Understanding variation in pathogen virulence is a central goal of evolutionary medicine.  In the shape-shifting bacterial pathogen, Pasteuria ramosa, virulence is thought to be mediated by specific bacterial morphotype(s). Accordingly, variation in the virulence of Pasteuriainfections arises from variation in the absolute/relative abundance of virulence-inducing morphotypes in Pasteuriapopulations. Hitherto, testing this hypothesis has been difficult because a lack of fluorescent markers/constructs has prevented the quantification and isolation of morphotypes. In collaboration with Dr. Nina Wale at Michigan State University, we use the Attune CytPix to overcome these critical barriers to understanding Pasteuria’s virulence, by (a) quantifying the absolute/relative abundance of morphotypes in the population and (b) identifying morphotype-specific autofluorescent signatures to enable cell-sorting.