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It has been suggested that the rarity of human listeriosis due to Listeria ivanovii reflects not only host tropism factors but also the rare occurrence of this species in the environment, compared with Listeria monocytogenes. In the present study we evaluate the effects on the reference strain L. ivanovii ATCC 19119 behaviour of two combined stresses, low iron availability and acid environment, that bacteria can encounter in the passage from saprophytic life to the host. In these conditions, L. ivanovii evidenced a different behaviour compared to L. monocytogenes exposed to similar conditions. L. ivanovii was not able to mount an acid tolerance response (ATR) even if, upon entry into the stationary phase in iron-loaded medium, growth phase-dependent acid resistance (AR) was evidenced. Moreover, bacteria grown in iron excess and acidic pH showed the higher invasion value in Caco-2 cells, even though it was not able to efficiently multiply. On the contrary, low iron and acidic conditions improved invasion ability in amniotic WISH cells., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Lactoferrin, a member of the transferrin family, is a bi-globular iron binding glycoprotein, found in milk, exocrine secretions of mammals, and in secondary granules of polymorphonuclear neutrophiles that plays an important role in the defence against various pathogenic microorganisms. Previous studies in different virus-cell systems showed that lactoferrin is a potent inhibitor of different enveloped and naked virus infection. In this research we studied the effect of lactoferrin on BK polyomavirus, a human naked double-stranded DNA virus responsible for productive, persistent, and latent infections of the urinary tract. Results obtained demonstrate that lactoferrin treatment prevents early steps of BK virus infection in Vero cells, at the level of the adsorption phase, probably through the interaction with capsidic structures, although a lactoferrin-BK virus competition for cell plasma-membrane receptors cannot be ruled out.

This paper describes the ability of human and bovine lactoferrins (HLf; BLf), iron-binding proteins belonging to the non-immune defense system, to interfere with herpes simplex virus type 1 (HSV-1) infection. Since lactoferrins are known to bind to heparan sulphate proteoglycans and to low density lipoprotein receptor, which in turn act as binding sites for the initial interaction of HSV-1 with host cells, we tested the effect of these proteins on HSV-1 multiplication in Vero cells. Both HLf and BLf are found to be potent inhibitors of HSV-1 infection, the concentrations required to inhibit the vital cytopathic effect in Vero cells by 50% being 1.41 microM and 0.12 microM, respectively. HLf and BLf exerted their activity through the inhibition of adsorption of virions to the cells independently of their iron withholding property showing similar activity in the apo- and iron-saturated form. The binding of [35S]methionine-labelled HSV-1 particles to Vero cells was strongly inhibited when BLf was added during the attachment step. BLf interacts with both Vero cell surfaces and HSV-1 particles, suggesting that the hindrance of cellular receptors and/or of viral attachment proteins may be involved in its antiviral mechanism.

The invasive capacity of streptococcal strains belonging to groups A and B was evaluated by infecting human epithelial and endothelial cells and monitoring the number of viable intracellular bacteria at different times postinfection. All strains tested entered eukaryotic cells (HeLa, HEp2 and HUVE), with Streptococcus pyogenes exhibiting a higher invasion efficiency than group B streptococci (GBS). No intracellular multiplication was observed, and GBS remained viable 24 h postinfection, whereas S. pyogenes were gradually killed. We found that cytochalasin D almost completely inhibited internalization of all bacterial strains, whereas colchicine had no effect, indicating that host microfilaments play a major role in bacterial internalization. Moreover, the use of the lysosomotropic agent ammonium chloride enabled us to demonstrate that a pH increase in the intracellular vesicles did not affect streptococcal entry. These results were documented by electron microscopic observations which revealed the different steps in the invasion pathway, including a fusion event between phagosomes containing S. pyogenes and lysosomes.

The aim of the present study was to evaluate the role of temperature in the virulence of Listeria monocytogenes, a Gram-positive facultative intracellular food-borne pathogen. The capacity of bacteria grown at 37, 25 and 4 degrees C to develop haemolytic activity, to enter the Caco-2 enterocyte-like cell line and to multiply intracellularly was investigated. We demonstrated that L. monocytogenes penetration was not significantly influenced by the growth temperature of cultures and that bacteria grown at low temperature were capable of synthesizing internalin and, during the infection process, of restoring the haemolytic phenotype which is normally lacking in the extracellular environment at 4 and 25 degrees C. It can be concluded that L. monocytogenes, frequently present in numerous environmental sources and also in refrigerated food products, produces at low temperature, the virulence factors necessary to invade intestinal cells.