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At least 19 recordsLinked to original sources
PubMed1986

Biochemical characterization of a foot-and-mouth disease virus strain attenuated for cattle. Brief report.

Wild-type, virulent (A-24 Cruzeiro subtype) foot-and-mouth disease virus (FMDV), a related attenuated strain and revertants of the attenuated strain were examined by titration on primary bovine kidney (PBK) and baby hamster kidney (BHK-21) cells, as well as, by infection of unweaned mice. Wild type virus grew equally well in all three systems, whereas the attenuated strain had a titer 2-3 log lower in PBK cells than in the other 2 assays. Within 9 successive passages in BHK-21 cells the attenuated strain gave rise to revertants that had regained the growth properties of wild-type virus in PBK cells. After cloning of the attenuated strain by plaque isolations, the same revertant phenotype was obtained within 9 successive passages. Oligonucleotide mapping indicated that the attenuated strain differed from the wild-type and revertants by at least one additional oligonucleotide. Differences in poly(C) length were not found among any of the three strains of FMDV. These results correlate attenuation and virulence with point mutation(s) and not with deletions. Possible reversions in nature with this attenuated strain may be anticipated.

Animals↗
PubMed1985

Homologous interference by a foot-and-mouth disease virus strain attenuated for cattle.

An attenuated strain of foot-and-mouth disease virus (FMDV) of the A24 Cruzeiro subtype grew less well than wild-type virus in primary bovine fetal kidney (PBK) cells resulting in a 4-log lowered efficiency of plaque formation. Both wild-type and attenuated virus grew equally well in baby hamster kidney (BHK) cells and in suckling mice. Using PBK cells, virus-specific RNA of the wild-type accumulated up to 6 hours after infection. In contrast, PBK cells infected with the attenuated strain made less than 20 per cent of the RNA synthesized by wild-type virus. Infection of the cell with wild-type virus followed by superinfection with attenuated virus led to almost complete inhibition of viral RNA synthesis, an effect which is dependent on the concentration of input attenuated virus. Three subsequent undiluted successive passages of the attenuated virus resulted in a preparation which no longer interfered with wild-type RNA synthesis and which induced more of its own viral RNA synthesis in PBK cells. The basis of this interference was considered. Interference occurred intracellularly and was directed only against viruses within the genus FMDV. A role for interferon was ruled out. Attempts to demonstrate the physical presence of defective interfering (DI) particles of FMDV in the attenuated strain failed; but, cyclic patterns of infectivity were produced during successive undiluted passages.

Animals↗
PubMed1987

Technological investigations with attenuated strains of Shigella for production of live vaccines. 1. Cultivation in a fermenter of an attenuated strain S. flexneri 2a with two markers.

A method was developed for cultivation of the strain Shigella flexneri 2a 77 with two attenuated markers. It ensures the preservation of the initial properties of the strain. The regimen for control of dissolved oxygen level was optimized. It was established that yeast extract is a necessary component of the nutritive medium used. The role of the phase and quantity of the inoculum for growth of the bacterial population has been clarified. Fresh fermenter culture, applied in rats, shows a high immunogenic activity. After lyophilization, the cultures retain 50-70% of the immunogenic activity of the non-lyophilized cultures. The method makes preconditions for the production of a live attenuated dysentery vaccine for oral administration.

Animals↗
PubMed1988

Induction of interferon-alpha in human leukocytes by polioviruses: wild-type strains are better inducers than attenuated strains.

Cultures of human peripheral blood leukocytes were exposed to different poliovirus strains at a multiplicity of infection of 1 TCID50/cell. Induction of interferon was a regular phenomenon in the cultures but the maximal yields varied between experiments. Resistance to moderate temperature (56 degrees) and pH 2, as well as antigenic properties, indicated that most of the activity was due to interferon-alpha. Low levels of interferon-gamma were also measured in the cultures using a radioimmunoassay. Using kinetic uv-inactivation we found that infectivity of the virus preparations was affected more rapidly than the capability to induce interferon-alpha. Dependence of interferon-alpha yields on the inducing virus strain was examined in 46 independent cultures by comparing the three serotypes of the attenuated poliovirus vaccine strains and two wild-type strains of serotype 3 (Saukett and P3/FIN/23127/84). The wild-type strains were significantly better inducers of interferon than the attenuated strains (P less than 0.001). Four other wild-type strains representing all serotypes tested in 12 independent cultures were also better interferon inducers than the corresponding Sabin strains (P less than 0.02). Induction of interferon may have a role in the poliovirus-induced inhibition of lymphocyte mitogenesis previously reported by others.

