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At least 19 recordsLinked to original sources

PubMed1994

Virulence and pathogenesis of non-virulent and virulent strains of pseudorabies virus expressing envelope glycoprotein E1 of hog cholera virus.

Pseudorabies virus (PRV) expressing the envelope glycoprotein E1 (E1) of hog cholera virus (HCV) was used as a model to study the potential risks connected with the use of a live herpesvirus vaccine expressing a foreign gene. The gene encoding E1 was inserted into the glycoprotein X (gX) locus of both a virulent PRV strain and a non-virulent PRV strain in which the virulence genes encoding glycoprotein I (gI) and thymidine kinase (TK) had been inactivated. We investigated whether strain M205 (gI-, TK-, gX-, E1+) had a changed cell or host tropism or virulence compared with strain M206 (gI-, TK-, gX-) in pigs, rabbits, hamsters, rats, mice and rhesus monkeys. The insertion of E1 into this non-virulent PRV strain caused no change in cell or host tropism. However, pigs inoculated with M205 shed less virus over a shorter period than pigs inoculated with M206. Theoretically, virulent PRV strains expressing E1 (gX-, E1+) could arise through transfer of the E1 gene of M205 to a virulent PRV strain. Therefore, we inoculated pigs with strain M12 (gX-, E1+) or the control strain M104 (gX-) and compared the virulence and pathogenesis. M12 and M104 were of approximately equal virulence and the pathogenesis of both strains was similar. We concluded that incorporating E1 of HCV into the gX locus of PRV did not change cell or host tropism, nor did it change the virulence of either non-virulent or virulent PRV.

Animals↗

PubMed2003

Effect of fusion protein cleavage site mutations on virulence of Newcastle disease virus: non-virulent cleavage site mutants revert to virulence after one passage in chicken brain.

Virulence of Newcastle disease virus (NDV) is mainly determined by the amino acid sequence of the fusion (F0) protein cleavage site. Full-length NDV cDNA clone pNDFL was used to generate infectious NDV with defined mutations in the F0 cleavage site (RRQRR downward arrow L, GRQGR downward arrow F, RRQGR downward arrow F, RGQRR downward arrow F and RKQKR downward arrow F). All the mutants were viable and the mutations were maintained after virus propagation in embryonated eggs. The mutants showed single-cell infections on chicken embryo fibroblasts, which suggested that they were non-virulent. However, virulence tests in 1-day-old chickens resulted in an intracerebral pathogenicity index (ICPI) between 0 and 1.3. Moreover, virulent virus was isolated from chickens that had died in the virulence tests. Subsequent sequence analysis showed that the mutants RRQRR downward arrow L, RRQGR downward arrow F, RGQRR downward arrow F and RKQKR downward arrow F gave rise to the appearance of revertants containing the virulent cleavage site RRQ(K/R)R downward arrow F and an ICPI of 1.4 or higher. This indicated that reversion to virulence was caused by alteration of the amino acid sequence of the F0 cleavage site from a non-virulent to a virulent type. Furthermore, the ICPI of the revertants was higher than that of cDNA-derived strain NDFLtag, which has the same cleavage site, RRQRR downward arrow F (ICPI=1.3). NDFLtag(Pass), which was isolated from dead chickens after intracerebral inoculation of NDFLtag, also showed an increase in the ICPI from 1.3 to 1.5. This study proves that reversion to virulence occurs within non-virulent NDV populations and that the virulence may increase after one passage in chicken brain.

Animals↗

PubMed2000

[Evaluation of the usefulness of selected virulence markers for identification of virulent strains of Yersinia enterocolitica strains. III. Chromosome markers of virulence].

