Biomarkers are characteristic molecular or cellular events that are measurable indicators of normal or abnormal processes linking environmental inputs to phenotypic outputs. Biomarkers are ubiquitously used to diagnose and treat complex human diseases such as cancer and cardiovascular disease, and are also used to identify the presence of infectious agents. Such indices enhance the ability of clinicians to manage their patients.
Theoretically, biomarkers can be established for pathogenetic bacteria that report on antibiotic susceptibility, provided these are measurable and quantifiable biological parameters. We have previously investigated the detectability of cell death phenotypes in an E. coli model using methods commonly used to assess apoptosis in eukaryotic cells. These results serve as a starting point for defining and characterizing the distribution of "abnormal" values among bacterial species.
Hoechst labeling of compacted DNA in antibiotic-treated E. coli
Annexin V labeling of phosphatidylserine on antibiotic-treated E. coli
Our research interests lie in defining and characterizing "abnormal" biomarker levels in pathogens identified in the CDC's 2013 Threat Report. We are taking three approaches to address the question of whether antibiotic susceptibility biomarkers can be established: 1) We are generating reference limits to arrive at arbitrary cutoffs that are chosen to define "abnormal" phenotypes. 2) We are generating discrimination limits by evaluating the extent of phenotypic overlap between control and test populations. 3) We are generating threshold limits that identify phenotype intensity values beyond which antibiotic susceptibility decreases.
To accomplish this we are utilizing a diverse variety of biochemical, cell and molecular biology methods along with microscopy and flow cytometry techniques.