Pathogenesis of encephalitis induced in newborn mice by virulent and avirulent strains of Sindbis virus.

Strains of Sindbis virus differ in their virulence for mice of different ages; this variation is related in large part to variations in the amino acid compositions of E1 and E2, the surface glycoproteins. The comparative pathogenesis of Sindbis virus strains which are virulent or avirulent for newborn mice has not been previously examined. We have studied the diseases caused by a virulent wild-type strain, AR339, and two less virulent laboratory strains, Toto1101 and HRSP (HR small plaque). After peripheral inoculation of 1,000 PFU, AR339 causes 100% mortality within 5 days (50% lethal dose [LD50] = 3 PFU) while Toto1101 causes 70% mortality (LD50 = 10(2.4) PFU) and HRSP causes 50 to 60% mortality (LD50 = 10(5.1) PFU) with most deaths occurring 7 to 11 days after infection. However, after intracerebral inoculation of 1,000 PFU, Toto1101 is virulent (100% mortality within 5 days; LD50 = 4 PFU) while HRSP is not (75% mortality; LD50 = 10(4.2) PFU). After intracerebral inoculation, all three strains initiate new virus formation within 4 h, but HRSP reaches a plateau of 10(6) PFU/g of brain while Toto1101 and AR339 replicate to a level of 10(8) to 10(9) PFU/g of brain within 24 h. Interferon induction parallels virus growth. Mice infected with HRSP develop persistent central nervous system infection (10(6) PFU/g of brain) until the initiation of a virus-specific immune response 7 to 8 days after infection when virus clearance begins. The distribution of virus in the brains of mice was similar, but the virus was more abundant in the case of AR339. HRSP continued to spread until day 9. Clearance from the brain was complete by day 17. We conclude that the decreased virulence of HRSP is due to an intrinsic decreased ability of this strain of Sindbis virus to grow in neural cells of the mouse. We also conclude that CD-1 mice do not respond to the antigens of Sindbis virus until approximately 1 week of age. This lack of response does not lead to tolerance and persistent infection but rather to late virus clearance whenever the immune response is initiated.     

Comparative whole-genome analysis of virulent and avirulent strains of Porphyromonas gingivalis

We used Porphyromonas gingivalis gene microarrays to compare the total gene contents of the virulent strain W83 and the avirulent type strain, ATCC 33277. Signal ratios and scatter plots indicated that the chromosomes were very similar, with approximately 93% of the predicted genes in common, while at least 7% of them showed very low or no signals in ATCC 33277. Verification of the array results by PCR indicated that several of the disparate genes were either absent from or variant in ATCC 33277. Divergent features included already reported insertion sequences and ragB, as well as additional hypothetical and functionally assigned genes. Several of the latter were organized in a putative operon in W83 and encoded enzymes involved in capsular polysaccharide synthesis. Another cluster was associated with two paralogous regions of the chromosome with a low G+C content, at 41%, compared to that of the whole genome, at 48%. These regions also contained conserved and species-specific hypothetical genes, transposons, insertion sequences, and integrases and were located adjacent to tRNA genes; thus, they had several characteristics of pathogenicity islands. While this global comparative analysis showed the close relationship between W83 and ATCC 33277, the clustering of genes that are present in W83 but divergent in or absent from ATCC 33277 is suggestive of chromosomal islands that may have been acquired by lateral gene transfer.     

Expression of antigens in virulent and avirulent Indian strains ofLeishmania donovani

Indo-Gen mediated surface labelling with¹²⁵I demonstrated differences in surface oriented antigens between virulent and virulent promastigote ofLeishniania donovani, In case of virulent strains, surface polypeptides with molecular masses of 63, 53, 42 and 38 kDa were found to be labelled with¹²⁵I whereas in the case of aviralent stains 68, 55, 50, 46, 42 and 33 Da, components were iodinated. Further studies by immunoblot assay using different subcellular fractions of virulent and avirulent parasites demonstrated that antibody raised against gp63 cross-reacted with the 63 and 60 kDa antigen of the virulent and avirulentLeishmania donovani strains of Indian origin respectively. It indicates that these two polypeptides are antigenically similar. When virulent and avirulent cells were grown in the presence of varying concentration of tunicarnycin and immunoblot with anti gp63, it was observed that with increasing concentration of tunicamycin the 63 kDa polypeptide of the virulent cells shifted to approximately 58–57 kDa and the 60 kDa polypoptide of the aviruleni cells shifted to 57 kDa. This suggests that glycosylation may play an important role in antigenic variation between virulent and avirulent parasites.     