It is well known that virulent strains of Y. enterocolitica bear the virulence-associated plasmid pYV. Moreover some authors consider that the pathogenic strains of these bacteria have chromosome encoded phenotypic and genotypic features such as: genes ail and yst which could be used as virulence markers. The virulent strains of Y. enterocolitica do not produce pyrasinamidase and are not able to ferment salicin and cannot hydrolyse esculin. In addition these strains produce thermostable enterotoxin called YST and protein Ail (attachment invasion locus). In contrast to phenotypic virulence makers the biological function of proteins Ail, YST and nucleotide sequence of genes ail and yst is well described. In the presented study one hundred thirty virulence plasmid bearing Y. enterocolitica strains belonging to serogroup O3 were examined for the presence of genes ail, yst, and were tested for their inability to pyrasinamidase production, salicin fermentation and esculin hydrolysis. In addition forty pYV plasmid-cured isogenic strains were included in to the study. Genes ail and yst were detected by polymerase chain reaction (PCR). The obtained results indicate that all tested 130 pYV+ Y. enterocolitica strains as well as 40 plasmid-cured isogenic strains have carried ail and yst genes. All tested strains did not produce pyrasinamidase, hydrolyse esculin and ferment salicin. This generally was in agreement with the observations done by other authors and suggest that the chromosomal virulence markers, especially well described genes ail and yst, could be useful for excluding the potential virulence of Y. enterocolitica strains, which had lost pYV plasmid and have no ail or yst genes. Therefore, in clinical studies, Y. enterocolitica strains isolated directly from patients should be primarily tested for the presence of the virulence plasmid and secondarily, the negative ones could be examined for the presence of the chromosomal virulence markers.

Bacterial Outer Membrane Proteins↗

PubMed2002

Growth characteristics of a highly virulent, a moderately virulent, and an avirulent strain of equine arteritis virus in primary equine endothelial cells are predictive of their virulence to horses.

Equine viral arteritis (EVA) is an endotheliotropic viral disease of horses caused by equine arteritis virus (EAV). Although there is only one serotype of EAV, there is marked variation in the virulence of different strains of the virus. The replication and cytopathogenicity of three well-characterized strains of EAV of different virulence to horses were compared in rabbit kidney (RK-13) and primary equine pulmonary artery endothelial cells (ECs). Viral protein expression, plaque size, and cytopathogenicity of all three viruses were similar in RK-13 cells, whereas two virulent strains of EAV were readily distinguished from an avirulent strain by their plaque morphology and cytopathogenicity in primary equine ECs. Furthermore, EAV nucleocapsid protein was detected by flow cytometric analysis significantly later in ECs infected with the avirulent than those infected with the virulent strains of EAV. Primary equine ECs provide a convenient and relevant model for in vitro characterization of the pathogenesis of EVA and the virulence determinants of EAV.

Animals↗

PubMed2004

Differences in the carriage and the ability to utilize the serotype associated virulence plasmid in strains of Salmonella enterica serotype Typhimurium investigated by use of a self-transferable virulence plasmid, pOG669.

