Understanding Metabolic Activity During the Inoculum Effect
Abstract
With the post antibiotic era upon us, new techniques are required to treat bacterial infections. While the mechanisms of acquired resistance to antibiotics are well studied, mechanisms by which bacteria can resist antibiotics in the absence of acquired resistance are less studied. This is called phenotypic resistance. One form of phenotypic resistance is the inoculum effect (IE) where the initial density of a bacterial population determines the minimum inhibitory concentration (MIC) of an antibiotic. Given recent findings showing that the metabolic rate of bacteria determines its susceptibility to antibiotics, we sought to understand how changes to metabolism and growth determined IE. We grew Escherichia coli in different metabolites and quantities of casamino acids, which allowed for a variety of metabolic and growth rates to be tested. We then quantified the difference in MIC between high density and low-density populations. Interestingly, we found that one nucleotide metabolite, uracil, was able to reduce the difference in MIC between both populations to zero, effectively removing IE. Alternatively, growth in the nucleotide adenine increases the inoculum effect. Interestingly, our study has shown that uracil increases the production of adenine to maintain an equal AT/GC ratio. This, in turn, and increases metabolic rate via increased flux through nucleotide synthesis pathways. Overall, our work suggests a unique role of nucleotide synthesis in potentiating IE. Our results may reduce the concentration of antibiotics required to eliminate an infection and may lead to the identification of novel druggable targets.
Faculty Sponsors
Dr. Robert Smith, Dr. Allison Lopatkin
Project Type
Event
Location
Alvin Sherman Library
Start Date
4-6-2021 12:00 PM
End Date
4-9-2021 12:00 PM
Understanding Metabolic Activity During the Inoculum Effect
Alvin Sherman Library
With the post antibiotic era upon us, new techniques are required to treat bacterial infections. While the mechanisms of acquired resistance to antibiotics are well studied, mechanisms by which bacteria can resist antibiotics in the absence of acquired resistance are less studied. This is called phenotypic resistance. One form of phenotypic resistance is the inoculum effect (IE) where the initial density of a bacterial population determines the minimum inhibitory concentration (MIC) of an antibiotic. Given recent findings showing that the metabolic rate of bacteria determines its susceptibility to antibiotics, we sought to understand how changes to metabolism and growth determined IE. We grew Escherichia coli in different metabolites and quantities of casamino acids, which allowed for a variety of metabolic and growth rates to be tested. We then quantified the difference in MIC between high density and low-density populations. Interestingly, we found that one nucleotide metabolite, uracil, was able to reduce the difference in MIC between both populations to zero, effectively removing IE. Alternatively, growth in the nucleotide adenine increases the inoculum effect. Interestingly, our study has shown that uracil increases the production of adenine to maintain an equal AT/GC ratio. This, in turn, and increases metabolic rate via increased flux through nucleotide synthesis pathways. Overall, our work suggests a unique role of nucleotide synthesis in potentiating IE. Our results may reduce the concentration of antibiotics required to eliminate an infection and may lead to the identification of novel druggable targets.