Cells, Cultured↗
PubMed1997

The lag phase rather than the exponential-growth phase on glucose is associated with a higher cAMP level in wild-type and cAPK-attenuated strains of the yeast Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae several phenotypic properties controlled by cAMP-dependent protein kinase (cAPK) are indicative of high cAPK activity during growth on glucose and low activity during growth on non-fermentable carbon sources and in stationary phase. It has been a matter of debate whether the apparently higher activity of cAPK in cells growing on glucose is due to a higher cAMP level or to an alternative mechanism activating cAPK. The cAMP level during diauxic growth of yeast cells in cultures with different initial glucose levels and different initial cell densities has been reinvestigated and the previously reported twofold increase in cAMP during growth initiation has been confirmed. However, this increase was transient and entirely associated with the lag phase of growth. The initiation of exponential growth on glucose was associated with a decrease in the cAMP level and there was no correlation between this decrease in cAMP and the depletion of glucose in the medium. In mutants defective in feedback inhibition of cAMP synthesis, resuspension of exponential-phase glucose-grown cells in glucose medium caused an extended lag phase during which a huge, transient accumulation of cAMP occurred. The latter required the presence of glucose and nitrogen, but not phosphate or sulfate, and was not due to intracellular acidification, as shown by in vivo 31P-NMR spectroscopy. The initiation of exponential growth on glucose was also associated in this case with a decrease in cAMP rather than an increase. This behaviour was also observed in strains with attenuated catalytic subunit activity and lacking the regulatory subunit and even in strains without catalytic subunits of cAPK. This might indicate that other mechanisms are able to cause down-regulation of cAMP synthesis in a way mimicking feedback inhibition. Transfer of glucose-growing cells of wild-type or cAPK-attenuated strains to a nitrogen starvation medium resulted in an increase in the cAMP level rather than a decrease. The results indicate that the apparent changes in cAPK activity in vivo during diauxic growth on glucose and during nitrogen starvation cannot be explained on the basis of changes in the cAMP level.

Cyclic AMP↗
PubMed1986

Immunization studies with attenuated strains of Bacillus anthracis.

Live, attenuated strains of Bacillus anthracis lacking either the capsule plasmid pXO2, the toxin plasmid pXO1, or both were tested for their efficacy as vaccines against intravenous challenge with anthrax toxin in Fischer 344 rats and against aerosol or intramuscular challenge with virulent anthrax spores in Hartley guinea pigs. Animals immunized with toxigenic, nonencapsulated (pXO1+, pXO2-) strains survived toxin and spore challenge and demonstrated postimmunization antibody titers to the three components of anthrax toxin (protective antigen, lethal factor, and edema factor). Immunization with two nontoxigenic, encapsulated (pXO1-, pXO2+), Pasteur vaccine strains neither provided protection nor elicited titers to any of the toxin components. Therefore, to immunize successfully against anthrax toxin or spore challenge, attenuated, live strains of B. anthracis must produce the toxin components specified by the pXO1 plasmid.

Aerosols↗
PubMed1993

Macrophage phagocytosis of virulent but not attenuated strains of Mycobacterium tuberculosis is mediated by mannose receptors in addition to complement receptors.

We have examined macrophage receptors that mediate phagocytosis of virulent strains (Erdman and H37Rv) and an attenuated strain (H37Ra) of the intracellular pathogen, Mycobacterium tuberculosis. Adherence of the three strains to monocyte-derived macrophages (MDM) is markedly enhanced (>threefold) in the presence of low levels of fresh serum and requires heat-labile serum components because heat inactivation of serum reduces adherence by 65 +/- 5 to 71 +/- 2%. In the presence and absence of serum, adherence of the three strains to MDM is comparable. By electron microscopy, all bacteria are ingested and reside in phagosomes. C receptors (CR) play an important role in adherence of the three strains to MDM in the presence and absence of serum. mAb against CR1, CR3, and CR4 inhibit adherence of Erdman M. tuberculosis in fresh serum by 75 +/- 3% and inhibit the low level of adherence of Erdman (71 +/- 13%), H37Rv (72 +/- 1%), and H37Ra (64 +/- 14%) M. tuberculosis in the absence of serum. Mannose receptors (MR) play an important role in mediating macrophage adherence of the virulent strains but not the attenuated strain of M. tuberculosis. Preincubation of MDM with soluble mannan or mannose-BSA consistently and significantly inhibits adherence of Erdman and H37Rv (up to 60 +/- 7%) but not H37Ra (0 +/- 1 to 5 +/- 5% enhancement of adherence) in the absence of serum. Down-modulation of macrophage MR on mannan substrates inhibits adherence of Erdman (52 +/- 8%) and H37Rv (55 +/- 6%) but not H37Ra (2 +/- 2% enhancement of adherence). Preincubation of MDM with soluble N-acetylglucosamine-BSA also significantly inhibits adherence of the virulent strains (42 +/- 3%). Preincubation of MDM with glucose-BSA minimally inhibits adherence of the three strains (2 +/- 4 to 12 +/- 5%). Anti-MR antibody inhibits adherence of Erdman (57 +/- 2%) and H37Rv (44 +/- 4%) but not H37Ra (4 +/- 5% enhancement of adherence). Inhibition of adherence of zymosan was comparable with that seen with virulent strains of M. tuberculosis in these studies. Down-modulation of macrophage MR also inhibits adherence of Erdman (48 +/- 9%) and H37Rv (20 +/- 2%) in the presence of serum. Simultaneous blockade of MR and CR does not further inhibit adherence of the virulent M. tuberculosis strains over that seen with blocking CR alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2005

