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Enterobacter sakazakii is a motile, peritrichous, gram-negative rod that was previously known as a yellow pigmented Enterobacter cloacae. It is documented as a rare cause of outbreaks and sporadic cases of life-threatening neonatal meningitis, necrotizing enterocolitis, and sepsis. E. sakazakii has been isolated from milk powder-based formulas, and there is thus a need to investigate whether and where E. sakazakii occurs in these manufacturing environments. For this purpose, a simple detection method was developed based on two features of E. sakazakii: its yellow pigmented colonies when grown on tryptone soy agar and its constitutive alpha-glucosidase, which is detected in a 4-h colorimetric assay. Using this screening method, E. sakazakii strains were isolated from three individual factories from 18 of 152 environmental samples, such as scrapings from dust, vacuum cleaner bags, and spilled product near equipment. The method is useful for routine screening of environmental samples for the presence of E. sakazakii.

Every year at least 1.5 to 6% of the Dutch population suffers from foodborne illnesses. This may result in symptoms like vomiting or diarrhoea but can in some cases also lead to death. Processes like pasteurisation or sterilisation reduce the number of pathogenic bacteria in food products. Food safety is further controlled by implementing systems like Good Manufacturing Practices (GMP) and Hazard Analysis Critical Control Points (HACCP). Although these preventive measures do improve food safety, the presence of pathogenic bacteria can never be completely eliminated. Therefore, there is always a probability of becoming ill after consuming a food product. This probability can be estimated using Microbiological Risk Asessment (MRA).For one element of MRA, the exposure assessment, the food chain is evaluated from the raw materials to the final product to estimate the level of pathogens in a food product at the moment of consumption. Predictive modelling techniques are combined with process engineering models to evaluate the effect of food processing steps on microbial survival and food safety. The same approach can be used to evaluate processes for other factors than microbiological hazards as was demonstrated in the evaluation of food processing on the accumulation of salts in a potato product. This approach proved to be useful to obtain quantitative information of the process and find critical points in the system.In MRA, usually, only growth or inactivation in the different process steps is considered and re-introduction of bacteria during the production process is not taken into account. However, when pathogens re-enter the product after an inactivation step, this can cause foodborne illness. It is therefore relevant to quantify this recontamination so that it can be incorporated in MRA. A literature review, however, revealed that not many available recontamination models are directly applicable to the food industry.The objective of this thesis was therefore to quan