Most strains of Salmonella enterica subspecies enterica serotype typhimurium (S. typhimurium) naturally harbour a virulence plasmid which carries the salmonella plasmid virulence (spv) genes. However, isolates belonging to certain phage types are generally found without the plasmid. We have utilized a self-transferable virulence plasmid, pOG669 to investigate the effect of introduction of spv genes into strains of such phage types. The use of the co-integrate plasmid, pOG669, was validated on a diverse collection of strains. pOG669 was transferred into strains of serotypes that are normally associated with the possession of virulence plasmids. All strains maintained the wild type level of virulence in a mouse model, except that introduction of pOG669 restored normal virulence levels in an avirulent, plasmid free strain of S. dublin and resulted in a decrease in virulence in a strain of S. dublin from clonal line Du3. S. gallinarum did not become virulent in mice, but pOG669 was functionally interchangeable with the wild type plasmid when strains were tested in a chicken model. Strains of serotypes not normally associated with the carriage of a virulence plasmid did not increase in virulence upon the introduction of pOG669. An IncX plasmid pOG670 that was included as control was incompatible with the virulence plasmid in a strain of S. dublin, demonstrating that the common virulence plasmid of this serotype is of a different incompatibility group than other virulence plasmids. Strains of S. typhimurium from phage types that do not normally carry a virulence plasmid responded differently to attempts to introduce pOG669. No transconjugants were observed with the strains of DT5 and DT21. The introduction of pOG669 did not alter the virulence of JEO3942(DT10), DT35 and JEO3949(DT66) significantly, while DT1 and DT27 became more virulent. DT27 became as virulent as wild type C5, while logVC(10) of DT1 only increased from 4.1 to 5.7. The ability to express spv-genes was measured by use of an spvRAB'-cat fusion. Expression in S. enteritidis was found to be higher than in other serotypes tested. Only serotypes that naturally carry a virulence plasmid expressed spv-genes. The strain of DT1 expressed spv at a very low level, while expression in the strains of DT10 and DT35 was approximately 2-fold lower than in a control strain of S. typhimurium, while the level in the DT66 strain corresponded to the control strain. The plasmid pSTF9, which carried the fusion gene could not be introduced into the strains of DT5, DT21 and DT27. The RpoS level in the strains was measured indirectly by use of a katE-lacZ fusion. In the DT5 strain the level of expression was low, while the strains JEO3942(DT10), DT21, DT27 and DT35 expressed 4-5 fold the level in this strain. An internal fragment of the rpoS gene was sequenced in three strains. These all showed an identical sequence to a published S. typhimurium rpoS gene.

Animals↗

PubMed1997

Virulence plasmid instability in Shigella flexneri 2a is induced by virulence gene expression.

Expression of the predominantly plasmid-encoded virulence regulon of Shigella flexneri 2a is induced by growth at 37 degrees C and repressed by growth at 30 degrees C. During growth at 37 degrees C, spontaneous S. flexneri mutants arise which have undergone virulence plasmid curing or rearrangement and no longer display the virulent phenotype. In the laboratory, the unstable nature of the virulence plasmid causes complete loss of virulence in a growing population. We have undertaken an analysis of virulence plasmid instability, classifying events which produced individual avirulent derivatives within a virulent population and identifying the factor(s) which controlled conversion. Multiplex PCR analysis of DNA obtained from spontaneous avirulent derivatives indicated that virF and virB were deleted or otherwise inactivated in over 97% of the isolates. The virF and virB loci encode regulatory proteins required for transcriptional activation of the virulence regulon. Inactivation of these key regulatory loci in the vast majority of avirulent derivatives which arose during growth at 37 degrees C suggested that virulence gene expression induced virulence plasmid instability. Consistent with this hypothesis, we observed stable virulence plasmid maintenance during growth of a wild-type strain at 30 degrees C where virulence gene expression was repressed. The virulence plasmid was also stably maintained in virF and virB mutants grown at 37 degrees C. Conversely, virulence plasmid destabilization was induced at 30 degrees C and accelerated at 37 degrees C through expression of VirF or VirB from multicopy plasmids. These results indicate that exposure of S. flexneri to conditions favoring induction of the virulent phenotype also favor its loss. The significance of this paradox of Shigella pathogenicity is discussed.

Bacterial Proteins↗

PubMed1998

Tissue culture assays using Caco-2 cell line differentiate virulent from non-virulent Listeria monocytogenes strains.

