SPEG and infection: Finally, to verify whether the lack of the speG gene confers a selective advantage during infection in EIEC, we performed an in vitro competitive assay analyzing the survival within macrophages of strain HN280 transformed with a plasmid harbouring/lacking a functional copy of speG. To this end, HN280 pULS13 and HN280 pACYC184 were grown to OD600 0.6–0.7, mixed and used to infect a murine macrophage cell line (J774).