Shigella sonnei Does Not Use Amoebae as Protective Hosts.

and bacteria cause the majority of all shigellosis cases worldwide. However, their distributions differ, with predominating in middle- and high-income countries and predominating in low-income countries. One proposed explanation for the continued range expansion of is that it can survive in amoebae, which could provide a protective environment for the bacteria. In this study, we demonstrate that while both and can survive coculture with the free-living amoebae , bacterial growth is predominantly extracellular. All isolates of were degraded following phagocytosis by , unlike those of , which can replicate intracellularly. Our data suggest that is not able to use amoebae as a protective host to enhance environmental survival. Therefore, alternative explanations for emergence need to be considered. The distribution of species closely mirrors a country's socioeconomic conditions. With the transition of many populous nations from low- to middle-income countries, infections have emerged as a major public health issue. Understanding why infections are resistant to improvements in living conditions is key to developing methods to reduce exposure to this pathogen. We show that free-living amoebae are not likely to be environmental hosts of , as all strains tested were phagocytosed and degraded by amoebae. Therefore, alternative scenarios are required to explain the emergence and persistence of infections.