Within the group of Listeria sp., only L. monocytogenes is pathogenic for humans and numerous studies of L. monocytogenes strains have described non-virulent isolates. In this study, the potential value of two tissue culture assays (TCA) was analysed to ascertain the virulence properties of L. monocytogenes strains, initially typed for virulence using the immunocompromised mouse model (ICMM). The first assay assessed both the penetration into, and multiplication within, Caco-2 cells (PM assay): the second was a plaque-forming assay (PF assay). All the clinical isolates (nine strains) were virulent in both TCA. Conversely, all the non-pathogenic species (seven strains) were non-virulent in PM and PF assays. Compared with the virulence obtained in the ICMM with 29 Listeria strains, including 12 non-virulent L. monocytogenes strains, the sensitivity of both TCA was equal to1. Specificity was 0.89 and 0.84 for the PF and PM assays, respectively. However, a study of strains exhibiting virulence differences in three other in vivo virulence models showed that ICMM only detected highly virulent strains. The specificity of the PF test could, therefore, be higher, and close to that obtained by the enumeration of viable bacteria in the spleen of mice infected by subcutaneous injection in the footpad and by intravenous injection. Taken together, this study confirms the existence of low-virulence L. monocytogenes strains and shows that the virulence status of some non-clinical L. monocytogenes isolates depends on the virulence models used. The data suggest that the PF assay could be used as a primary test to evaluate the virulence of Listeria strains in order to reduce the cost of testing all strains in vivo.

Animals↗

PubMed1999

Tumour necrosis factor and interferon-gamma are required in host resistance against virulent Rhodococcus equi infection in mice: cytokine production depends on the virulence levels of R. equi.

Rhodococcus equi is a facultative intracellular bacterial pathogen that causes pneumonia in foals and immunosuppressed humans. There are at least three virulence levels of R. equi and these pathogenicities are associated, in mice, with the presence of virulence plasmids. This study focused on cytokine secretion, in mice, in the course of a primary infection with sublethal doses of R. equi strains of different virulence levels (virulent, intermediately virulent and avirulent). Tumour necrosis factor (TNF) and interferon-gamma (IFN-gamma), but not interleukin-4 (IL-4) and interleukin-10 (IL-10), were induced endogenously in mice in relation to the multiplication and clearance of virulent and intermediately virulent strains of R. equi. These cytokines were not detected in mice infected with avirulent R. equi. Deaths occurred among mice treated with monoclonal antibodies (mAbs) against either TNF or IFN-gamma prior to sublethal dose infection with virulent and intermediately virulent strains of R. equi, but not with avirulent R. equi. These results suggested that cytokine production depended largely on the virulence levels of R. equi: TNF and IFN-gamma were required early during infection with virulent R. equi to limit replication and clearance of bacteria within the organs, but they were not necessary for limiting infection with avirulent R. equi.

Actinomycetales Infections↗

PubMed1992

Identification, genetic analysis and DNA sequence of a 7.8-kb virulence region of the Salmonella typhimurium virulence plasmid.

The 90-kilobase (kb) virulence plasmid of Salmonella typhimurium is responsible for invasion from the intestines to mesenteric lymph nodes and spleens of orally inoculated mice. We used Tn5 and aminoglycoside phosphotransferase (aph) gene insertion mutagenesis and deletion mutagenesis of a previously identified 14-kb virulence region to reduce this virulence region to 7.8kb. The 7.8-kb virulence region subcloned into a low copy-number vector conferred a wild-type level of splenic infection to virulence plasmid-cured S. typhimurium and conferred essentially a wild-type oral LD50. Insertion mutagenesis identified five loci essential for virulence, and DNA sequence analysis of the virulence region identified six open reading frames. Expected protein products were identified from four of the six genes, with three of the proteins identified as doublet bands in Escherichia coli minicells. Three of the five mutated genes were able to be complemented by clones containing only the corresponding wild-type gene. Only one of the five deduced amino acid sequences, that of the positive regulatory element, SpvR, possessed significant homology to other proteins. The codon usage for the virulence genes showed no codon bias, which is consistent with the low levels of expression observed for the corresponding proteins. Consensus promoters for several different sigma factors were identified upstream of several of the genes, whereas only consensus Rho-dependent termination sequences were observed between certain of the genes. The operon structure of this virulence region therefore appears to be complex. The construction of the cloned 7.8-kb virulence region and the determination of the DNA sequence will aid in the further genetic analysis of the five plasmid-encoded virulence genes of S. typhimurium.

