Summary:
Multidrug-resistant bacterial infections, particularly those caused by Staphylococcus aureus, are recognized
as one of the greatest threats of the 21st century. Bloodstream infections are the most severe staphylococcal
disease manifestation and are often fatal despite our best and most current therapies. Organ abscesses are
primary contributors to S. aureus systemic infections and serve as initial reservoirs for the invading pathogen.
Abscess formation itself follows distinct developmental stages, is actively facilitated by host and bacterium, and
ultimately creates an advantageous niche for S. aureus. While past studies have generated an overview of
abscess architecture, we lack information on the molecular composition of abscesses, particularly in the context
of different abscess stages. This limited knowledge of the molecular events during abscess formation is
especially alarming, for it hinders meaningful attempts at targeted design of anti-staphylococcal strategies.
Our preliminary data show that abscess formation is characterized by the host’s extensive relocation of
transition metals in proximity to the abscess in a process known as nutritional immunity. Consequently, in vivo
imaging reveals that bacteria within the abscess are starved for zinc and iron. Since available metal levels can
serve as biomarkers for invading pathogens, we hypothesize that fluctuating elemental distributions orchestrate
bacterial activities associated with abscess formation. Along these lines, we showed that zinc starvation primes
S. aureus for subsequent contact with different immune cell populations. Beyond these findings, however, the
chronology and factors involved in metal relocation, detection of these stimuli by S. aureus, and corresponding
bacterial responses are entirely unexplored. We thus plan to address these questions in this proposal.
One current barrier to the design of meaningful investigations into the development of staphylococcal tissue
abscesses is a significant degree of abscess heterogeneity, likely a result of different developmental stages of
individual lesions in the same organ. To account for the non-synchronous nature of tissue abscesses, we have
identified a group of potential proteinaceous markers for different abscess stages. These proteins will serve as
molecular clocks so we can follow the progression of individual abscesses through the developmental process.
Based on these markers, we will create in vivo reporters and characterize the molecular inventory of developing
abscesses, focusing on changes in elemental and proteinaceous compositions. Here, we will correlate various
in vivo imaging modalities, including 3D-bioluminiscent imaging, MRI, and imaging mass spectrometry, with
advanced proteomics via micro Liquid Extraction Surface Analysis. Once we have established how the abscess
microenvironment changes during different phases of abscess formation, we will perform transcriptome analysis
of bacterial subpopulations to assess how environmental stimuli affect staphylococcal pathophysiology and, in
turn, abscess development. Combined, the proposed experiments will examine the events at the host-pathogen
interface and pave the way for novel and targeted treatment strategies to combat staphylococcal infections.
