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This study describes the genetic analysis of the riboflavin (vitamin B 2 ) biosynthetic (rib) operon in the lactic acid bacterium Lactococcus lactis subsp. cremoris strain NZ9000. Functional analysis of the genes of the L. lactis rib operon was performed by using complementation studies, as well as by deletion analysis. In addition, gene-specific genetic engineering was used to examine which genes of the rib operon need to be overexpressed in order to effect riboflavin overproduction. Transcriptional regulation of the L. lactis riboflavin biosynthetic process was investigated by using Northern hybridization and primer extension, as well as the analysis of roseoflavin-induced riboflavin-overproducing L. lactis isolates. The latter analysis revealed the presence of both nucleotide replacements and deletions in the regulatory region of the rib operon. The results presented here are an important step toward the development of fermented foods containing increased levels of riboflavin, produced in situ, thus negating the need for vitamin fortification.Riboflavin (vitamin B 2 ) is an essential component of basic cellular metabolism since it is the precursor of the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). The latter two biomolecules play a central role in metabolism acting as hydrogen carriers in biological redox reactions involving enzymes such as NADH dehydrogenase (for a review of this topic, see reference 32). Many microorganisms, plants, and fungi possess the biosynthetic ability to produce riboflavin. However, vertebrates, including humans, lack this ability and must therefore obtain this vitamin from their diet.Dietary riboflavin is present in liver, egg yolk, milk, and meat, whereas the vitamin is commercially synthesized for nutritional use in the fortification of various food products such as bread and breakfast cereals. Because of its intense yellow color it is also used in small amounts as a coloring agent in foods such as ice cream and sauces, and as a medical identification aid. The recommended daily requirement of riboflavin is set at 1.3 mg (14) and sufficient amounts of riboflavin need to be ingested regularly since the body is unable to store the vitamin. Symptoms of riboflavin deficiency (ariboflavinosis) in humans, which still occurs in both developing and developed countries (6, 34), include sore throat, hyperemia, edema of oral and mucous membranes, cheilosis, and glossitis (48). Furthermore, riboflavin is used as a treatment for nucleoside analogue-induced type B lactic acidosis, which can occur as a result of AIDS treatment (9), for migraine (23), and for malaria (1). Commercially available riboflavin has traditionally been produced by chemical processes, but in recent times this has been replaced by biotechnological and more economical processes with Ashbya gossypii, Candida famata, or Bacillus subtilis (43).Riboflavin biosynthesis has been studied in both gram-positive and gram-negative bacteria, in most detail in B. subtilis (36) and Escherichia coli (4). Th...

Biocides play an essential role in limiting the spread of infectious disease. The food industry is dependent on these agents, and their increasing use is a matter for concern. Specifically, the emergence of bacteria demonstrating increased tolerance to biocides, coupled with the potential for the development of a phenotype of cross-resistance to clinically important antimicrobial compounds, needs to be assessed. In this study, we investigated the tolerance of a collection of susceptible and multidrug-resistant (MDR) Salmonella enterica strains to a panel of seven commercially available food-grade biocide formulations. We explored their abilities to adapt to these formulations and their active biocidal agents, i.e., triclosan, chlorhexidine, hydrogen peroxide, and benzalkonium chloride, after sequential rounds of in vitro selection. Finally, cross-tolerance of different categories of biocidal formulations, their active agents, and the potential for coselection of resistance to clinically important antibiotics were investigated. Six of seven food-grade biocide formulations were bactericidal at their recommended working concentrations. All showed a reduced activity against both surface-dried and biofilm cultures. A stable phenotype of tolerance to biocide formulations could not be selected. Upon exposure of Salmonella strains to an active biocidal compound, a high-level of tolerance was selected for a number of Salmonella serotypes. No cross-tolerance to the different biocidal agents or food-grade biocide formulations was observed. Most tolerant isolates displayed changes in their patterns of susceptibility to antimicrobial compounds. Food industry biocides are effective against planktonic Salmonella. When exposed to sublethal concentrations of individual active biocidal agents, tolerant isolates may emerge. This emergence was associated with changes in antimicrobial susceptibilities.

Ultrasound assisted extraction (UAE), purification, characterization and antioxidant activity of laminarin from Irish brown seaweeds Ascophyllum nodosum and Laminarina hyperborea were investigated. UAE was carried out using 60% ultrasonic power amplitude and 0.1 M hydrochloric acid for 15 min. Separately, solid-liquid extraction was carried in an orbital shaker using 0.1 M hydrochloric acid at 70 °C for 2.5 h. UAE with hydrochloric acid resulted in the highest concentration of laminarin, 5.82% and 6.24% on dry weight basis from A. nodosum and L. hyperborea, respectively. Purification of all extracts was carried out using molecular weight cut off dialysis at 10 kDa. Characterization of the laminarin fraction was carried out using matrix assisted laser desorption/ionization time-of-flight mass spectrometry. Antioxidant activity of A. nodosum and L. hyperborea extracts had 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition levels of 93.23% and 87.57%, respectively. Moreover, these extracts have shown inihibition of bacterial growth of Staphylcoccus aureus, Listeria monocytogenes, Escherichia coli and Salmonella typhimurium.