Prevalence, characteristics, and selection of Bacillus cereus sub-groups from dairy products for challenge testing and predictive model development.

Prevalence, toxin gene profiles, lactose fermentation, and growth responses of B. cereus sensu lato sub-groups in various dairy and dairy alternative products and ingredients were studied to identify relevant isolates for challenge testing and model development to predict and manage growth responses. Out of 71 examined products or ingredients, 51 B. cereus s.l. isolates were obtained from 35 positive samples (49% prevalence). These 51 isolates along with 18 additional dairy isolates and 12 B. cereus s.l. reference strains were identified using MALDI-TOF. The 81 isolates were further characterized by panC sequencing, testing for cold shock and toxin genes (cspA; hbl, nhe, CytK and ces), lactose fermentation, and study of growth rates (µmax) under various conditions (45°C, 10°C, 6% NaCl, pH 5.1), resulting in 298 µmax-values. These conditions were selected to differentiate mesophilic and psychrotolerant strains and to identify tolerant isolates. Dairy powders (83%), pasteurized upconcentrated cheese whey (43%), and cheeses (42%) had the highest prevalences of B. cereus s.l. and the highest concentrations in positive samples (5-100 CFU/g or ml). The panC groups II, III, IV, VI, and VIII were detected among the dairy isolates, with 97% harbouring one or more toxin genes. Lactose fermentation was observed in 42% of isolates, with lactose-fermenting B. cereus s.l. isolates of panC groups III and IV dominant in dairy powders. Growth rates of B. cereus s.l. varied considerably, among and within panC groups of the dairy isolates. Based on the highest growth rates at 45°C, 10°C, 6 % NaCl, pH 5.1, panC group membership, toxin genes profiles, and lactose fermentation ability, two cocktails of "mesophilic" or "psychrotolerant" isolates were selected. These strain cocktails can be used in future challenge testing and predictive food microbiology studies to evaluate and manage growth of B. cereus s.l. in dairy products and ingredients.

Processing environment monitoring in low moisture food production facilities: Are we looking for the right microorganisms?

Processing environment monitoring is gaining increasing importance in the context of food safety management plans/HACCP programs, since past outbreaks have shown the relevance of the environment as contamination pathway, therefore requiring to ensure the safety of products. However, there are still many open questions and a lack of clarity on how to set up a meaningful program, which would provide early warnings of potential product contamination. Therefore, the current paper aims to summarize and evaluate existing scientific information on outbreaks, relevant pathogens in low moisture foods, and knowledge on indicators, including their contribution to a "clean" environment capable of limiting the spread of pathogens in dry production environments. This paper also outlines the essential elements of a processing environment monitoring program thereby supporting the design and implementation of better programs focusing on the relevant microorganisms. This guidance document is intended to help industry and regulators focus and set up targeted processing environment monitoring programs depending on their purpose, and therefore provide the essential elements needed to improve food safety.

Minimal inhibitory concentrations of undissociated lactic, acetic, citric and propionic acid for Listeria monocytogenes under conditions relevant to cheese.

Minimal inhibitory concentrations (MICs) of undissociated lactic acid were determined for six different Listeria monocytogenes strains at 30 °C and in a pH range of 4.2-5.8. Small increments in pH and acid concentrations were used to accurately establish the growth/no growth limits of L. monocytogenes for these acids. The MICs of undissociated lactic acid in the pH range of 5.2-5.8 were generally higher than at pH 4.6 for the different L. monocytogenes strains. The average MIC of undissociated lactic acid was 5.0 (SD 1.5) mM in the pH range 5.2-5.6, which is relevant to Gouda cheese. Significant differences in MICs of undissociated lactic acid were found between strains of L. monocytogenes at a given pH, with a maximum observed level of 9.0 mM. Variations in MICs were mostly due to strain variation. In the pH range 5.2-5.6, the MICs of undissociated lactic acid were not significantly different at 12 °C and 30 °C. The average MICs of undissociated acetic acid, citric acid, and propionic acid were 19.0 (SD 6.5) mM, 3.8 (SD 0.9) mM, and 11.0 (SD 6.3) mM, respectively, for the six L. monocytogenes strains tested in the pH range 5.2-5.6. Variations in MICs of these organic acids for L. monocytogenes were also mostly due to strain variation. The generated data contribute to improved predictions of growth/no growth of L. monocytogenes in cheese and other foods containing these organic acids.