Clonal diversity and host distribution in Bordetella bronchiseptica.

A total of 303 isolates of Bordetella bronchiseptica recovered from 11 host species were characterized by the electrophoretic mobilities of 15 metabolic enzymes, and 21 distinctive multilocus genotypes (electrophoretic types) were distinguished on the basis of allele profiles at the enzyme loci. The population structure of B. bronchiseptica is clonal, and its genetic diversity is limited in comparison with most other pathogenic bacteria, perhaps reflecting a relatively recent origin of the species. Electrophoretic types mark clones which are, in many cases, nonrandomly associated with host species. Clones differing only slightly in overall chromosomal genetic character may have pronounced differences in virulence potential. There was considerable variation among individual clones and clone families in degree of host specificity and among various species of hosts in the diversity of clones causing disease. The diversity of clones infecting dogs was an order of magnitude greater than that of clones infecting pigs. Most bordetellosis in pigs in the United States and Japan was found to be caused by strains of a single multilocus genotype.     

Intestinal distribution of worms and host ingesta in Nippostrongylus brasiliensis.

The gastrointestinal nematode Nippostrongylus brasiliensis is thought to feed on host ingesta, and it is generally thought that the presence of ingesta determines the distribution of this parasite within the host intestine. However, these assertions have not been supported by direct evidence. The purpose of this study was to test the hypothesis that N. brasiliensis worms are preferentially found in regions of the host small intestine containing ingesta. The relationship between worm and ingesta distribution was investigated using mice infected with N. brasiliensis and killed on day 8 postinfection at 0130, 0730, 1330, or 1930 hr. There was an inverse relationship between worm and ingesta distributions, and the worms were distributed significantly more anteriad in the intestine than host ingesta, at all times during the 24 hr. To determine what the worms fed on, host ingesta, tissue, and blood were differentially labeled with the fluorescent dyes rhodamine B and Fluoresbrite. The results of this study suggest that N. brasiliensis feeds on the host's intestinal wall, and that habitat distribution of this parasite within the small intestine is not directly related to the presence of luminal ingesta.     

The role of fever in the infected host

Sepsis is a highly lethal clinical syndrome characterized by a systemic inflammatory response to infection. Fever, a non-specific acute-phase response, has been associated with improved survival and shortened disease duration in non-life-threatening infections. However, the influence of fever and the effects of antipyresis in patients with sepsis has not been prospectively studied in humans. This paper reviews the state of our knowledge concerning the biological effects of fever in infected hosts and the influence of fever and antipyretic therapy on survival during sepsis in experimental models and in man.     

Heterogeneity of Salmonella-host interactions in infected host tissues

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Comparison of initiation rates of encephalomyocarditis virus and host protein synthesis in infected cells.

The relative initiation rates for encephalomyocarditis virus mRNA and host mRNA's in infected cells were measured using two independent techniques. In both cases the results showed that viral mRNA initiates at a much higher rate than host mRNA'S. This difference was observed midway in the infectious cycle, well before virus-induced cytopathic effects (leakage of low-molecular-weight metabolites, failure to exclude trypan blue) were apparent. These results confirm that encephalomyocarditis viral mRNA is a more efficient initiator than host mRNA's in vivo, as has previously been demonstrated in in vitro experiments.     

Nest site selection and predation driven despotic distribution of breeding long-eared owls Asio otus

Long-eared owls Asio otus do not build their own nests. They occupy old corvid nests in either coniferous or deciduous trees. In my study area owls favoured coniferous over deciduous trees for nesting and occupied nest sites in that order. Comparing overall breeding output, I found no difference between the two kinds of nest sites, but among early nests there was a higher proportion of unsuccessful nests in deciduous trees. This difference was due to differences in predation rate, indicating that the owls' pattern of nest site occupation followed predictions from the ideal despotic distribution model. I also show that, due to a seasonal change in habitat quality, predator driven despotism, although present, can be well masked and hence difficult to detect.     