A comparative study of virulent and avirulent strains of Chromobacterium violaceum

A clinical isolate and a soil isolate of Chromobacterium violaceum were compared to determine differences in virulence-related characteristics. Purified lipopolysaccharide (endotoxin) from the virulent, clinical strain was more reactive than that from the avirulent soil strain as determined by the Limulus amebocyte lysate assay. There were no differences in hemolysin or cyanide production between the two strains. The virulent strain was more resistant to phagocytosis and intracellular killing by human polymorphonucleocytes. The clinical strain showed a superoxide dismutase activity 30% higher and a catalase activity fivefold higher than the activities of the soil-isolated strain. The clinical strain also was capable of producing approximately twice as much hydrogen peroxide during growth as compared with the soil isolate. This study suggests that virulence of C. violaceum may be, at least in part, associated with endotoxin, and some protection of the virulent, clinical strain from phagocytic attack is afforded by elevated levels of superoxide dismutase and catalase.     

Colonization of turbot tissues by virulent and avirulent Aeromonas salmonicida subsp. salmonicida strains during infection

Preventing disease outbreaks in cultured turbot Psetta maxima L. caused by Aeromonas salmonicida subsp. salmonicida (ASS) requires a better understanding of how this pathogen colonizes its host. Distribution of 1 virulent and 2 avirulent ASS strains in turbot tissues was investigated during early and late stages of infection following an immersion challenge. To track bacteria within the turbot, the ASS strains were tagged with green fluorescent protein (GFP). Both virulent and avirulent strains colonized the epidermal mucus, gills, and intestine within the first 12 h post challenge, suggesting that these sites may serve as points of entry into turbot. Although the avirulent strains colonized these initial sites in the turbot tissues, they were rarely found in the internal organs and were cleared from the host 4 d post challenge. In contrast, the virulent ASS strain was found in the liver and kidney as early as 12 h post challenge and was found in the muscle tissue at very late stages of infection. The virulent strain persisted in all tested host tissues until death occurred 7 d post challenge, suggesting that ASS must colonize and survive within the turbot tissues for an infection to result in death of the fish. Comparisons of the distribution profiles of both virulent and avirulent strains during early and late stages of an infection in turbot has provided important information on the route and persistence of an ASS infection in this host.     

A 78-megadalton plasmid occurs in avirulent strains as well as virulent strains ofCorynebacterium fascians

Ten wild-type strains ofCorynebacterium fascians, which differed in degree of virulence as measured by ability to cause hyperplasias (multiple stems; fasciation) in pea seedlings, were examined for the presence of plasmids. Four strains were highly virulent, three were avirulent, and three were intermediate in virulence. All of these wild-type strains harbored one plasmid each of approximately 78 megadaltons, as estimated from electrophoretic mobilities in agarose gels capable of resolving reference plasmids ranging from 8.8 to 350 Mdal. Restriction endonuclease (EcoRI andBamHI) cleavage patterns of these nominally 78-MdalC. fascians plasmids suggest that the plasmids are not uniformly of high homology, although similar or identical in electrophoretic mobility in the system used. The relationship of the 78-Mdal plasmids to the phytopathogenicity ofC. fascians remains uncertain, although the restriction endonuclease cleavage patterns do indicate that the plasmids from the highly virulent strains are more closely related to the plasmids from the strains intermediate in virulence than they are to the plasmids from the avirulent strains.     

