Multiple imaging methods probe host-pathogen interactions

Abscesses associated with bacterial infections are a complex mixture of host cells and bacteria. And not all the bacteria behave the same way even within a single abscess. Because such lesions are so heterogeneous, much remains unknown about the interactions between host cells and pathogens. To get a better picture of what’s going on, Eric P. Skaar and coworkers at Vanderbilt University combined multiple imaging methods to observe the competition for metals between Staphylococcus aureus and an infected mouse (Sci. Transl. Med. 2018, DOI: 10.1126/scitranslmed.aan6361). They used magnetic resonance imaging to line up images obtained by other methods. By using laser ablation inductively coupled plasma mass spectrometry, they were able to determine the distribution of various metal nutrients. The images revealed that abscesses are rich in calcium and relatively deprived of manganese, iron, and zinc. Within a single lesion, some bacteria can be nutrient rich while others are nutrient starved. The researchers used MALDI mass spectrometry imaging to map mouse and bacterial proteins involved in the stress response to infection. By lining up both types of mass spec images, the researchers were able to identify proteins that are spatially associated with metal distribution. The imaging methods could lead to culture- and label-free methods of pathogen diagnosis, the researchers note.