Surveillance of listeriosis in Navarre, Spain, 1995-2005--epidemiological patterns and characterisation of clinical and food isolates.

We monitored the incidence of human listeriosis in Navarre, a region in north of Spain between 1995 and 2005, and carried out the characterisation of Listeria monocytogenes isolates obtained from clinical samples and ready-to-eat products (sliced cooked meat, smoked salmon and liver pate). The active surveillance requesting hospitals to notify all listeriosis cases (n=40) yielded higher incidence rates (average annual rate 0.65/100,000 inhabitants, range 0.18-1.18/100,000 inhabitants) than expected. Pregnant women were the largest group affected (n=13, 32.5% of the cases), with a peak in incidence during the last three years of the study period. From the 40 human cases we obtained 33 Listeria isolates. Serological and molecular characterisation by PFGE identified 20 different pulsotypes, which on three occasions enabled us to link sporadic cases into clusters. Although we could not identify the incriminated food product we found two clinical pulsotypes among smoked salmon and cooked meat isolates. Surveillance of listeriosis in Spain should be improved and coordinated with other European Union Member States in order to better estimate the burden of disease and to prevent foodborne outbreaks.

Characterization of Listeria monocytogenes and Listeria innocua from a vegetable processing plant by RAPD and REA.

The incidence of Listeria monocytogenes in a vegetable processing plant was investigated over a 23-month period. Frozen ready-to-eat vegetable samples, well as the plant environment, were sampled. The molecular subtyping techniques, Random Amplified Polymorphic DNA (RAPD) and Restriction Endonuclease Analyses (REA), were performed to help investigate the origin and routes of Listeria dissemination. The low and sporadic incidence of L. monocytogenes made it impossible to establish an epidemiological sequence in the processing plant, though a case of cross-contamination between tomato and ratatouille was detected. Listeria innocua subtyping, however, allowed us to determine the prevalence of several strains in vegetables, and their presence on machinery samples suggested the possibility of cross-contamination during processing. The low incidence of L. monocytogenes indicated that the risk of listeriosis transmission by vegetable consumption is low. On the other hand, the isolation of the same strain of L. innocua in several surveys pointed out the risk of colonisation on surfaces and machinery. The persistence of Listeria spp. is a cause for concern as can lead to future contamination of vegetables processed in the plant and to a possible increased risk for health. Therefore, periodic controls for the presence of Listeria spp. and a further review of the cleaning and disinfection procedures used in frozen vegetable plants are recommended.

Random amplified polymorphic DNA typing applied to the study of cross-contamination by Listeria monocytogenes in processed food products.

The presence of Listeria spp. was investigated in 369 samples of cooked meat products and 52 of smoked salmon. Incidences of 17.6% for cooked meat and 38.5% for smoked salmon samples were found. All Listeria monocytogenes isolates (34 from meat products and 16 from smoked salmon) were typed serologically and by random amplified polymorphic DNA (RAPD) typing using primers HLWL74 (5'-ACGTATCTGC-3'), HLWL85 (5'-ACAACTGCTC-3'), and OMP-01 (5'-GTI'GGTGGCT-3'). Strains from cooked meat products were characterized and compared in relation to their origin. The detection of identical strains in products of different type and brand packed on the same date suggested cross-contamination, probably during the slicing process. All L monocytogenes isolates from smoked salmon were indistinguishable by serotyping and RAPD, suggesting that this strain was highly disseminated and adapted to the treatment used for the preservation of this food. RAPD subtypes were analyzed using GelCompar version 4.1 software and the unweighted pair method using arithmetic averages, and six groups with at least 78% similarity were established. Serotyping and RAPD results were in concordance, although RAPD showed a higher discriminatory power with L. monocytogenes isolates from meat products. RAPD is an easy method that could be useful to detect cross-contamination occurring during postprocessing manipulations.

Partial replacement of sodium chloride with potassium chloride in dry fermented sausages: Influence on carbohydrate fermentation and the nitrosation process.

Two types of dry fermented sausages were manufactured: type A with traditional formulation and type B with reduced sodium content. pH and a(w) values and the counts of aerobic mesophiles, Enterobacteriaceae and lactobacilli micro-organisms during the ripening of both fermented sausages were similar. Final lactic acid contents were also similar, but carbohydrate content was significantly lower in type B sausage. Content of acetic, propionic and butyric acids were significantly higher in type B, suggesting a higher heterofermentative activity. Also type B sausage showed lower nitrate level and higher chemical conversion percentage, suggesting a higher nitrosation intensity.