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.

Quantitative approach to assess the compliance to a performance objective (PO) of Campylobacter jejuni in poultry meat in France.

Predictive modelling is used in microbiological risk assessment to quantify the growth and inactivation of microorganisms through the use of mathematical models. Campylobacter jejuni is one of the main foodborne pathogens and broiler meat is considered as the most important source of human campylobacteriosis. The purpose of this study was to assess the effects of heating and chilling during the poultry slaughter process on inactivation kinetics of Campylobacter jejuni during chilled storage in order to predict its contamination level prior to preparation and consumption in the consumer's home, and then to assess the compliance to a Performance Objective (PO). Three strains of C. jejuni were submitted to consecutive heat (54 °C for 3 min) and cold (3 °C for 2 h) stresses, mimicking the two main slaughtering steps, i.e. scalding and chilling, by inoculating chicken fillets with three different concentrations (4, 6 and 8 log10 CFU/g). Fillets were then stored at 6 °C during 17 days under the modified atmosphere currently used by food processors (70% O2/30% CO2). For all strains, bacterial log reduction was the lowest when inoculated at 8 log10 CFU/g. One strain showed an enhanced resistance during cold storage after application of stressing steps, suggesting an impact of the cell history on further bacterial resistance. Taking strain variability into account, after six days of storage, predictions showed compliance of ready-to-be-cooked chicken meat with a hypothetical PO of 2.55 log10 CFU/g, value set before the meat enters the consumer's home by the ICMSF (International Commission on Microbiological Specifications for Foods). This study opens the path to assess the compliance to a PO of Campylobacter jejuni in poultry meat and more generally provides inputs to refine microbiological risk assessment by taking into account the cell history and more particularly the impact of stressful steps on the subsequent inactivation at consumer's home.

Influence of cell history on the subsequent inactivation of Campylobacter jejuni during cold storage under modified atmosphere.

Worldwide, Campylobacter infections are the main cause of human bacterial enteritis and broiler meat is considered as the most important source of human campylobacteriosis. Some mitigation strategies have been focused on reduction of Campylobacter at the slaughtering steps. This study aimed to determine the influence of consecutive stresses inspired by slaughtering steps on the subsequent inactivation of Campylobacter jejuni during cold storage under different modified atmospheres. Using a full experimental design, three strains of C. jejuni of poultry origin were submitted to consecutive heat (46°, 50° or 54 °C for 4 min) and cold (-4° or 3 °C for 2 h) stresses by plunging cultures into baths at appropriate temperatures. Cultures were then stored at 6 °C during seven days under modified atmospheres (70% O2/30% CO2 or 50% CO2/50% N2). Inactivation of C. jejuni induced by cold storage was shown to depend significantly (P < 0.0001) upon the heat stress previously applied. It was shown to be the highest under the atmosphere enriched in oxygen, after application of 54 °C. Strain inactivation variability was also quantified. These results show that consecutive stresses influence further inactivation of C. jejuni during storage and consequently the contamination level at consumer's plate.

Quantification of Campylobacter jejuni contamination on chicken carcasses in France.

Highly prevalent in poultry, Campylobacter is a foodborne pathogen which remains the primary cause of enteritis in humans. Several studies have determined prevalence and contamination level of this pathogen throughout the food chain. However it is generally performed in a deterministic way without considering heterogeneity of contamination level. The purpose of this study was to quantify, using probabilistic tools, the contamination level of Campylobacter spp. on chicken carcasses after air-chilling step in several slaughterhouses in France. From a dataset (530 data) containing censored data (concentration <10CFU/g), several factors were considered, including the month of sampling, the farming method (standard vs certified) and the sampling area (neck vs leg). All probabilistic analyses were performed in R using fitdistrplus, mc2d and nada packages. The uncertainty (i.e. error) generated by the presence of censored data was small (ca 1 log10) in comparison to the variability (i.e. heterogeneity) of contamination level (3 log10 or more), strengthening the probabilistic analysis and facilitating result interpretation. The sampling period and sampling area (neck/leg) had a significant effect on Campylobacter contamination level. More precisely, two "seasons" were distinguished: one from January to May, another one from June to December. During the June-to-December season, the mean Campylobacter concentration was estimated to 2.6 [2.4; 2.8] log10 (CFU/g) and 1.8 [1.5; 2.0] log10 (CFU/g) for neck and leg, respectively. The probability of having >1000CFU/g (higher limit of European microbial criterion) was estimated to 35.3% and 12.6%, for neck and leg, respectively. In contrast, during January-to-May season, the mean contamination level was estimated to 1.0 [0.6; 1.3] log10 (CFU/g) and 0.6 [0.3; 0.9] log10 (CFU/g) for neck and leg, respectively. The probability of having >1000CFU/g was estimated to 13.5% and 2.0% for neck and leg, respectively. An accurate quantification of contamination level enables industrials to better adapt their processing and hygiene practices. These results will also help in refining exposure assessment models.