Inhibition of foodborne bacteria by the lactoperoxidase system in a beef cube system.

Biopreservatives are being developed to inhibit the growth of foodborne pathogens and thus improve food safety. The lactoperoxidase system (LPS) is a naturally occurring system that has potential for use as an antimicrobial agent in foods. Growth of single strains of the pathogens Staphylococcus aureus, Listeria monocytogenes, Escherichia coli O157:H7, Salmonella enterica subsp. enterica serovar Typhimurium, Yersinia enterocolitica, Pseudomonas aeruginosa and beef microflora were assessed on LPS-treated meat surfaces in an experimental system. Beef cubes inoculated with approximately 10(4) cfu cm(-2) of bacteria were treated with the LPS and incubated at 37 degrees C for 24 h, 12 degrees C for 7 days or in a chilling regime: 12 to -1 degrees C over 1 week and held at -1 degrees C for 4 weeks. Treatment with LPS was more effective at storage temperatures non-permissive for rapid bacterial growth with strong inhibition of growth achieved on LPS-treated cubes at 12 degrees C and reduction in pathogen viable counts at chilling temperatures. At chilling temperatures, the LPS inhibited the growth of native pseudomonads but did not prevent the development of native lactic acid bacteria.

Inhibition of bacterial foodborne pathogens by the lactoperoxidase system in combination with monolaurin.

The lactoperoxidase system (LPS) and monolaurin (ML) are potential natural antimicrobial agents for use in foods. The LPS is considered to have greatest activity against Gram-negative bacteria while ML is usually considered to have greatest activity against Gram-positive bacteria. An LPS-ML combination system (utilizing lactoperoxidase (LPX) in the range 5-200 mg kg(-1) and ML in the range 50-1,000 ppm) inhibited growth of Escherichia coli O157:H7 and Staphylococcus aureus. Growth of S. aureus was inhibited more strongly in broth than in milk, in milk than in ground beef A similar pattern was observed for E. coli O157:H7, though enhanced inhibition by LPS-ML systems over that obtained in comparable LPS only systems was not observed in ground beef The inhibitory action of the LPS in combination with other lipids was also examined, with progressively weaker inhibition observed in combinations including palmitoleic acid, monopalmitolein, lauric acid, caprylic acid, and sodium lauryl sulphate.

Novel properties of the protein kinase CK2-site-regulated nuclear- localization sequence of the interferon-induced nuclear factor IFI 16.

Members of the interferon-induced class of nuclear factors possess a putative CcN motif, comparable with that within proteins such as the simian virus 40 large tumour antigen (T-ag), which confers phosphorylation-mediated regulation of nuclear-localization sequence (NLS)-dependent nuclear import. Here we examine the functionality of the interferon-induced factor 16 (IFI 16) CcN motif, demonstrating its ability to target a heterologous protein to the nucleus, and to be phosphorylated specifically by the CcN-motif-phosphorylating protein kinase CK2 (CK2). The IFI 16 NLS, however, has novel properties, conferring ATP-dependent nuclear import completely independent of cytosolic factors, as well as binding to nuclear components. The IFI 16 NLS is not recognized with high affinity by the NLS-binding importin heterodimer, and transport mediated by it is insensitive to non-hydrolysable GTP analogues. The IFI 16 NLS thus mediates nuclear import through a pathway completely distinct from that of conventional NLSs, such as that of T-ag, but intriguingly resembling that of the NLS of the HIV-1 transactivator protein Tat. Since the IFI 16 CK2 site enhances nuclear import through facilitating binding to nuclear components, this represents a novel mechanism by which the site regulates nuclear-protein import, and constitutes a difference between the IFI 16 and Tat NLSs that may be of importance in the immune response.

Low pH-induced cytopathic effect--a survey of seven hantavirus strains.

Hantaviruses do not produce cytopathic effects (CPE) in cell culture. However, a syncytial CPE can be induced in 7-day cultures of hantavirus growing in Vero E6 cells by reduction of the pH to approximately 6.2 using a HEPES based buffer. The appearance of this acid induced CPE was examined for seven different hantavirus strains. The differences noted were striking and reflected the taxonomic differences between hantaviruses. At 10-100 TCID50% the size of syncytial foci was very large for Seoul type viruses and smallest for Puumala viruses. The size of syncytia for Hantaan (HTN) virus was intermediate between Puumala (PUU) and Seoul (SEO) type viruses.

A consensus cAMP-dependent protein kinase (PK-A) site in place of the CcN motif casein kinase II site simian virus 40 large T-antigen confers PK-A-mediated regulation of nuclear import.

The regulation of nuclear protein transport by phosphorylation plays a central role in gene expression in eukaryotic cells. We previously showed that nuclear import of SV40 large tumor antigen (T-ag) fusion proteins is regulated by the CcN motif, comprising phosphorylation sites for casein kinase II and the cyclin-dependent kinase cdc2, together with the nuclear localization signal. Regulation of nuclear uptake by CcN motif kinase sites also holds true for the yeast transcription factor SWI5 and the Xenopus nuclear phosphoprotein nucleoplasmin. To test directly whether a kinase site other than those of the CcN motif could regulate nuclear import of T-ag, the CcN motif casein kinase II site, which markedly increases the rate of T-ag nuclear import, was replaced by a consensus site for the cAMP-dependent protein kinase (PK-A) using site-directed mutagenesis. The resultant fusion protein could be specifically phosphorylated by PK-A in vitro and in cell extracts. Nuclear import of the fluorescently labeled protein was analyzed in the HTC rat hepatoma cell line both in vivo (microinjected cells) and in vitro (mechanically perforated cells) in the presence and the absence of cAMP and/or PK-A catalytic subunit using confocal laser scanning microscopy. In vitro PK-A-prephosphorylated protein was also tested. All results indicated that the rate of nuclear import was increased by phosphorylation at the PK-A site (2-5-fold), demonstrating that kinases other than those of the CcN motif can regulate nuclear import in response to stimulatory signals. The phosphorylation-regulated nuclear localization signal derived here represents an important first step toward developing a signal conferring inducible nuclear targeting of molecules of interest.