Stress resistance of emerging poultry-associated Salmonella serovars

In recent years, the on-farm prevalence of some poultry-related Salmonella serovars such as S. Kentucky, S. Heidelberg, S. Livingstone and S. Mbandaka has increased significantly, even replacing S. Enteritidis and S. Typhimurium as the most frequently isolated serovars in some production settings and countries. For this reason, the aim of this work was to determine the resistance to several stressing agents and food preservation technologies, in laboratory media and in egg products, of 4 strains of these emerging Salmonella serovars associated to poultry and poultry products and to make comparisons with 4 S. Enteritidis strains. First, the resistance to acid pH, hydrogen peroxide, NaCl, heat, HHP, PEF and UV of the 8 Salmonella strains studied was determined and compared in laboratory media. From this part of the study, it was concluded that variability in resistance to stress among the 8 studied strains varied depending on the investigated agent/technology. However, differences in resistance (2D-values) were always lower than 3.3-fold. Results obtained also indicated that the strains of the emerging serovars studied would display lower acid and NaCl resistance, higher heat resistance and similar oxidative, HHP, PEF and UV resistance than S. Enteritidis. Then, the resistance of these 8 strains was evaluated and compared in egg, egg products and poultry manure. For some agents -including osmotic stresses, UV and PEF- there was a very good correspondence between the results obtained in laboratory media and in real food matrices and poultry manure (r > 0.85; p < 0.01). A significant relationship was also found for acid and HHP resistance (p < 0.05) and a trend for heat resistance (p < 0.10). Therefore, in general terms, conclusions drawn from the study carried out in laboratory media - regarding intraspecific variability and the relative resistance of the different strains - might be extrapolated, although with caution, to real food scenarios. Results obtained in this investigation would help to better understand the physiology and ecology of Salmonella and to design better egg preservation strategies.