Expression of host genes in influenza virus infected cells

The NS1 protein of influenza virus shuts off host gene expression by inhibiting the polyadenylation-site cleavage of host pre-mRNAs, resulting in a general decline in cellular protein synthesis. On the other hand, an activation of several host genes related to host antiviral defense such as interferon- alpha/beta, MxA, 2',5'-oligoadenylate synthetase, and Fas occures upon infection. Therefore, balance of the shut-off and the activation of cellular genes during virus growth may be crucial in determining the outcome of infection. To obtain a comprehensive view of the global effects of influenza virus infection on human respiratory epithelial cells at the cytoplasmic mRNA level, we performed oligo DNA microarray analysis using GeneChip arrays (Affymetrix). In NCl-H292 cells infected with A/Udorn/72 virus, more than 4-fold increase of expression level was observed for 164 genes at 12 h pi. Approximately 60% of the virus-stimulated genes (VSGs) were also stimulated with interferon-beta treatment and contained the genes known to possess antiviral activity. Interestingly, majority of the VSGs were stimulated before induction of interferons, suggesting that the stimulation of the VSGs during early phase of infection is not mediated by interferons, but it is triggered from within by the virus infection.     

Systematics, distribution, and host specificity of grass endophytes.

Clavicipitaceous endophytes (Ascomycetes) are distributed worldwide in many grasses and sedges forming a perennial and often mutualistic association with their hosts. Most endophytes appear to produce alkaloid toxins in infected plants. The high frequency of infection in many grasses and in certain grassland communities may indicate a selective advantage of infected over non-infected host plants due to their toxic effects on grazing animals and insects. Field observations and artificial inoculations of seedlings have demonstrated a high degree of specificity of most endophytes to their host plant, particularly in asexual, seed-borne endophytes. Specific isozyme genotypes found on several host species suggest that host-specific physiological races may occur. Knowledge of host range and host specificity is vital for potential applications of endophytes in pest control.     

Common host antigens in laboratory rats infected with the metacestodes of Taenia crassiceps.

Laboratory rats were infected by intra-peritoneal injection with the metacestodes of Taenia crassiceps. A soluble extract was prepared from the metacestodes removed from the peritoneal cavity of the rats. Double-diffusion, immuno-electrophoresis and fluorescent labelled antibody staining techniques were used. The extract tested against rabbit anti-normal rat serum was found to contain an antigen common to both the host and the parasite.     

Damage distribution and mutation spectrum: the case of 8-methoxypsoralen plus UVA in mammalian cells.

We determined the distribution of monoadducts and biadducts induced in the supF tRNA gene carried by the shuttle vector pZ189, after exposure to 8-methoxypsoralen (8-MOP) plus a double UVA (365 nm) irradiation. These data were compared to our previously published 8-MOP-photoinduced mutation spectrum obtained after propagation of the damaged shuttle vector in mammalian cells. One mutational hot spot in an ATAT/TATA sequence is targeted at a hot spot of biaddition. A second hot spot is not related to the presence of photoadducts either at or near the site. Moreover, it is located in a sequence which can be defined as 'mutation-prone'. Mutations occurring at GC base pairs are not targeted at sites of photoaddition, and may result from a decrease in fidelity of DNA polymerase when copying the damaged vector.     

The evolution of endosymbiont density in doubly infected host species

Multiple infection of individual hosts with several species or strains of maternally inherited endosymbionts is commonly observed in animals, especially insects. Here, we address theoretically the effect of co-infection on the optimal density of the endosymbionts in doubly infected hosts. Our analysis is based on the observation that a maternally inherited double infection is only stable if doubly infected females produce more doubly infected daughters than singly infected or uninfected females produce daughters. We consider both a general model and a model involving two endosymbionts inducing bidirectional cytoplasmic incompatibility (CI). We demonstrate that the optimal replication rate of endosymbionts in doubly infected hosts can be expected to be similar to or below the optimal replication rate in singly infected hosts. This is in contrast to some theoretical predictions for horizontally transmitted parasites and stems from the two strains of endosymbionts having coupled fitness. We discuss our results with respect to recent empirical results on endosymbiont densities, the evolution of CI-inducing bacteria and, more generally, the evolution of cooperation through direct fitness benefits.     

Genotoxicity of barley stripe mosaic virus in infected host plants

A comparative study of the effect of barley stripe mosaic virus (BSMV) and gamma irradiation on mitotic divisions in barley (Hordeum vulgare L.) roots was performed by evaluating the mitotic index (MI), micronucleus (MN) frequency and sister chromatid exchanges (SCE). Results indicate that, similarly to gamma irradiation at doses of 100, 150 and 250 Gy, BSMV reduces the mitotic activity, increases the micronucleus frequency and the rate of SCE and promotes the formation of C-metaphases. In root meristematic cells of the three barley cultivars studied (Galactic, Sonor and Unirea), the mitotic index of infected plants was found to be 52.5, 54.48 and 64.17%, respectively, lower than the uninfected control. An increase in frequency of sister chromatid exchanges was observed in all the experimental variants. In treatments involving viral infection alone or in combination with gamma irradiation chromosomes with three and more chromatid exchanges were observed, while their percentage in the control or in treatments with gamma irradiation alone was reduced. The results of the study indicate that in plants derived from irradiated seeds, BSMV produces an effect that is correlated nonlinearly with the radiation dose applied. Cytological analysis of mitotic divisions in barley roots revealed the genotoxicity of BSMV infection.     