Amino Acid Sequence↗

PubMed2004

The effect of mutation on Rhodococcus equi virulence plasmid gene expression and mouse virulence.

An 81 kb virulence plasmid containing a pathogenicity island (PI) plays a crucial role in the pathogenesis of Rhodococcus equi pneumonia in foals but its specific function in virulence and regulation of plasmid-encoded virulence genes is unclear. Using a LacZ selection marker developed for R. equi in this study, in combination with an apramycin resistance gene, an efficient two-stage homologous recombination targeted gene mutation procedure was used to mutate three virulence plasmid genes, a LysR regulatory gene homologue (ORF4), a ResD-like two-component response regulator homologue (ORF8), and a gene (ORF10) of unknown function that is highly expressed by R. equi inside macrophages, as well as the chromosomal gene operon, phoPR. Virulence testing by liver clearance after intravenous injection in mice showed that the ORF4 and ORF8 mutants were fully attenuated, that the phoPR mutant was hypervirulent, and that virulence of the ORF10 mutant remained unchanged. A virulence plasmid DNA microarray was used to compare the plasmid gene expression profile of each of the four gene-targeted mutants against the parental R. equi strain. Changes were limited to PI genes and gene induction was observed for all mutants, suggesting that expression of virulence plasmid genes is dominated by a negative regulatory network. The finding of attenuation of ORF4 and ORF8 mutants despite enhanced transcription of vapA suggests that factors other than VapA are important for full expression of virulence. ORF1, a putative Lsr antigen gene, was strongly and similarly induced in all mutants, implying a common regulatory pathway affecting this gene for all four mutated genes. ORF8 is apparently the centre of this common pathway. Two distinct highly correlated gene induction patterns were observed, that of the ORF4 and ORF8 mutants, and that of the ORF10 and phoPR mutants. The gene induction pattern distinguishing these two groups paralleled their virulence in mice.

Actinomycetales Infections↗

PubMed1985

Virulence of Staphylococcus aureus in a mouse mastitis model: studies of alpha hemolysin, coagulase, and protein A as possible virulence determinants with protoplast fusion and gene cloning.

Mutants of a genetically well-characterized strain of Staphylococcus aureus [SA113(83A)] were isolated after mutagenization. Alpha-hemolysin- (hla), coagulase- (coa), and protein A- (spa) negative mutants were characterized by more than 90 biochemical tests for production of extracellular proteins and biochemical profile to exclude pleiotropy. Protoplast fusion was then used to isolate double-defective (hla and coa) recombinants and recombinants with regained properties, i.e., production of alpha-hemolysin and coagulase. Studies of such mutants and recombinants in the mouse mastitis model showed that one alpha-hemolysin [SA113(83A) hla-5] and one coagulase-negative [SA113(83A) coa-147] mutant were lower in virulence compared with the wild-type strain SA113(83A). The double-negative mutant SA113(83A) hla-5 coa-147 showed a drastic decline in virulence and only induced very mild changes, as determined by microscopic examinations of infected mammary gland tissue. The recombinant with regained properties, however, was as virulent as the wild-type strain. This suggests that alpha-hemolysin and coagulase are virulence determinants of S. aureus. A high-level protein A-producing mutant (U300) showed the same virulence as the parent strain SA113(83A) in this model. One low virulence protein A-negative mutant (U320) did not markedly increase in virulence when a plasmid containing the cloned gene for protein A (pSPA15) was introduced into this mutant. By these and earlier observations, it seems likely that protein A is not an important virulence determinant in mastitis of mice. The reduced virulence of the protein A-negative mutant U320 compared with the wild-type SA113(83A) may be due to pleiotropic loss of some other unknown virulence determinant(s). Our data confirm earlier findings that pleiotropic changes are common in protein A-negative mutants.

