Evaluation of tumor-colonizing Salmonella strains using the chick chorioallantoic membrane model

The chick embryo chorioallantoic membrane (CAM) tumor model is a valuable preclinical model for studying the tumor-colonizing process of Salmonella enterica serovar Typhimurium. It offers advantages such as cost-effectiveness, rapid turnaround, reduced engraftment issues, and ease of observation. In this study, we explored and validated the applicability of the partially immune-deficient CAM tumor model. Herein, we demonstrate that Salmonella preferentially colonizes tumors and directly causes tumor cell death. Bacterial migration, tumor colonization, and intra-tumor distribution did not require flagellar-mediated motility. The vast majority of Salmonella that colonized the CAM tumor were extracellular. Thus, tumor invasion was independent of both Salmonella pathogenicity island-1-encoded and Salmonella pathogenicity island-2-encoded type III secretion systems. Surprisingly, the extracellular residence of Salmonella on CAM tumors did not require biofilm formation. We evaluated our wild-type parental strain compared to the attenuated clinical strain VNP20009 and discovered a reduced tumor colonization capability of VNP20009. The inability to effectively colonize CAM tumors potentially explains the reduced anti-tumor efficacy of VNP20009. Our work establishes the xenograft CAM model as an informative and predictive screening platform for studying tumor-colonizing Salmonella.