The main theme of my work is to analyze phenotypic heterogeneity in bacterial cells and explore how this phenotypic heterogeneity impacts our health. Reversible drug tolerant phenotypes are thought to underlie the propensity of recurrent infections to relapse, and little is known about the physiology of these rare and transient sub- populations. Deeper understanding of the molecular make-up of these cell types will facilitate the development of therapeutics. Therefore, a major goal of my research is to study their physiology: the metabolite, RNA, protein, and regulatory content that allow them to tolerate extraordinary concentrations of drugs.
1. Knowledge of bacterial persister physiology remains scarce due to the difficulties associated with segregation of these rare and transient cells from other cell-types. Given these technical limitations, FACS in conjunction with antibiotic tolerance assays has become a highly useful method to quantify persister physiology. Using this approach, we are able to characterize the persister physiology of E. coli at different growth stages and under different growth conditions.
a) Orman MA, Brynildsen MP. Dormancy is not necessary or sufficient for bacterial persistence, Antimicrobial Agents and Chemotherapy, 2013, 57(7): 3230-3239.
b) Orman MA, Henry TC, DeCoste CJ, Brynildsen MP, Analyzing persister physiology with fluorescence activated cell sorting, Methods in Molecular Biology, 2016, 1333: 83-100.
c) Orman MA, Brynildsen MP, Inhibition of Stationary Phase Respiration Impairs Persister Formation in coli, Nature Communications, 2015, 6:7983.
d) Amato S, Orman MA, Brynildsen MP. Metabolic Control of Persister Formation in Escherichia coli, Molecular Cell, 2013, 5(4):475-487.
2. Even though bacterial persistence has been mostly studied genetically, its metabolic capabilities have been ignored by the persister research community. Persistence can be thought of as a metabolic program, and our contribution to this area is significant. I developed a method to measure persister metabolic activities that leverages the phenomenon of metabolite-enabled aminoglycoside potentiation in persisters. This technique can be used to study persister metabolism in heterogeneous populations, thereby circumventing the current technical challenges associated with isolating high purity persister samples. Performing this assay allows measurement of nutrient catabolism to drive respiratory activity in persisters, which generates knowledge of the metabolic pathways that can be targeted to devise novel anti-persister strategies.
a) Orman MA, Brynildsen MP. Establishment of a method to rapidly assay bacterial persister metabolism, Antimicrobial Agents and Chemotherapy, 2013, 57(9):4398-4409.
b) Orman MA, Mok WWK, Brynildsen MP, Aminoglycoside-enabled Elucidation of Bacterial Persister Metabolism, Current Protocols in Microbiology, 2015, 36:17.9.1-17.9.14.
c) Mok WWK*, Orman MA*, Brynildsen MP, Impacts of Global Regulators on Persistence Metabolism, Antimicrobial Agents and Chemotherapy, 2015, 59(5):2713-2719. *Contributed equally
3. Burns cause a large portion of accidental deaths each year in the United States, and the danger posed by burns is not always obvious. Microbes can enter through the burn site, but additional hazards are present within the victim’s own body. Pathogens from the gastrointestinal tract cause some of the most serious burn complications, likely due to the disruptions in the mucosal barrier. The activation of the host immune system by burn injuries and infections causes complex changes in the physiological balance of the body, which can progress to multiple organ dysfunction syndromes with a mortality rate as high as 90-100%. My research in this area aimed at addressing two questions: (i) what are the cellular and molecular signatures of prolonged inflammation caused by burn and septic shocks? And (ii) what are the putative targets that can be used to modulate inflammation?
a) Orman MA, Ierapetritou MG, Androulakis IP, Berthiaume F. Liver Metabolic Response to Experimental Burn Injury Associated with Fasting. PLoS ONE, 2013, 8(2): e54825.
b) Yang Q, Mattick J, Orman MA, Nyugen TT, Ierapetritou MG, Berthiaume F, Androulakis IP. Dynamics of Hepatic Gene Expression Profile in a Rat Cecal Ligation and Puncture Model. Journal of Surgical Research, 2012, 176:583-600.
c) Orman MA, Nyugen TT, Ierapetritou MG, Berthiaume F, Androulakis IP. Comparison of the Cytokine and Chemokine Dynamics of the Early Inflammatory Response in Models of Burn Injury and Infection, Cytokine. 2011, 55:362-371.
d) Orman MA, Berthiaume F, Androulakis IP, Ierapetritou MG. Pathway analysis of liver metabolism under stressed condition. Journal of Theoretical Biology. 2011, 272:131-140.