Distribution of fungal endophyte genotypes in doubly infected host grasses

Fungal endophytes of the genus Epichloë live intercellulary in above ground plant parts of many pooid ‘grasses of the temperate regions. The associations are characterized by single genotype entities since a given host individual normally contains a single endophyte genotype. They can persist over the life span of the hosts. This study examines whether two fungal genotypes can co-exist within a host plant, and how fungal genotypes are distributed within a host in the case of double infections. We selected four Epichloë bromicola strains that we identified as unique genotypes through RAPD‘ analysis. Young Bromus erectus plants, derived from callus cultures, were artificially inoculated with all possible double-strain mixtures of these fungal genotypes. For identification of fungal genotypes in planta, we designed genotype-specific primer pairs that flanked size-variable loci in the fungal genomes. Diagnostic PCR revealed that only one fungal genotype was present in most inoculated plants, but double infections were also observed with a frequency of 8% of all infected plants. Subsequent analyses of individual tillers of doubly infected plants revealed that, in a given tiller, both the leaf-blade and the leaf-sheath were colonized with only one endophyte genotype. Tillers without any detectable fungal DNA were also observed. Thus, co-existence of multiple endophyte genotypes within a single host plant is governed by mutual exclusion at the tiller level.     

Comparison of synonymous codon distribution patterns of bacteriophage and host genomes.

Synonymous codon usage patterns of bacteriophage and host genomes were compared. Two indexes, G + C base composition of a gene (fgc) and fraction of translationally optimal codons of the gene (fop), were used in the comparison. Synonymous codon usage data of all the coding sequences on a genome are represented as a cloud of points in the plane of fop vs. fgc. The Escherichia coli coding sequences appear to exhibit two phases, "rising" and "flat" phases. Genes that are essential for survival and are thought to be native are located in the flat phase, while foreign-type genes from prophages and transposons are found in the rising phase with a slope of nearly unity in the fgc vs. fop plot. Synonymous codon distribution patterns of genes from temperate phages P4, P2, N15 and lambda are similar to the pattern of E. coli rising phase genes. In contrast, genes from the virulent phage T7 or T4, for which a phage-encoded DNA polymerase is identified, fall in a linear curve with a slope of nearly zero in the fop vs. fgc plane. These results may suggest that the G + C contents for T7, T4 and E. coli flat phase genes are subject to the directional mutation pressure and are determined by the DNA polymerase used in the replication. There is significant variation in the fop values of the phage genes, suggesting an adjustment to gene expression level. Similar analyses of codon distribution patterns were carried out for Haemophilus influenzae, Bacillus subtilis, Mycobacterium tuberculosis and their phages with complete genomic sequences available.     

Novel approaches to monitor bacterial gene expression in infected tissue and host

Elucidating the complex and dynamic host-microbe interactions during infection requires, among other things, detailed knowledge of microbial gene expression in vivo. Recently, advances in fluorescence and bioluminescence detection techniques, as well as recombinase-based in vivo expression technology, have rendered monitoring virulence gene expression in vivo a feasible task. These techniques have been adapted by several laboratories to study the spatial and temporal patterns of virulence gene expression by organisms such as Salmonella typhimurium, Listeria monocytogenes, Yersinia entercolitica and Vibrio cholerae during infection of tissue culture or animal models of infection.     

The intermediate host spectrum in a Sarcocystis species of birds

The life cycle of an avian Sarcocystis has been completed in the laboratory, originating with naturally infected icterids and passing alternately between opossums (Didelphis virginiana) and experimentally infected birds. To determine the intermediate host range, six avian species, including canaries (Serinus canarius), zebra finches (Poephila guttata), budgerigars (Melopsittacus undulatus), pigeons (Columba livia), chickens (Gallus gallus), and guinea fowl (Numida meleagris), were inoculated orally with Sarcocystis sporocysts derived from experimentally infected opossums. All birds but the Galliformes were susceptible to merogony. Pigeons (Columbiformes) were susceptible to early merogony but apparently not to muscle stages. Passeriformes and Psittaciformes were completely susceptible and the parasite developed into muscle cysts in them.