Transcriptomic Analysis ofSalmonellaDesiccation Resistance

Abstract

The survival of Salmonella in low moisture foods and processing environments remains a great challenge for the food industry and public health. To explore the mechanisms of Salmonella desiccation resistance, we studied the transcriptomic responses in Salmonella Tennessee (Tennessee), using Salmonella Typhimurium LT2 (LT2), a strain weakly resistant to desiccation, as a reference strain. In response to 2 h of air-drying at 11% equilibrated relative humidity, approximately one-fourth of the open reading frames (ORFs) in the Tennessee genome and one-fifth in LT2 were differentially expressed (>2-fold). Among all differentially expressed functional groups (>5-fold) in both strains, the expression fold change associated with fatty acid metabolism was the highest, and constituted 51% and 35% of the total expression fold change in Tennessee and LT2, respectively. Tennessee showed greater changes in expression of genes associated with stress response and envelope modification than LT2, while showing lesser changes in protein biosynthesis expression. Expression of flagella genes was significantly more inhibited in stationary phase cells of Tennessee than LT2 both before and after desiccation. The accumulation of the osmolyte trehalose was significantly induced by desiccation in Tennessee, but no increase was detectable in LT2, which is consistent with the expression patterns of the entire trehalose biosynthesis and degradation pathways in both strains. Results from this study present a global view of the dynamic desiccation responses in Salmonella, which will guide future research efforts to control Salmonella in low moisture environments.

Thermal Resistance and Gene Expression of both Desiccation-Adapted and Rehydrated Salmonella enterica Serovar Typhimurium Cells in Aged Broiler Litter

“…Our finding is consistent with data from some previous studies (12,14,15). These observations may indicate that while the formation of filaments may be critical for long-term persistence in low-a w environments, this may not be the case when bacteria are desiccated under certain conditions, such as in aged broiler litter.…”

“…Another tentative explanation could be attributed to the fact that different strains were used. In support of this notion, Li et al (15) found that trehalose synthesis in S. Tennessee was significantly induced by a 2-h desiccation, while no induction was detected in S. Typhimurium LT2, indicating that there are drastic differences in gene expression patterns under desiccation conditions among different strains.…”

“…ProV, encoded by the proV gene, serves the energy-coupling function in the ProU transport system for glycine betaine in Salmonella (31, 32). Li et al (15) reported that after a 2-h desiccation in a desiccator (a w , 0.11), the proV genes in S. enterica serovar Tennessee and S. Typhimurium LT2 were significantly induced by 12.5-and 14.9-fold, respectively. In a previous study by Finn et al (12), the proV gene was among the most highly upregulated genes following a 4-h desiccation on a stainless steel coupon.…”

“…The change in the fatty acid composition of the cell membrane can affect fluidity and thermodynamics, which is believed to allow the cell to adapt to adverse conditions (39). Li et al (15) reported that the fadA gene was upregulated 94-and 64-fold in S. Tennessee and S. Typhimurium LT2 after desiccation, respectively, which represented the greatest expression change in both strains. When Chen et al (7) studied the expression of fatty acid biosynthesis-associated genes in Salmonella cells desiccated in granulated sugar (a w , 0.80) for 14 days, the fadA gene was observed to be upregulated.…”

“…Desiccation-associated genes were selected based on data reported in the literature (10)(11)(12)(13)(14)(15). Quantitative real-time reverse transcriptase PCR (qRT-PCR) was performed in a Mastercycler ep gradient S thermal cycler (Eppendorf, Hamburg, Germany) using the SuperScript III Platinum SYBR green one-step qRT-PCR kit (Thermo Fisher Scientific Inc.).…”