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 and 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 (∼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 with biological processes of response and adaptation. No transcripts were differentially expressed with NaCl 9%.

Conclusions: Salmonella 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.