Trustworthy Identification of Resistance Biomarkers of Bacillus weihenstephanensis: Workflow of the Quality Assurance Procedure

Quantification of Campylobacter jejuni gene expression after successive stresses mimicking poultry slaughtering steps

Broiler meat is considered as the most important source of the foodborne pathogen Campylobacter jejuni. Exposure to stress conditions encountered during the slaughtering process may induce bacterial adaptation mechanisms, and enhance or decrease pathogen resistance to subsequent stress. This adaptation may result from changes in bacterial gene expression. This study aims to accurately quantify the expression of selected C. jejuni genes after stresses inspired from the poultry slaughtering process. RT-qPCR was used to quantify gene expression of 44 genes in three strains after successive heat and cold stresses. Main results indicated that 26 genes out of 44 were differentially expressed following the successive thermal stresses. Three clusters of genes were differentially expressed according to the strain and the stress condition. Up-regulated genes mainly included genes involved in the heat shock response, whereas down-regulated genes belonged to metabolic pathways (such as lipid, amino-acid metabolisms). However, four genes were similarly overexpressed in the three strains; they might represent indicators of the thermal stress response at the species scale. Advances in the molecular understanding of the stress response of pathogenic bacteria, such as Campylobacter, in real-life processing conditions will make it possible to identify technological levers and better mitigate the microbial risk.

Bacillus cereus cshA Is Expressed during the Lag Phase of Growth and Serves as a Potential Marker of Early Adaptation to Low Temperature and pH

The spore-forming bacterium B. cereus is a major cause of foodborne outbreaks in Europe. Some B. cereus strains can grow at low temperatures and low pH in many processed foods. Modeling of the bacterial lag time is hampered by a lack of knowledge of the timing of events occurring during this phase. In this context, the identification of lag phase markers, not currently available, could be a real advance for the better prediction of lag time duration. Currently, no molecular markers of this phase are available. By determining that cshA was always expressed early during the lag phase, we provide a molecular marker of the early adaptation process of B. cereus cells when exposed to low temperature and pH.

Bacterial adaptation is characterized by a lag phase during which cells do not multiply or modify their physiology to cope with the constraints of their environment. Our aim was to determine a sequence of events during the lag phase of growth at low temperature and pH for three Bacillus cereus strains. The onsets of expression of two genes, one of which is essential for stress adaptation (cshA, coding for a RNA helicase) and one of which is involved in the transition between lag phase and exponential phase (abrB, coding for a transition regulator), were determined using fluorescent transcriptional reporter systems. Regardless of the stressing conditions and the tested strains, the cshA promoter was active very early, while the biomass increased and always did so before the first cell division. At 12°C and pH 7.0, the onset of cshA promoter activity occurred at between 3 h and 7 h, while the bacterial counts started to increase at between 12 h and 13 h. At pH 5.0 and at 20°C or 30°C, the onset of cshA promoter activity occurred before 1 h and earlier than at pH 7.0. In contrast, the onset of abrB promoter activity depended on the strain and the stressing conditions. In the ATCC 14579 strain, the onset of abrB promoter activity always started at between 30 min and 3 h, before biomass increased and cell division occurred. For the other strains, it took place along with the first cell division at 12°C but did so much later during growth under the other tested conditions.

IMPORTANCE The spore-forming bacterium B. cereus is a major cause of foodborne outbreaks in Europe. Some B. cereus strains can grow at low temperatures and low pH in many processed foods. Modeling of the bacterial lag time is hampered by a lack of knowledge of the timing of events occurring during this phase. In this context, the identification of lag phase markers, not currently available, could be a real advance for the better prediction of lag time duration. Currently, no molecular markers of this phase are available. By determining that cshA was always expressed early during the lag phase, we provide a molecular marker of the early adaptation process of B. cereus cells when exposed to low temperature and pH.