Date of Completion
TWO COMPONENT SYSTEM, ANTIBIOTIC RESISTANCE
Field of Study
Doctor of Philosophy
In this study, we report two previously unidentified mechanisms that governs β-lactam
and antimicrobial peptide resistance.
In Gram-negative bacteria, production of β-lactamases is often induced in response to
the antibiotic- associated damage to the cell wall. Here, we have identified a previously
unidentified mechanism that governs β-lactamase production. In the Gram-negative
enteric pathogen Vibrio parahaemolyticus, we found a histidine kinase/response
regulator pair (VbrK/VbrR) that controls expression of a β-lactamase. Mutants lacking
either VbrK or VbrR do not produce the β-lactamase and are no longer resistant to β-
lactam antibiotics. Notably, VbrK autophosphorylation is activated by β-lactam
antibiotics, but not by other lactams. However, single amino acid substitutions in the
putative periplasmic binding pocket of VbrK leads its phosphorylation in response to
both β-lactam and other lactams, suggesting that this kinase is a β-lactam receptor that
can directly detect β-lactam antibiotics instead of detecting the damage to cell wall
resulting from β-lactams. In strong support of this idea, we found that purified
periplasmic sensor domain of VbrK binds penicillin, and that such binding is critical for
VbrK autophosphorylation and β lactamase production. Direct recognition of β-lactam
antibiotics by a histidine kinase receptor may represent an evolutionarily favorable
mechanism to defend against β-lactam antibiotics.
Antimicrobial peptide is amphipathic peptide that inserts into phospholipid bilayer and
disrupt the integrity of bacterial cell membrane. Many bacteria employ the strategy of
LPS modification to resist attack from AMPs. Here, we have identified a mechanism that
governs LPS modification that has never been reported in Vibrio parahaemolyticus
before. We identified a histidine kinase/response regulator pair (PvrK/PvrR) that
controls expression a lipid A ethanolamine phosphotransferase (PEA transferase), an
enzyme adds positively charged phosphoethanolamine (PEA) to the core of lipid A.
Resistance to AMPs or the expression of PEA transferase drastically decrease in
mutants lacking either PvrK or PvrR. The autophosphorylation of PvrK can be
stimulated through either low Mg2+ concentration or the presence of AMPs, which
resembles the host environment when Vibrio parahaemolyticus invades the host.
Li, Lu, "Antibiotic Resistance Regulated by Two-Component Regulatory System in Vibrio parahaemolyticus" (2018). Doctoral Dissertations. 1736.
Available for download on Saturday, April 11, 2020