Risk Assessment or Assessment of Risk? Developing an Evidence-Based Approach for Primary Producers of Leafy Vegetables To Assess and Manage Microbial Risks.

Over the last 10 years, some high-profile foodborne illness outbreaks have been linked to the consumption of leafy greens. Growers are required to complete microbiological risk assessments (RAs) for the production of leafy crops supplied either to retail or for further processing. These RAs are based primarily on qualitative judgements of hazard and risks at various stages in the production process but lack many of the steps defined for quantitative microbiological RAs by the Codex Alimentarius Commission. This article is based on the discussions of an industry expert group and proposes a grower RA approach based on a structured qualitative assessment, which requires all decisions to be based on evidence and a framework for describing the decision process that can be challenged and defended within the supply chain. In addition, this article highlights the need for evidence to be more easily available and accessible to primary producers and identifies the need to develop hygiene criteria to aid validation of proposed interventions.

Glycine betaine transport by Staphylococcus aureus: evidence for feedback regulation of the activity of the two transport systems.

The regulation of glycine betaine accumulation by Staphylococcus aureus was investigated. The accumulation of glycine betaine was regulated by the osmotic pressure of the medium and the low affinity transport system played the major role in this regulation. Mutants were isolated that lack the low affinity, osmotically activated glycine betaine/proline transport system. Such mutants accumulated glycine betaine via the high affinity system but the glycine betaine pool was smaller and responded poorly to osmotic pressure changes. The regulation of glycine betaine transport has revealed that at the steady state net influx is reduced and that this is achieved by inhibition of both the low affinity and the high affinity transport systems. Cells pre-loaded with glycine betaine exhibited a reduced Vmax for both systems: the low affinity system was reduced in activity fivefold and the high affinity system was reduced 10-fold and became virtually undetectable. Although glycine betaine transport at the steady state is reduced, retention of the compatible solute is an active process since addition of an uncoupler provokes rapid release of the accumulated material. These data suggest that feedback regulation of the activity of the uptake systems is a major mechanism for controlling the level of compatible solute accumulation.

Glycine betaine transport by Staphylococcus aureus: evidence for two transport systems and for their possible roles in osmoregulation.

The transport of glycine betaine by Staphylococcus aureus was investigated. Two transport systems were found that could be differentiated on the basis of their affinity for glycine betaine and their activation by osmotic pressure. The high-affinity system was relatively independent of osmotic pressure and exhibited a Km of approximately 3 microM. This system was not inhibited by proline, for which a separate high-affinity transport system has been recently discovered. The low-affinity system was activated approximately 35-fold by an increase in osmotic pressure and exhibited a Km of approximately 130 microM for glycine betaine. This system is partially inhibited by excess proline and may be identical to the low-affinity system recently described for proline. Both glycine betaine transport systems are Na(+)-dependent.