Indirect effects in a planktonic disease system.

Indirect effects, both density- and trait-mediated, have been known to act in tandem with direct effects in the interactions of numerous species. They have been shown to affect populations embedded in competitive and mutualistic networks alike. In this work, we introduce a four-dimensional system of ordinary differential equations and investigate the interplay between direct density-effects and density- and trait-mediated indirect effects that take place in a yeast parasite-zooplankton host-incompetent competitor system embedded in a food web which also includes resources and predators. Among our main findings is the demonstration that indirect effects cause qualitative and quantitative changes almost indistinguishable from direct effects and the corroboration through our analysis of the fact that the effects of direct and indirect mechanisms cannot be disentangled. Our results underpin the conclusions of past studies calling for comprehensive models that incorporate both direct and indirect effects to better describe field data.

Coliform bacteria, fabrics, and the environment.

BACKGROUND: People come into contact with coliform bacteria at recreational sites. Previous research on bacteria adhering to fabrics and surfaces focused on the viability of clinically significant microbes, but did not examine the quantity of bacteria. This study examined the viability and quantity of coliform bacteria adhered to common fabrics. METHODS: The fabrics of 100% cotton, blended cotton, and silk were exposed to a mixture of environmental coliform isolates. Fabrics were incubated in the dark at 25°C or 37°C or in direct sunlight at room temperature for 30, 60, 90, and 120 days. The quantity and viability of the bacteria were determined by the Most Probable Number technique using Colilert reagent (IDEXX Laboratories, Westbrook, ME) and eosin methylene blue agar, respectively. RESULTS: The highest numbers of bacteria were detected for each type of fabric when stored in the dark at 25°C, whereas the lowest numbers of bacteria were detected when fabrics were stored in the dark at 37°C. Low numbers of bacteria were detected on silk and blended cotton exposed to sunlight at room temperature, but not 100% cotton. CONCLUSION: It appears that coliform bacteria can survive on fabrics longer than previous studies have reported. Coliform bacteria survive better in the dark, at lower temperatures, and on fabrics that can retain moisture. These findings can be applied directly to the viability of bacteria on clothing and potential human exposure to fecal pathogens.

Herpes simplex virus type 1 infection induces oxidative stress and the release of bioactive lipid peroxidation by-products in mouse P19N neural cell cultures.

To determine whether herpes simplex virus type 1 (HSV-1) infection causes oxidative stress and lipid peroxidation in cultured neural cells, mouse P19 embryonal carcinoma cells were differentiated into cells with neural phenotypes (P19N cells) by retinoic acid and were then infected with HSV-1. Cellular levels of reactive oxygen species (ROS) and the release of lipid peroxidation by-products into the tissue culture medium were then measured by the generation of fluorescent markers hydroxyphenyl fluorescein and a stable chromophore produced by lipid peroxidation products, malondialdehyde (MDA) and hydroxyalkenals (4-HAEs; predominantly 4-hydroxy-2-nonenal [HNE]), respectively. HSV-1 infection increased ROS levels in neural cells as early as 1 h post infection (p.i.) and ROS levels remained elevated at 24 h p.i. This viral effect required viral entry and replication as heat- and ultraviolet light-inactivated HSV-1 were ineffective. HSV-1 infection also was associated with increased levels of MDA/HAE in the culture medium at 2 and 4 h p.i., but MDA/HAE levels were not different from those detected in mock infected control cultures at 1, 6, and 24 h p.i. HSV-1 replication in P19N cells was inhibited by the antioxidant compound ebselen and high concentrations of HNE added to the cultures, but was increased by low concentrations of HNE. These findings indicate that HSV-1 infection of neural cells causes oxidative stress that is required for efficient viral replication. Furthermore, these observations raise the possibility that soluble, bioactive lipid peroxidation by-products generated in infected neural cells may be important regulators of HSV-1 pathogenesis in the nervous system.

Herpes simplex virus entry receptor nectin-1 is widely expressed in the murine eye.

PURPOSE: Nectin-1 belongs to the immunoglobulin superfamily, mediates cell-cell adhesion in cadherin-based adherens junctions, and acts as a receptor for herpes simplex virus (HSV). The goals of this study were (1) to determine whether nectin-1 is expressed in ocular tissue that is an important target of HSV infections and (2) to determine whether HSV type 1 (HSV-1) infection affects nectin-1 expression in the eye. METHODS: Expression of nectin-1 and HSV-1 protein was determined by immunohistochemical analysis of ocular tissues of untreated BALB/c mice and mice that were euthanized either 7 days or 7 months after corneal inoculation of HSV-1 or sterile tissue-culture medium (mock). RESULTS: In ocular tissues derived from untreated and mock-infected mice, widespread nectin-1 expression was detected among cells of the corneal epithelium and endothelium, conjunctiva, lens epithelium, ciliary body, iris, choroid, and retina. However, fibroblasts in the corneal stroma and the sclera did not express detectable levels of nectin-1. Ocular tissues from mice euthanized 7 days after corneal inoculation of HSV-1 frequently demonstrated corneal ulceration and inflammation and HSV-1 protein expression in the corneal epithelium, stroma, endothelium, conjunctiva, iris, and ciliary body but rarely in the retina. Ocular tissues from mice euthanized 7 months after HSV-1 inoculation demonstrated corneal epithelial and stromal inflammation, but HSV-1 protein expression was not detected. HSV-1 infection did not lead to a loss of nectin-1 expression in any of the tissues examined. In contrast to uninfected corneas, the inflamed and vascularized stroma of infected corneas contained mononuclear inflammatory cells, vascular cells, and fibroblasts that stained positive for nectin-1. CONCLUSIONS: Findings report that nectin-1 is widely expressed in murine ocular tissues. Only fibroblasts in the corneal stroma and sclera of uninfected tissues were devoid of nectin-1 expression. HSV-1-infected inflamed corneas contained some stromal fibroblasts with detectable nectin-1 expression, which potentially could be targeted by the virus. Widespread nectin-1 expression in the eye suggests that this receptor may play a role in the pathogenesis of ocular HSV infections.

The effects of natural biofilms on the reattachment of young adult zebra mussels to artificial substrata.

This laboratory study examined the effects of natural biofilms on the reattachment of young adult zebra mussels, Dreissena polymorpha, in Petri dishes. Natural biofilms were developed in glass and polystyrene Petri dishes using water samples collected at various times of the year. Biofilms were developed over 1, 3, 8, and 14 d. Controls were clean glass and polystyrene Petri dishes. Zebra mussels collected from the field (< or = 10 mm, ventral length) were placed in the dishes and their reattachment by byssal threads was recorded after 1 d. Zebra mussels reattached to the dish surface or the shells of other mussels in the dish, or remained unattached. The data indicate that reattachment to clean glass was greater than to clean polystyrene (p < or = 0.05, ANOVA), but there were no consistent differences between reattachment to filmed polystyrene and filmed glass dish surfaces. Zebra mussels in control and filmed glass dishes reattached in higher percentages to the dish surface compared to the shells of other mussels (p < or = 0.05, ANOVA). There was no difference in mussel of reattachment between the dish surface and the shells of other mussels in most control polystyrene dishes (p > 0.05, ANOVA), whereas in filmed polystyrene the percentage of reattachment to the dish surface was greater than to the shells of other mussels (p < or = 0.05, ANOVA). These results indicate that substratum wettability and the presence of biofilms on some types of substrata can be factors in the reattachment of young adult zebra mussels.