Herpes simplex virus type 2 modulates the susceptibility of human bladder cells to uropathogenic bacteria.

The present study analyses the susceptibility of human bladder-derived cells (HT-1376) to the infection by herpes simplex virus type 2 (HSV-2) and Chlamydia trachomatis, as well as to the adhesiveness of uropathogenic bacteria. HT-1376 cells were efficiently infected by HSV-2 strain 333, as demonstrated by immunofluorescence staining of viral antigens, titration of cytopathic effect, and visualisation by transmission electron microscopy. This cell model was also prone to C. trachomatis (serovar E, Bour strain) replication and to the adherence of clinical uropathogenic isolates of Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris and Enterococcus faecalis. The pre-infection of HT-1376 cells with HSV-2 caused a tenfold increased adherence of an E. coli strain (U1), isolated from a patient affected by severe haemorrhagic cystitis, whereas in HSV-2 pre-infected cells the number of C. trachomatis inclusion bodies was significantly reduced. Our findings indicate that these cells are a suitable in vitro model for studying infection and super-infection of the lower urinary tract by viruses and bacteria.

Involvement of bovine lactoferrin moieties in the inhibition of herpes simplex virus type 1 infection.

Bovine lactoferrin (BLf) is an iron binding protein folded in two lobes, N- and C-lobes. In this study we have reported the inhibitory activity towards herpes simplex virus type 1 (HSV-1) in vitro infection of BLf tryptic digested N- and C-lobes in comparison with the whole protein. The N-lobe and C-lobe exerted an anti-herpesvirus activity 50- and 10-fold lower than native BLf, respectively. In order to assess the phase of viral replication affected, lactoferrin-derived lobes were added to the cells at different non cytotoxic concentrations, during the whole cycle of viral infection or during viral attachment step, demonstrating that both lobes interfered with the early phases of infection. Among the BLf tryptic digested fragments, two negatively-charged small peptides deriving from N-lobe, previously shown effective towards HSV-1, have been further studied. We assessed that the net negative charge of these peptides was not responsible for the antiviral activity since their activity was not modified when the aspartic and glutamic acidic residues of these peptides were replaced with asparagine and glutamine, respectively. The experiments here reported confirm a pivotal role of N-lobe in inhibiting viral infection. However, the residual inhibiting activity of C-lobe and the similar efficacy shown by negatively or positively charged peptides strongly support the idea that the antiviral activity of bovine lactoferrin cannot be fully explained simply on the basis of competition between the protein and viral recognition sites for binding to glycosaminoglycans.

Infection of human enterocyte-like cells with rotavirus enhances invasiveness of Yersinia enterocolitica and Y. pseudotuberculosis.

Mixed infection with rotavirus and either Yersinia enterocolitica or Y. pseudotuberculosis was analysed in Caco-2 cells, an enterocyte-like cell line highly susceptible to these pathogens. Results showed an increase of bacterial adhesion and internalisation in rotavirus-infected cells. Increased internalisation was also seen with Escherichia coli strain HB101 (pRI203), harbouring the inv gene from Y. pseudotuberculosis, which is involved in the invasion process of host cells. In contrast, the superinfection with bacteria of Caco-2 cells pre-infected with rotavirus resulted in decreased viral antigen synthesis. Transmission electron microscopy confirmed the dual infection of enterocytes. These data suggest that rotavirus infection enhances the early interaction between host cell surfaces and enteroinvasive Yersinia spp.

Acid tolerance in Listeria monocytogenes influences invasiveness of enterocyte-like cells and macrophage-like cells.

Clinical and food Listeria monocytogenes isolates, pre-exposed to mild acidic conditions, were able to readily develop acid tolerance, irrespective of their origin. We attempted to investigate the influence of acid tolerance mechanisms, either constitutive or induced, on the invasive behaviour of this facultative food-borne pathogen. Entry efficiency and intracellular growth of acid-tolerant strains were evaluated in in vitro cell models capable to mimic in vivo target cells, such as enterocytes and macrophages. An acid-adapted L. monocytogenes wild-type strain and a constitutively acid-tolerant mutant were able to enter enterocyte-like (Caco-2) cells as well as to survive and proliferate intracellularly in lipopolysaccharide-treated macrophage-like (J774.A1) cells, at a significant increased extent by respect of the non acid-adapted wild-type strain. These findings add new information about the influence of the acid tolerance response on L. monocytogenes virulence, suggesting that in acid-adapted bacteria the early events of pathogenesis which allow the colonization and the spread of bacteria in the host may be highly promoted.