n this study, we investigated the roles of ugd gene in polymyxin B resistance, swarming ability and virulence factor expression in P. mirabilis.
Subjects
Proteus mirabilis
polymyxin B
UDP-glucose dehydrogenase
SDGs
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