Animals↗

PubMed2001

Prevalence of virulent Rhodococcus equi in soil from five R. equi-endemic horse-breeding farms and restriction fragment length polymorphisms of virulence plasmids in isolates from soil and infected foals in Texas.

Rhodococcus equi isolates (462) obtained from 64 soil samples collected on 5 R. equi-endemic horse-breeding farms and isolates from 100 infected foals in Texas were examined to determine the prevalence and genotypic diversity of virulence-associated plasmids. Isolates were tested for the presence of 15-17-kDa virulence-associated protein antigens (VapA) by immunoblotting and virulence-associated plasmids by PCR. Plasmid DNAs were isolated and analyzed by digestion with restriction endonucleases for estimation of size and comparison of polymorphisims. Rhodococcus equi were isolated from soil of all 5 farms; however, virulent R. equi were only isolated from 3 of the 5 farms and represented 18.8% (87 of 462) of total isolates. Of the 87 virulent soil isolates, 56 (64.5%) contained an 85-kb type I plasmid, 23 (26.4%) an 87-kb type I plasmid, 7 (8%) a newly defined 85-kb type III plasmid (Tx 43), and 1 (1.1%) a newly defined 85-kb type IV plasmid (Tx 47). Of the 100 isolates from infected foals, 96 were virulent. Of the 96 virulent isolates, 51 (53.1%) contained an 85-kb type I plasmid, 39 (40.6%) an 87-kb type I plasmid, 4 (4.2%) an 85-kb type III plasmid (Tx 43), and 2 (2.1%) an 85-kb type IV plasmid (Tx 47). There are at least 4 different R. equi virulence-associated plasmids in Texas, 2 of which have not previously been described. Based upon virulence plasmid typing, there is geographic diversity among isolates of R. equi from clinical and environmental samples on horse-breeding farms in Texas. There is not a strong correlation between the presence of virulent R. equi in farm soils and the R. equi disease status of those farms.

Actinomycetales Infections↗

PubMed2003

Putrescine or a combination of methionine and arginine restores virulence gene expression in a tRNA modification-deficient mutant of Shigella flexneri: a possible role in adaptation of virulence.

The wild-type strain YSH6000 of Shigella flexneri growing in minimal medium contains the modified nucleoside epoxy-Q (oQ) in a subset of tRNAs. This nucleoside is lacking in tRNA from a tgt mutant of this bacterium. When these bacteria are growing in minimal medium, the expression of virulence genes is 10-fold lower in the tgt mutant than in the wild type, although only a twofold reduction in the expression of these virulence factors is observed in broth. Such a strong media-dependant expression of virulence genes was not observed in the wild type. Accordingly, the level of the positive regulator of virulence, VirF, is much lower in the mutant than in the wild type. However, the transcription of the virF gene in minimal medium is the same in the wild type and in the tgt mutant. As the undermodification of tRNA is not affected by the quality of the growth medium, we conclude that such an environmental change in growth conditions partly restores virulence gene expression by counteracting poor translation of the virF mRNA mediated by an oQ-deficient tRNA. Virulence gene expression is partly restored in the tgt mutant by the addition of a mixture of arginine and methionine. Addition of the polyamine putrescine, synthesis of which is metabolically related to that of arginine and methionine, has a comparable stimulatory effect on virulence gene expression. These results not only suggest a role for amino acids and polyamines in the environmental regulation of virulence gene expression in S. flexneri, but also demonstrate a strong and specific involvement of tRNA modifications, and especially oQ, in the adaptation of virulence gene expression to the nutritional quality of the growth medium.

Adaptation, Physiological↗

PubMed2003

PCR detection of virulence genes in Yersinia enterocolitica and Yersinia pseudotuberculosis and investigation of virulence gene distribution.

