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

Identification and Disruption of the proBA Locus in Listeria monocytogenes: Role of Proline Biosynthesis in Salt Tolerance and Murine Infection

Intracellular accumulation of the amino acid proline has previously been linked to the salt tolerance and virulence potential of a number of bacteria. Taking advantage of the proBA mutant Escherichia coli CSH26, we identified a listerial proBA operon coding for enzymes functionally similar to the glutamyl kinase (GK) and glutamylphosphate reductase (GPR) enzyme complex which catalyzes the first and second steps of proline biosynthesis in E. coli. The first gene of the operon, proB, is predicted to encode GK, a 276-residue protein with a calculated molecular mass of 30.03 kDa and pl of 5.2. Distal to the promoter and overlapping the 3′ end of proB by 17 bp is proA, which encodes GPR, a 415-residue protein with a calculated molecular mass of 45.50 kDa (pl 5.3). Using this information, we created a chromosomal deletion mutant by allelic exchange which is auxotrophic for proline. This mutant was used to assess the contribution of proline anabolism to osmotolerance and virulence. While inactivation of proBA had no significant effect on virulence in mouse assays (either perorally or intraperitoneally), growth at low (2 to 4% NaCl) and high (>6% NaCl) salt concentrations in complex media was significantly reduced in the absence of efficient proline synthesis. We conclude that while proline biosynthesis plays little, if any, role in the intracellular life cycle and infectious nature of Listeria monocytogenes, it can play an important role in survival in osmolyte-depleted environments of elevated osmolarity