Stamping Out Staph

Notorious superbug MRSA may have had its media heyday some years ago, but Staphylococcus aureus infections still cause about 20,000 deaths in the US each year. How can we reduce this number? Understanding infection-related abscess formation and host responses is key – so Elizabeth Neumann and colleagues set out to do just that by applying a combination of imaging, MALDI-MS, and codetection by indexing (CODEX) multiplexed immunofluorescence microscopy to tissue samples from infected patients.

“MALDI-MS provides information for hundreds to thousands of discrete molecules within a biological system,” says Elizabeth. “This information is sometimes difficult to relate to known cell types or tissue functional units, complicating data analysis and integration. CODEX immunofluorescence and other multiplexed immunofluorescence microscopy approaches are inherently targeted and allow us to fluorescently stain cell-defining proteins.” Correlating these two techniques is thus useful for connecting the molecular information obtained from MALDI-MS with well-defined tissue structures.

Although it sounds good on paper, data co-registration represents a significant challenge in practice. “We accomplish this by acquiring autofluorescence microscopy on both tissue sections, providing a common imaging modality to facilitate data integration,” says Elizabeth. The natural complexity of host-pathogen interactions also presents complications, as does the need to create and validate antibodies for accurate cell typing. “Because CODEX IF is a fairly new technology, most antibodies of interest must be conjugated and tested in-house rather than being commercially available,” she explains.

Results thus far are promising. Elizabeth’s initial experiments have provided clues as to which immune cells are the first to combat the pathogen, which cells of the kidney are most affected by infection and abscess formation, and how these factors change throughout infection. Interestingly, B cells and macrophages are highly correlated with one another, while progenitor kidney cells are anticorrelated with the presence of staph. We can also visualize differential immune cell responses to different abscesses within the tissue. The next step? Expanding this understanding to the specific biomolecules involved in these changes. As Elizabeth says: “This will help us better understand how S. aureus damages human health – and perhaps how to counteract it.”