Abstract: AIMS: To investigate the main effects and interactions of different factors : divercin V41 (0-4 ng ml(-1)), NaCl content (0.5-5.5% w v(-1)), phenol (liquid smoke) concentration (0-8 ppm), and pH (5.5-7.5) on Listeria monocytogenes ScottA growth. METHODS AND RESULTS: Experiments were carried out in BHI broth using a central composite design. Divercin V41 (div41), NaCl content and pH were found to be the most influential factors whereas phenol concentration in liquid smoke had no effect on L. monocytogenes ScottA growth in our experimental domain. The combined effects of div41, NaCl content and pH decreased L. monocytogenes ScottA maximum specific growth rate (mu(max)) from 0.34 to 0.01 h(-1) and led to a significant increase in lag time (t(lag)) from 5.5 to 25 h. CONCLUSION: In this study, NaCl, pH and phenol conditions were similar to those currently observed in smoked salmon production. This shows that L. monocytogenes ScottA growth could be efficiently delayed by the use of div41 in addition to the usual technological hurdles. SIGNIFICANCE AND IMPACT OF THE STUDY: In conclusion, the technological hurdles of cold smoked salmon production could be further optimized and combined with the use of div41 or the div41 producer strain to improve the food safety of the product.

Abstract: A complete factorial design 2(3) was used to study some aspects of Carnobacterium divergens V41 metabolism (growth, biogenic amine production, and divercin V41 production) in sterile cold-smoked salmon extract (SSE) at varying temperatures (3 to 9 degrees C), NaCl levels (2.5 to 6.5%), and glucose concentrations (2 to 6 g liter(-1)). The results showed that temperature and NaCl content were the most influential factors on growth parameters in SSE. Predictive models are suggested for the assessment of C. divergens lag time (t(lag)) and maximum specific growth rate (micro(max)) Among the biogenic amines studied, only tyramine was found to be produced by C. divergens in SSE. Furthermore, we showed that temperature, NaCl, and glucose variations did not greatly affect tyramine and divercin V41 production by the bacteria under the experimental conditions used. Indeed, divercin V41, a bacteriocin from C. divergens V41 that is highly active against some Listeria strains, was produced in SSE even under harsh culture conditions. Similarly, tyramine production in SSE was delayed at 3 degrees C but reached 35 microg ml(-1) in all experiments after 27 days of storage. However, this final tyramine concentration in SSE is low compared with the threshold values of 100 to 800 microg g(-1) reported as the potentially toxic dose in foods. Thus, we have found that C. divergens V41 is a promising strain for the biopreservation of refrigerated cold-smoked salmon.

Abstract: AIMS: The objective of this study was to determine the technological behaviour (implantation and biogenic amines production) of Carnobacterium divergens V41, an anti-Listeria bacteriocin producer (divercin V41), after inoculation in cold smoked salmon (CSS). METHODS AND RESULTS: Implantation of the strain was followed by multiplex-PCR during 27 days of storage at 4 degrees C, and biogenic amines were quantified by HPLC. It was found that the strain was able to develop quite well in CSS among lactic wild flora. Divercin V41 (400 AU ml-1) was produced in CSS, and the biogenic amine content was not modified by inoculation of the bacteria. CONCLUSIONS: Carnobacterium divergens V41 is a safe, interesting, bioprotective agent. SIGNIFICANCE AND IMPACT OF THE STUDY: This strain could potentially be used for efficient prevention of L. monocytogenes growth in CSS.

Abstract: Screening of a library of Enterococcus faecalis insertional mutants allowed isolation of a mutant affected in tyramine production. The growth of this mutant was similar to that of the wild-type E. faecalis JH2-2 strain in Maijala broth, whereas high-performance liquid chromatography analyses showed that tyramine production, which reached 1,000 microg ml(-1) for the wild-type strain, was completely abolished. Genetic analysis of the insertion locus revealed a gene encoding a decarboxylase with similarity to eukaryotic tyrosine decarboxylases. Sequence analysis revealed a pyridoxal phosphate binding site, indicating that this enzyme belongs to the family of amino acid decarboxylases using this cofactor. Reverse transcription-PCR analyses demonstrated that the gene (tdc) encoding the putative tyrosine decarboxylase of E. faecalis JH2-2 is cotranscribed with the downstream gene encoding a putative tyrosine-tyramine antiporter and with the upstream tyrosyl-tRNA synthetase gene. This study is the first description of a tyrosine decarboxylase gene in prokaryotes.

Abstract: The specific detection and enumeration of Lactobacillus brevis LB62, Carnobacterium divergens V14 and Carnobacterium piscicola VI were studied by in situ hybridization-flow cytometry. The method was performed on the exponential growth phase with three probes targeting 16S rRNA labelled with fluorescein isothicyanate (FITC): EUB338 probe universal for Eubacteria, Lb probe specific for Lact. brevis and Cb probe specific for the genus Carnobacterium. EUB338 was used to determine the permeabilization and hybridization conditions for the cells. The Lb probe gave no hybridization signal whereas the Cb probe allowed the detection and quantification by flow cytometry at 520 nm of the two Carnobacterium strains in pure culture or in mixtures with Listeria innocua F.