Desiccation resistance of a large set of Salmonella enterica strains and survival on dry- and wet-inoculated soybean meal through storage

Salmonella enterica Senftenberg (IOC 2319) and Salmonella enterica Typhimurium (ATCC 14028) under low water activity stress: Effects on culturability and cell viability

Salmonella enterica is one of the most important foodborne pathogens for public health worldwide. When Salmonella enterica is exposed to low water activity, changes in cellular behavior may occur. These changes can impact the cells that form a colony on specific nutrient media (culturability) and the metabolically or physiologically active cells (viability) of Salmonella cells, with consequences for the analytical methods and food safety management. Thus, this study studied the impact of continuous and recurrent exposure of S. Senftenberg IOC 2319 and S. Typhimurium ATCC 14028 to water activity (aw) treatments between 0.4 and 0.99 over 24 h and five days. The culturability was determined using the plate count technique, and cell viability was measured by flow cytometry. S. Senftenberg IOC 2319 was shown to be more resistant to aw stress than S. Typhimurium ATCC 14028. A total of 6.9 and 8.5 log CFU/mL reductions were observed for S. Senftenberg IOC 2319 and S. Typhimurium ATCC 14028. Although both bacteria lost culturability on plate counting, the flow cytometry results demonstrated that they remained viable between 7.09 and 9.23 log CFU/mL for S. Senftenberg IOC 2319 and S. Typhimurium ATCC 14028, respectively. This result opens questions about whether they can recover and adapt a food matrix, causing a greater risk to the consumer. In conclusion, low water activity stresses can cause significant changes in Salmonella strains, and the use of Flow cytometry can be a valuable technique to understand the physiological status of microorganisms better and suggest the importance of safer and faster methods for standard microbiological evaluation.

Assessing dry inoculation carriers and Salmonella transfer in low moisture foods: a peanut-based model investigation

Salmonella has been responsible for several foodborne outbreaks associated to low moisture foods (LMFs) worldwide, including peanut based products. In this study the performance of calcium carbonate (aw 0.331), non-fat milk powder (aw 0.226), soil (aw 0.388), crushed peanut skin (aw 0.357) and crushed peanut shell (aw 0.341) as dry carriers for Salmonella was evaluated. In addition, Salmonella dry transfer from soil and crushed peanut skin to peanut kernels was assessed. Immediately after the dry inoculation, the highest Salmonella count was obtained in calcium carbonate, ca. 7 log CFU/g, followed by soil and peanut shells, both with 6.4 log CFU/g, powdered milk, with 6.2 log CFU/g and peanut skin, with 6.0 log CFU/g. However, there was no significant difference (p > 0.05) among the carriers. The stability of Salmonella on the carriers was also evaluated for 7 days at 37 ºC. At the end of the storage time, only peanut skin showed a significant decline in the inoculum load (p < 0.05), with reduction of 2.7 log CFU/g. For the other carriers the Salmonella counts varied by up to 1.2 log CFU/g. Moreover, the Salmonella transfer rate from soil and crushed peanut skin to peanut kernels was 0.14% and 0.10%, corresponding to ca. 4 log CFU/g. After 30 days at 25 ºC, reductions of 2 log CFU/g in the peanut samples were observed. Neither the carriers nor the culture media used to recover the inoculum from peanuts had significant effect on the results (p > 0.05). In conclusion, four out of the five carriers displayed good performance. The indirect inoculation method optimized in this study reduced the inoculum preparation time. In addition, soil and crushed peanut skin showed potential for dry transfer of Salmonella to peanuts, illustrating a representative scenario of cross-contamination of peanuts.