PCR-based assays were developed for the detection of plasmid- and chromosome-borne virulence genes in Yersinia enterocolitica and Yersinia pseudotuberculosis, to investigate the distribution of these genes in isolates from various sources. The results of PCR genotyping, based on 5 virulence-associated genes of 140 strains of Y. enterocolitica, were compared to phenotypic tests, such as biotyping and serotyping, and to virulence plasmid-associated properties such as calcium-dependent growth at 37 degrees C and Congo red uptake. The specificity of the PCR results was validated by hybridization. Genotyping data correlated well with biotype data, and most biotypes resulted in (nearly) homogeneous genotypes for the chromosomal virulence genes (ystA, ystB, and ail); however, plasmid-borne genes (yadA and virF) were detected with variable efficiency, due to heterogeneity within the bacterial population for the presence of the virulence plasmid. Of the virulence genes, only ystB was present in biotype 1A; however, within this biotype, pathogenic and apathogenic isolates could not be distinguished based on the detection of virulence genes. Forty Y. pseudotuberculosis isolates were tested by PCR for the presence of inv, yadA, and lcrF. All isolates were inv positive, and 88% of the isolates contained the virulence plasmid genes yadA and lcrF. In conclusion, this study shows that genotyping of Yersinia spp., based on both chromosome- and plasmid-borne virulence genes, is feasible and informative and can provide a rapid and reliable genotypic characterization of field isolates.

Animals↗

PubMed1953

Studies on the virulence of tubercle bacilli; variations in virulence effected by tween 80 and thiosemicarbazone.

Tubercle bacilli were grown in the presence of different concentrations of tween 80, ranging from 0.05 to 2.1 per cent. Equal numbers of viable bacteria from these cultures were compared in infection experiments in the mouse. The average survival time of the mice was used as a criterion for the virulence of the bacilli. High tween concentrations in the culture medium caused a reduction of the bacterial virulence. The reduction was slight in bacterial suspensions from cultures with tween 80 ranging from 0.05 to 1.0 per cent, but considerable in cultures with 2.1 per cent tween. Bacteria grown in the presence of 2.1 per cent tween gave rise to the same number of colonies, in vitro, as bacteria grown in ordinary media. Their oxygen uptake was increased as compared with that of bacilli grown in media containing less tween. Virulent bacteria grown in the presence of high amounts of tween 80 decolorized methylene blue in a test in which organisms from the same virulent strain but cultured without tween, or with only small proportions of the detergent in the medium, did not reduce the dye. A positive methylene blue test is typical of non-virulent tubercle bacilli and of saprophytic mycobacteria. Essentially the same changes occurred when virulent tubercle bacilli were grown in the presence of 0.5 microg./ml. of para-formacetanilide thiosemicarbazone (TBI). This small amount of the substance was not sufficient to prevent the growth of bacteria, or to reduce the number of viable cells in a culture, but it reduced the virulence of the bacteria considerably and rendered them capable of decolorizing methylene blue. Cord factor, a lipid constituent of virulent bacteria which is toxic for mice, was shown to be present in filtrates from cultures of virulent bacteria when the media contained 2 per cent tween 80, but no such material could be recovered from culture filtrates containing the usual 0.05 per cent tween. On the other hand, no toxic material could be extracted from bacteria grown in the presence of 0.5 microg./ml. TBI.

Animals↗

PubMed1984

Loss of pigmentation in Shigella flexneri 2a is correlated with loss of virulence and virulence-associated plasmid.

