Environmental factors influencing the inactivation of Cronobacter sakazakii by high hydrostatic pressure

Outbreak History, Biofilm Formation, and Preventive Measures for Control of Cronobacter sakazakii in Infant Formula and Infant Care Settings

Previously known as Enterobacter sakazakii from 1980 to 2007, Cronobacter sakazakii is an opportunistic bacterium that survives and persists in dry and low-moisture environments, such as powdered infant formula. Although C. sakazakii causes disease in all age groups, infections caused by this pathogen are particularly fatal in infants born premature and those younger than two months. The pathogen has been isolated from various environments such as powdered infant formula manufacturing facilities, healthcare settings, and domestic environments, increasing the chance of infection through cross-contamination. The current study discusses the outbreak history of C. sakazakii and the ability of the microorganism to produce biofilms on biotic and abiotic surfaces. The study further discusses the fate of the pathogen in low-moisture environments, articulates preventive measures for healthcare providers and nursing parents, and delineates interventions that could be utilized in infant formula manufacturing to minimize the risk of contamination with Cronobacter sakazakii.

Comparative proteomic analysis of Cronobacter sakazakii by iTRAQ provides insights into response to desiccation

Cronobacter sakazakii is a foodborne pathogen throughout the world and survives extremely desiccation stress. However, the molecular basis involved in desiccation resistance of C. sakazakii is still unknown. In this study, the potential desiccation resistance factors of C. sakazakii ATCC 29544 were determined using iTRAQ-based quantitative proteomic analysis. A total of 2775 proteins were identified by iTRAQ, of which 233 showed a different protein expression between control group and desiccation stress group. Among these 233 proteins identified as desiccation resistance proteins, there were 146 proteins downregulated and 87 proteins upregulated. According to the comprehensive proteome coverage analysis, C. sakazakii increased its resistance to desiccation by reducing the gene involved with unnecessary survival functions such as those used for virulence, adhesion, invasion and flagella assembly, while increasing gene expression of genes used in withstanding osmotic stress such as those genes involved in trehalose and betaine uptake. However, the mechanism involved in amino acid metabolism in an osmotic stress response, including the producing of γ-aminobutyric acid in C. sakazakii is still uncertain. This is the first report to determine the potential desiccation resistant factors of C. sakazakii at the proteomic levels.

Comparative Resistance of Bacterial Foodborne Pathogens to Non-thermal Technologies for Food Preservation

In this paper the resistance of bacterial foodborne pathogens to manosonication (MS), pulsed electric fields (PEFs), high hydrostatic pressure (HHP), and UV-light (UV) is reviewed and compared. The influence of different factors on the resistance of bacterial foodborne pathogens to these technologies is also compared and discussed. Only results obtained under harmonized experimental conditions have been considered. This has allowed us to establish meaningful comparisons and draw significant conclusions. Among the six microorganisms here considered, Staphyloccocus aureus is the most resistant foodborne pathogen to MS and HHP and Listeria monocytogenes to UV. The target microorganism of PEF would change depending on the treatment medium pH. Thus, L. monocytogenes is the most PEF resistant microorganism at neutral pH but Gram-negatives (Escherichia coli, Salmonella spp., Cronobacter sakazakii, Campylobacter jejuni) would display a similar or even higher resistance at acidic pH. It should be noted that, in acidic products, the baroresistance of some E. coli strains would be comparable to that of S. aureus. The factors affecting the resistance of bacterial foodborne pathogens, as well as the magnitude of the effect, varied depending on the technology considered. Inter- and intra-specific differences in microbial resistance to PEF and HHP are much greater than to MS and UV. Similarly, both the pH and aw of the treatment medium highly condition microbial resistance to PEF and HHP but no to MS or UV. Growth phase also drastically affected bacterial HHP resistance. Regarding UV, the optical properties of the medium are, by far, the most influential factor affecting its lethal efficacy. Finally, increasing treatment temperature leads to a significant increase in lethality of the four technologies, what opens the possibility of the development of combined processes including heat. The appearance of sublethally damaged cells following PEF and HHP treatments could also be exploited in order to design combined processes. Further work would be required in order to fully elucidate the mechanisms of action of these technologies and to exhaustively characterize the influence of all the factors acting before, during, and after treatment. This would be very useful in the areas of process optimization and combined process design.

Bacterial maximum non-inhibitory and minimum inhibitory concentrations of different water activity depressing solutes

The NaCl MNICs (maximum non-inhibitory concentrations) and MICs (minimum inhibitory concentrations) for growth of various strains of six bacterial species were determined and then compared with those obtained for seven other solutes. The influence of prior growth conditions on the MNICs and MICs was also evaluated. No significant changes on the MNICs and MICs were found among the strains studied within each species. Among all factors investigated, only growth phase -for Gram-negatives- and growth at high NaCl concentrations led to a change in the NaCl MNICs. Species could be classified depending on its NaCl MNICs and MICs (in decreasing order) as follows: Staphylococcus aureus, Listeria monocytogenes, Cronobacter sakazakii, Enterococcus faecium, Escherichia coli and Salmonella Typhimurium. Similar results were obtained for KCl, LiCl, and sodium acetate, but not for the remaining solutes investigated (sucrose, glycerol, MgCl2 and CaCl2). Results obtained indicate that, in general, Gram-negatives showed lower MNICs and MICs than Gram-positives for all the solutes, S. aureus being the most solute tolerant microorganism. When compared on a molar basis, glycerol showed the highest MNICs and MICs for all the microorganisms -except for S. aureus- and LiCl the lowest ones. NaCl MNICs and MICs were not significantly different from those of KCl when compared on a molar basis. Therefore, the inhibitory action of NaCl could not be linked to the specific action of Na(+). Results also showed that the Na(+) tolerance of some species was Cl(-) dependent whereas for others it was not, and that factors others than aw-decrease contribute to the inhibitory action of LiCl, CaCl2 and MgCl2.