Proteomic expression profiles of virulent and avirulent strains of Listeria monocytogenes isolated from macrophages

Listeria monocytogenes is able to survive and proliferate within macrophages. In the current study, the ability of three L. monocytogenes strains (serovar 1/2a strain EGDe, serovar 4b strain F2365, and serovar 4a strain HCC23) to proliferate in the murine macrophage cell line J774.1 was analyzed. We found that the avirulent strain HCC23 was able to initiate an infection but could not establish prolonged infection within the macrophages. By contrast, strains EGDe and F2365 proliferated within macrophages for at least 7 h. We further analyzed these strains by comparing their protein expression profiles at 0 h, 3 h, and 5 h post-infection using multidimensional protein identification technology coupled with electrospray ionization tandem mass spectrometry. Our results indicated that similar metabolic and cell wall associated proteins were expressed by all three strains at 3 h post-infection. However, increased expression of stress response and DNA repair proteins was associated with the ability to proliferate in macrophages at 5 h post-infection. By comparing the protein expression patterns of these three L. monocytogenes strains during intracellular growth in macrophages, we were able to detect biological differences that may determine the ability of L. monocytogenes to survive in macrophages.     

Functional macrophage activity in infection with virulent and avirulent strains of the dysentery microbe

The effect of S. flexneri virulent and avirulent (vaccine) strains 2a on the cytoplasmic membrane of mouse macrophages has been studied by evaluating the action of these bacteria on the activity of 5-nucleotidase. The dynamics of the activity of 5-nucleotidase after the introduction of both virulent and avirulent strains has a phasic character with alternating rises and falls in the activity of this enzyme in comparison with the control. S. flexneri vaccine strain produces mainly a stimulating effect on the functional activity of peritoneal macrophages in mice, which is confirmed by a decrease in the activity of 5-nucleotidase; on the contrary, S. flexneri virulent strain- has mainly an inhibiting effect on the functional activity of peritoneal macrophages, which is confirmed by an increase in the activity of 5-nucleotidase in these cells. The comparative study of changes in the activity of 5-nucleotidase, following the introduction of S. flexneri, in mice, previously immunized with smallpox vaccine, and in intact mice has shown that the use of animals immunized with smallpox vaccine in the study of metabolic characteristics may lead to distortions in the results of the experiment.     

Induction of Arabidopsis defense genes by virulent and avirulent Pseudomonas syringae strains and by a cloned avirulence gene.

We developed a model system to study the signal transduction pathways leading to the activation of Arabidopsis thaliana genes involved in the defense against pathogen attack. Here we describe the identification and characterization of virulent and avirulent Pseudomonas syringae strains that elicit disease or resistance symptoms when infiltrated into Arabidopsis leaves. The virulent and avirulent strains were characterized by determining growth of the pathogen in Arabidopsis leaves and by measuring accumulation of mRNA corresponding to Arabidopsis phenylalanine ammonia-lyase (PAL), beta-1,3-glucanase (BG), and chalcone synthase (CHS) genes in infected leaves. The virulent strain, P. syringae pv maculicola ES4326, multiplied 10(5)-fold in Arabidopsis leaves and strongly elicited BG1, BG2, and BG3 mRNA accumulation but had only a modest effect on PAL mRNA accumulation. In contrast, the avirulent strain, P. syringae pv tomato MM1065, multiplied less than 10-fold in leaves and had only a minimal effect on BG1, BG2, and BG3 mRNA accumulation, but it induced PAL mRNA accumulation. No accumulation of CHS mRNA was found with either ES4326 or MM1065. We also describe the cloning of a putative avirulence (avr) gene from the avirulent strain MM1065 that caused the virulent strain ES4326 to grow less well in leaves and to strongly elicit PAL but not BG1 and BG3 mRNA accumulation. These results suggest that the Arabidopsis PAL and BG genes may be activated by distinct signal transduction pathways and show that differences in plant gene induction by virulent and avirulent strains can be attributed to a cloned presumptive avr gene.