In this study, we examined the relationship between the virulence of Shigella flexneri 2a and the ability of strains of S. flexneri 2a to absorb Congo red. Spontaneous nonpigmented (i.e., unable to bind Congo red [Pcr-]) derivatives of a virulent, pigmented (Pcr+) strain of S. flexneri 2a were isolated and assayed for virulence as determined by their ability to invade epithelial cells. All Pcr- mutants examined lost the ability to invade epithelial cells and were thus avirulent. Agarose gel electrophoresis of plasmid DNA from these avirulent, Pcr- mutants showed that the majority of these strains had lost a plasmid band corresponding to a virulence-associated plasmid, pSf2a140. In many of the mutants, concomitant loss of pigmentation, virulence, and pSf2a140 was accompanied by the appearance of a new plasmid, smaller than pSf2a140. We believe these new plasmids to be deletion derivatives of pSf2a140 and that loss of pigmentation and loss of virulence are associated with deletions in pSf2a140. We transduced Pcr- mutants to Pcr+ and isolated transductants which suppressed the Pcr- phenotype. None of the Pcr+ transductants regained the ability to invade epithelial cells. Several suppressors of the Pcr- phenotype were identified as mutations in cell wall biosynthesis. These results support our belief that although pigmentation is usually associated with virulence, genetic determinants unrelated to virulence can also affect the ability of the cell to bind Congo red. Therefore, the ability of S. flexneri 2a to bind Congo red does not necessarily imply the ability to invade epithelial cells. However, loss of ability to bind Congo red is accompanied by loss of virulence.

Cell Line↗

PubMed1993

Variation in rotavirus virulence: a comparison of pathogenesis in calves between two rotaviruses of different virulence.

Variation in virulence between two bovine rotaviruses was investigated using ten female and ten male 10-day-old gnotobiotic calves of five breeds or cross breeds that were inoculated with a virulent strain or a strain of low virulence. Similar numbers of infectious viral particles were detected in feces of calves inoculated with either virus, but diarrhea, xylose malabsorption, and reduction of villus height occurred only after inoculation with virulent virus. The mean percentage of the area of the villus epithelium per villus immunostained for rotavirus antigen was eight times greater in calves inoculated with virulent virus, and the mean percentage of villi on which immunostained enterocytes were detected was twice as large in calves inoculated with virulent virus than in calves inoculated with the virus of low virulence. Mean crypt death and mean crypt cell production rates were increased after inoculation with either virus. Virulence was associated with extensive spread of infection through the small intestine, preferential colonization of the proximal small intestine, and marked damage to enterocytes and villi. The virus of low virulence infected the proximal small intestine poorly, and although it infected more enterocytes in the mid and distal small intestine and replicated in them, causing cytopathic effects, it did not damage intestinal structure and affect function.

Animals↗

PubMed2000

[Evaluation of the usefulness of selected virulence markers for the identification of virulent Yersinia enterocolitica strains. I. Phenotypic markders associated with Plasmid pYV].

The species Yersinia enterocolitica includes either pathogenic or non-pathogenic strains. Therefore it is necessary to differentiate virulent bacilli from other. It is well known that pathogenic strains of Y. enterocolitica bearing virulence associated plasmid called pYV, which could be demonstrated by its isolation or detected by the presence of specific, phenotypic properties directly related with this plasmid. The aim of the presented paper was to check the ability of some phenotypic virulence markers associated with pYV, to detection of pathogenic Y. enterocolitica strains. In the presented work 152 (130 carrying pYV) clinical strains of Y. enterocolitica O3 isolated mainly from stool were examined for the presence of phenotypic virulence markers such as: calcium dependency, Congo-red binding, autoagglutination and agglutination with Mangifera indica extract. Both first features were detected parallel, on the same plate, using CRMOX (Congo-red, Magnesium Oxalate) agar. The detection of the tested markers in the examined strains was compared with the presence of virulence plasmid. The obtained results confirmed the observations done by other authors that Y. enterocolitica strains, in which bacilli bearing the virulence plasmid predominate, exhibit all tested phenotypic properties whereas the plasmid-cured isogenic strains show no one of these features. Therefore all the tested markers could be useful for detection of virulent Y. enterocolitica strains directly isolated from patients. The most useful virulence markers in bacteriological study seems to be calcium dependency and Congo-red binding, examined together by the use of CRMOX agar, because they confirm the presence of the virulence plasmid by parallel detection of two physiologically different features associated with this plasmid. In addition CRMOX agar allows for the examination rough strains while agglutination tests do not.

Bacterial Proteins↗