In vitro model of adhesion and invasion by Bacillus piliformis

Lawsonia intracellularis: getting inside the pathogenesis of proliferative enteropathy

Although proliferative enteropathy (PE) has been recognised for several decades, Lawsonia intracellularis, the aetiological agent, was identified formally in only 1995. This organism is both highly fastidious and obligately intracellular bacterium, characteristics which have inevitably restricted investigations in all aspects of its biology. Despite these limitations, advances have been made in characterising and understanding L. intracellularis-host interaction both in vivo and in vitro. Based upon evidence provided by mainly pathological and histological investigations conducted to date, we review salient features of our current understanding of processes involved throughout the course of infection by this unique pathogen.

Common Diseases

Many pathogens have been reported to cause disease in the laboratory rat. This chapter concentrates on the pathology of the more common pathogens of the laboratory rat. Based on serologic surveys, parvo viruses are some of the most common viral pathogens in wild and laboratory rat. In general, there are three main serogroups, including Rat virus (RV), H-1 virus, and Ratparvovirus (RPV). Both RPV and RV are tropic for many of the same tissues and they both may result in a persistent infection. However, RPV is antigenically and genetically distinct from RV, and it apparently does not cause clinical signs or lesions in infant rats. M. pulmonis causes natural disease in rats and mice. The infection in young rats is usually clinically silent. In older rats, there are nonspecific clinical signs such as snuffling, chromodacryorrhea, and face and ear rubbing. Several bacteria of the genus Streptococcus can cause clinical disease in rats. All of the streptococci of concern in rats are Gram-positive cocci, and are catalase-negative, nonfermentative, and generally nonmotile. Cilia-associated respiratory bacillus has been identified in rats. In rats, infection is usually asymptomatic although nonspecific clinical signs, such as weight loss and dyspnea, may be observed.

Cell integrity markers for in vitro evaluation of cytotoxic responses to bacteria-containing commercial insecticides

Toxicity of two commercial "BT" products, containing Bacillus thuringiensis subsp. kurstaki spores (Btk) and associated parasporal inclusion body proteins, was tested in vitro using two unrelated lepidoperan cell lines and several markers of cell integrity (morphology, quantification of loss of adherence and electron transport (redox) activity, and degradation of nuclear DNA, actin, hsp-70, and beta-tubulin). With doses of 10(-7), 10(-5), and 10(-3) International Units (IU)/target cell, these markers measured exposure-dependent effects closely linked to cell death, which occurred rapidly once Btk spores germinated, unless inhibited by antibiotic. Derivation of marker half-lives (HL50) revealed that temperature critically affected product performance. Between 34 and 37 degrees C, HL50 was < or = 5 hr, but dose discrimination between 10(-5) and 10(-3) IU was poor. At temperatures less than 34 degrees C, the resolution between different HL50s and doses increased in a manner directly relating to published data obtained from in vivo BT-spore-induced LD50 assays. It was concluded that BT product toxification is complex, essentially enabled by an autobiotransformation process in which dose-response lag is affected by temperature-dependent temporal expression of spore germination and critical buildup of vegetative cells and byproduct toxicants. The in vitro dosimetry assays described here are potentially useful for obtaining mechanistic toxicologic data and in vivo relevant quantifications of subingredient activities in various commercial BT formulations as well as in other microbe-based biotechnology products.

Effects of neutrophil, natural killer cell, and macrophage depletion on murine Clostridium piliforme infection

Clostridium piliforme infection (Tyzzer's disease) induces enterohepatic disease in many domestic and laboratory animals. Murine susceptibility to Tyzzer's disease varies with host strain, age, and immune status However, little is known about the role of the immune system in control of this disease. To investigate the role of host immunity in Tyzzer's disease, mice were depleted of either neutrophils, natural killer cells, or macrophages by antibody administration or chemotherapy. After depletion, DBA/2 mice, which are naturally susceptible to C. piliforme, or naturally resistant C57BL/6 mice were inoculated intravenously with C. piliforme. Animals were euthanized 3 days postinoculation and evaluated for gross and histologic lesions and hepatic bacterial load. In juvenile DBA/2 or C57BL/6 mice, depletion of either neutrophils or natural killer cells increased severity of disease. In adult mice, depletion of natural killer cells significantly increased severity of Tyzzer's disease in the resistant (C57BL/6) but not in the susceptible (DBA/2) strain. Macrophage depletion did not alter the course of infection in either mouse strain. These studies indicate an important role for neutrophils and natural killer cells in the pathogenesis of murine Tyzzer's disease. The role of macrophages in murine C. piliforme infection will require further evaluation.

