Phenotypic analyses of Salmonella enterica serovar Enteritidis strains isolated in the pre- and post-epidemic period in Brazil

Salmonella Enteritidis has caused, since the 1980s, a sustained epidemic of human infections in many countries. This study analyzed S. Enteritidis strains isolated before and after the epidemic period in Brazil regarding their capacities to survive to acid, oxidative, and high-temperature stresses, and capacity to grow in egg albumen. Moreover, the ability to invade human epithelial cells (Caco-2) and to survive inside human (U937) and chicken (HD11) macrophages was checked. Post-epidemic strains showed a better ability to survive after 10 min under acid stress at 37 °C (P ≤ 0.05). However, both groups of strains showed similar ability to survive after 1 h under acid stress at 37 °C and at 42 °C independently of the time of exposure. Similar ability was verified in both groups of strains regarding oxidative stress, growth in egg albumen, high-temperature stress, invasion to Caco-2 cells, and invasion and survival in macrophages. In conclusion, post-epidemic S. Enteritidis strains showed a better ability to survive under the acid stress found in the stomach, which might be an advantage to reach the intestine and colonize chickens and humans. However, both groups of strains did not differ significantly in the majority of the phenotypic tests analyzed in this study.