Investigating desiccation resistance, post-rehydration growth, and heat tolerance in desiccation-injured cells of Salmonella enterica isolated from the soybean production chain

This study compared the resistance to different desiccation conditions of 190 Salmonella enterica strains previously isolated from the soybean meal production chain and belonging to 23 serovars. Additionally, the post-rehydration growth and heat tolerance of the strains previously exposed to desiccation were determined. Variability in desiccation resistance was observed both within and between serovars. Strains belonging to S. Havana and S. Schwarzengrund serovars were the most resistant, regardless of storage condition. The drying temperature (20 °C and 30 °C) did not influence the desiccation resistance of the Salmonella strains. On the other hand, increasing drying time from 1 to 7 days reduced Salmonella counts. The origin (isolation sources) also influenced the desiccation resistance of the Salmonella strains. The growth of the Salmonella strains after rehydration varied considerably depending on the drying conditions and incubation temperature during cultivation. An increase in the time and temperature of drying led to a reduction in population of most Salmonella strains after rehydration. Salmonella strains previously desiccated also showed differences in the heat tolerance in all temperature-time binomials tested. Some strains were highly resistant to heat tolerance conditions, presenting <1 log CFU/mL reduction from the initial population. The results obtained in this study suggest that the strategies to mitigate Salmonella in low-aw foods must consider the existence of high-stress resistant strains and their multiple-stress adaptability profiles, including effects of processing, food composition, and storage conditions.

Salmonella enterica Outbreaks Linked to the Consumption of Tahini and Tahini-Based Products

Salmonella is a leading cause of bacterial foodborne illness in the world. Although typically associated with foods of animal origin, low-moisture foods, such as tahini, are quickly gaining recognition as an important vehicle of Salmonella exposure. This review offers the Canadian perspective on the issue of Salmonella in tahini and tahini-based products. A summary of several recent food product recalls and foodborne outbreaks related to the presence of Salmonella in tahini and tahini-based products such as halva are presented. The properties of the food vehicles, their production practices, and potential routes of contamination are discussed. Particular focus is placed on the ecology of Salmonella in the tahini production continuum, including its survival characteristics and response to intervention technologies.

The Quality of Eggs Derived from Japanese Quail Fed with the Fermented and Non-Fermented Rapeseed Meal

The most popular protein source in poultry feed mixtures is soybean. However, cheaper and more available alternative protein sources are being sought, and feed manufacturers more and more often turn their attention to the post-extraction meals of local oil plants, e.g., rapeseed. Therefore, the effect of fermented and non-fermented post-extraction rapeseed meal used as a feed additive for Japanese quails was investigated on the eggs’ quality. The study was performed on 280 females of Japanese quails fed with a mixture without rapeseed meal, with non-fermented post-extraction rapeseed meal (5%, 10% and 15%) and with fermented one (5%, 10% and 15%). During the experiment, eggs were collected from each group four times (every 4 weeks) and evaluated for their quality characteristics. The addition of 10% fermented rapeseed meal had the most beneficial effect on such eggs quality traits as egg weight, specific gravity, yolk index and color and albumen pH. However, in the majority of examined parameters, no significant differences were found between birds fed with soybean meal and those fed with fermented and non-fermented rapeseed meal (morphological elements proportions, yolk weight, albumen height and Haugh’s units, eggshell quality). This supports the thesis that the use of rapeseed meals instead of soybean meals may allow obtaining the proper quality of animal raw materials at a lower cost and with the use of local feed resources.

Salmonella enterica in soybean production chain: Occurrence, characterization, and survival during soybean storage

This study aimed to determine Salmonella enterica occurrence along the soybean meal production chain (raw material, in-processing samples, final products, and in the environment of five processing plants), characterize the isolates, and assess the survival of Salmonella Senftenberg 775W in soybeans stored under different temperature conditions. Among 713 samples analyzed, 12.9% (n = 92) were positive for Salmonella enterica. Dust collected inside and outside processing plants (n = 148) comprised the samples with the highest positivity for Salmonella enterica, 47.3%. The occurrence of Salmonella enterica varied among the different processing plants. Twenty-nine (n = 29) Salmonella serotypes were isolated, with S. Mbandaka as the most frequent serotype, whereas S. Typhimurium was mainly linked to final product samples (soybean meal). S. Senftenberg 775W did not survive for a long time in soybean stored at 20-37 °C, but at 20 °C, cells were viable for more than 60 days. This study suggests that soybean meal may harbor Salmonella serotypes related to foodborne disease outbreaks in humans and can be responsible for Salmonella introduction into livestock and, consequently, in foods of animal origin. This study provides crucial data on contamination pathways of Salmonella in the soybean production chain, contributing to the understanding of Salmonella epidemiology which is strategic for the development of preventive and control measures to reduce the burden of salmonellosis linked to products of animal origin.