Analysis of the survival capacity and transcriptional response of Salmonella enterica serovar infantis under stress conditions of clinical and food safety relevance

Aims Analyze the survival and transcriptional response of Salmonella Infantis (S. Infantis) against acid, oxidative, increased osmolarity, and thermal stresses. Methods and Results 25 strains isolated from human, food and veterinary sources in Brazil between 2013–2018 were analyzed. 8 log10 CFU·mL⁻¹ inoculums were exposed for 10 min, 1 h or 24 h to: acid stress (HCl pH 2.6); oxidative stress (15 mmol·L⁻¹ H2O2); NaCl 9%; refrigeration (4°C); freezing (-20°C); and heating (63/74°C). Most strains (n = 22) survived the acid stress after 10 min and 1 h. Strains maintained high populations under oxidative stress (>87.7%) and NaCl 9% (111.4%). No strains survived heating, while refrigeration prevented multiplication (approximately 101%), and freezing reduced populations (<92.6%). Strain 1143/14 had its transcriptome sequenced under acid and oxidative stresses, and NaCl 9%. 14 up-regulated and 38 down-regulated transcripts under acid stress, and 407 up-regulated and 143 down-regulated under oxidative stress were expressed, associated to biological processes of response and adaptation. No transcripts were differentially expressed with NaCl 9%. Conclusions S. Infantis survival against most stresses represents a challenge for its control. The efficacy of heating reinforced its importance to control Salmonella in food. While acid survival involved the expression of virulence and broad stress response genes, oxidative stress survival showed the expression of genes specific to the adaptation to this condition.