Semiautomated quantification of cytotoxic damage induced in cultured insect cells exposed to commercial Bacillus thuringiensis biopesticides

A convenient in vitro bioassay based on semiautomated quantification of live-cell reduction of tetrazolium dyes--3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and 2,3-bis(2-methoxy-4-nitro-5-sulphophenyl)-2H-tetrazolium-5-corb oxanilide sodium salt (XTT)--to formazan was developed and used to evaluate cytotoxic effects of two commercial insecticides (BT) derived from Bacillus thuringiensis subsp. kurstaki (Btk). Comparison of two target insect cell lines MG1 (Trichoplusia ni, cabbage looper midgut) and Sf9 (Spodoptera frugiperda, fall army worm oocyte) revealed similar cell-dependent responses in mitochondrial-associated electron transport activity. The 50% inhibition of formazan production (ID50) obtained by exposing these cells to 20 microM 2,4-dinitrophenol or 5 mM sodium azide occurred in the range 10(-7)-10(-6) International Units (IU) of BT cell(-1) 24 h(-1). Damage to cell adhesion and cytoarchitecture, revealed by light and electron microscopic analysis, increased with BT exposure and dose. MTT was superior to XTT as a cytotoxic indicator in kinetic studies related to spores, a major component of BT. Unless blocked by antibiotic (gentamicin), vegetative growth resulting from spore germination was the major cause of toxicity. The ID50 exposure time using vegetative Btk cells was approximately 0.1-0.2 times that required for BT spores, with or without intact parasporal proteins present. This difference in exposure is an indirect measure of the time required for spores to germinate and produce vegetative cells. The assay methodology developed here, if linked with suitable target and non-target animal cell types, should have broad application for conducting standardizable estimates of cytotoxic potential of any microbe-based biotechnology product.

Aggregative adherence of Klebsiella pneumoniae to human intestine-407 cells

Aggregative adhesion of Klebsiella pneumoniae LM3 to Intestine-407 (Int-407) cells was studied. Adhesive capacities were affected by the bacterial growth phase (with a maximum of adherence obtained during the exponential phase), temperature, multiplicity of infection, and length of incubation with Int-407 cells. Adhesion occurred through a cytochalasin D-sensitive process and was greatly reduced after treatment of Int-407 with cycloheximide, indicating that aggregative adhesion requires active participation of Int-407 cells. Transmission electron microscopy revealed that adherent bacteria were surrounded by a capsule-like material, apparently involved in both bacterium-Int-407 cell and bacterium-bacterium adherence. Examination with a scanning electron microscope showed interactions of intestinal cell microvilli with bacteria and formation in 3 h of a fibrous network within and around the bacterial clusters. We speculate that aggregative adhesion of K. pneumoniae mediated by a capsule-like extracellular material might explain the persistence of these strains inside the host gastrointestinal tract.

A fluorescence-based quantitative adhesion assay to study interactions between Entamoeba histolytica and human enterocytes. Effect of proinflammatory cytokines

In order to study the initial events during infection of target cells by the enteric pathogen Entamoeba histolytica, we developed a quantitative adhesion assay based on the use of a human colonic cell line (CaCo-2) and biotinylated amoebae tagged with fluorescein. To prevent the strong and rapid lytic activity of Entamoeba histolytica on colonic cells, which would otherwise impede the study of the primary adhesion steps, parasites were mildly fixed, biotinylated and labelled with streptavidin-FITC. After labelled parasites have bound to enterocytes, nonadhered amoebae are removed by washing and attached parasites quantified by means of an automated fluorescence plate reader. The bioassay is simple, nonhazardous and can be completed in 1.5 h. We were able to detect ranges from 200 to 20,000 fluorescent parasites per microwell in a 96-well plate, containing approximately 10(5) colonic cells. Fluorescence intensity (arbitrary units) increased in direct relationship to the number of parasites added per well, and was not limited by the size of the culture plate (96, 24 or six wells). As an example of the value of this assay, two proinflammatory cytokines (interleukin-1, (IL-1 beta) and interferon-gamma (IFN-gamma) known to influence the adhesion properties of endothelial and epithelial cells, were used to assess their effects upon enterocyte-entamoeba binding. The increase in amoebae binding revealed by cytokine treatment to enterocytes suggests that the parasite may take advantage of inflammatory stimuli in order to increase its binding to colonic epithelium. We believe this rapid, sensitive and simple method offers the potential for large scale screening assays to study the immunobiology of this protozoal infection by analysing the mechanisms involved in the primary interactions between Entamoeba histolytica and enterocytes.