Caco-2 Invasion by Cronobacter sakazakii and Salmonella enterica Exposed to Drying and Heat Treatments in Dried State in Milk Powder

Abstract

Due to the ability of foodborne pathogens to survive in low moisture food, the decontamination of milk powder is an important issue in food protection. The safety of food products is, however, not always insured and the different steps in the processing of food involve physiological and metabolic changes in bacteria. Among these changes, virulence properties may also be affected. In this study, the effect of drying and successive thermal treatments on the invasion capacity of Salmonella Typhimurium, Salmonella Senftenberg, and Cronobacter sakazakii was assessed. Bacteria were dried on milk powder at three different water activity levels (0.25, 0.58, and 0.80) and heated at two different temperatures (90°C and 100°C) for 30 and 120 s. After recovery, stressed bacterial populations were placed in contact with Caco-2 cells to estimate their invasion capacity. Our results show that drying increases the invasion capacity of foodborne pathogens, but that heat treatment in the dried state did not exert a selective pressure on bacterial cells depending on their invasion capacity after drying. Taken together, our findings add to the sum of knowledge on food safety in dried food products and provide insight into the effects of food processing.

Uncovering the Mechanisms of Halotolerance in the Extremely Acidophilic Members of the Acidihalobacter Genus Through Comparative Genome Analysis

“…The Kdp system was shown to play a role in increasing the osmotolerance of Escherichia coli , Staphylococcus aureus and Sinorhizobium meliloti by allowing scavenging of K + when concentrations are low (Laimins et al, 1981; Gowrishankar, 1985; Domínguez-Ferreras et al, 2009; Price-Whelan et al, 2013). The genes kdpA , kdpB , and kdpC were found to be upregulated by 27-, 15-, and 8-fold, respectively, in Cronobacter sakazakii under osmotic stress (Lang et al, 2017). It is possible that the presence of this system in A. prosperus DSM 14174 renders this strain more resilient to salt stress than the other members of the genus when inhabiting K + limited environments.…”

Impact of the Resistance Responses to Stress Conditions Encountered in Food and Food Processing Environments on the Virulence and Growth Fitness of Non-Typhoidal Salmonellae

“…Typhimurium and S . Senftenberg cells [ 116 ], and the study by Yoon et al, (2013), who observed that exposure of S . Enteritidis cells to NaCl increased their cell invasion efficiency (Table 1) [ 117 ].…”

“…The same authors reported that upon that heat shock the genes of two Salmonella pathogenicity islands (SPI-2 and SPI-5) were upregulated, which would explain their higher adhesion and would confer a higher chance of survival in the host while genes of SPI-1 were downregulated. In another study, Lang et al, 2017 compared the invasion ability of dried Salmonella cells after different heat treatments and likewise did not find any differences with the non-heat treated cells, although, in this case, the reduced metabolic activity of dried cells might explain the absence of effects of the heat treatment [ 116 ]. To the best of our knowledge there is only one work in which the virulence of stable variants/clones of Salmonella cells has been examined and the results of this work indicated that the heat resistant strain displayed a lower pathogenicity after intraperitoneal injections into 20–22 g mice [ 229 ].…”

Quantitative Detection of Viable but Nonculturable Cronobacter sakazakii Using Photosensitive Nucleic Acid Dye PMA Combined with Isothermal Amplification LAMP in Raw Milk

“…Most cases of C. sakazakii infection can be traced back to powdered infant formula (PIF), which often acts as the main source of infection [ 5 ]. Pasteurization, oligonutrition, low temperatures, or drying during the production and processing of PIF may induce C. sakazakii to enter a sublethal state, wherein it remains viable but cannot be cultured on a plate (VBNC) [ 6 , 7 , 8 ].…”