Raman Spectroscopic Characterization of Packaged L. pneumophila Strains Expelled by T. thermophila

The intracellular lifestyle of L. pneumophila within protozoa is considered to be a fundamental process that supports its survival in nature. However, after ingesting the cells of L. pneumophila, some protozoa expel them as compressed live cells in the form of small rounded pellets. The pellets of tightly packaged viable but not culturable forms (VBNCFs) as well as highly infectious mature intracellular forms (MIFs) of L. pneumophila are considered as infectious particles most likely capable to cause human infection. Since L. pneumophila cells are hardly culturable from these pellets, detection methods for packaged live L. pneumophila forms remaining in water should be cultivation free. Hence, we demonstrate the potential of Raman microspectroscopy to directly sort pellets containing L. pneumophila cells, expelled by T. thermophila, and to characterize them on the basis of their Raman spectra.