[Identification of differential genomic genes of Mycobacterium tuberculosis H37Rv and attenuated strain H37Ra by suppression subtractive hybridization].

To study the virulence-related genes in Mycobacterium tuberculosis, we used suppression subtractive hybridization to clone the differential genomic genes between Mycobacterium tuberculosis virulence strain H37Rv and attenuated strain H37Ra. All of 54 different genes were cloned, sequenced and analyzed by Southern-blotting. Two different DNA fragments in H37Ra are new genes so far, and get the new Genbank number AY534505 and AY560011. Eight different DNA fragments in H37Rv were obtained. One is the fragment of a gene coding virulence factor mce; one fragment belongs to the gene coding for purC synthenzyme; one for PE family protein; the other 4 fragments for putative gene; and the last one is a non-coding fragment. PCR analysis indicated that 2 of the different genes were present exclusively in the clinical virulent strain and in H37Rv, but not in the clinical avirulent strain and in H37Ra. The novel differential genes may provide an important clue for studying the mechanism of M. tuberculosis pathogenesis.

DNA, Bacterial↗
PubMed1983

Replication of virulent and attenuated strains of yellow fever virus in human monocytes and macrophage-like cells (U937).

Virulent and attenuated strains of yellow fever virus were compared for their ability to grow in cultures of unstimulated leucocytes and monocytes derived from human peripheral blood, and of a macrophage-like cell line of human origin, U937. The extent of virus growth in leucocyte cultures varied depending on the strain of virus, multiplicity of infection, presence of diluted antibody in the culture medium but independently of the flavivirus immune status of the donor. The same pattern of differential growth was observed in the three types of cultures used. Although strain related variation in growth occurred within both virulent and attenuated strains, most of the attenuated strains produced higher virus yields than the virulent ones, suggesting that replication in this cell system is not related to the expression of virulence for the host. Replication in human monocytes as an in vitro marker of immunogenity for substrains of 17 D vaccine virus is discussed.

Adult↗
PubMedDate not supplied

[Criteria of primary screening of attenuated strains for live vaccine against Influenza A].

Reassortant strains for live influenza vaccine (LIV) were selected using two additional markers: intensity of cytopathic effect (CPE) at 40 degrees C in MDCK cells and toxicity for mice (induction of acute hemorrhagic pulmonary edema after intranasal challenge with undiluted virus). All wild-type viruses induced a high CPE in MDCK cells, while the reassortants differed by this sign. Only vaccine strains and attenuation donors were characterized by a low CPE. Modern epidemic viruses are highly toxic for mice, causing the death of 60-100% animals from hemorrhagic pulmonary edema on days 3-4 after intranasal infection. Attenuation donors and vaccine strains were not toxic for mice, the level of toxic effect correlating with CPE in MDCK culture. Evaluation of CPE in MDCK culture and toxicity for mice can be used for primary screening of candidates for LIV.

Animals↗
PubMed1987

Attenuated strains of tobacco mosaic virus. Reduced synthesis of a viral protein with a cell-to-cell movement function.

Attenuated strains of tobacco mosaic virus (TMV) have been used to protect crops against virulent strains. The synthesis of viral proteins and RNAs was investigated in protoplasts that had been infected separately with three tomato strains of TMV, virulent type L, and attenuated strains L11 and L11A. It was revealed that the mutations, which are responsible for the viral attenuation and have been mapped in the p126 (p184) gene, caused a reduction of the synthesis of the viral-coded p30 protein with a cell-to-cell movement function and its mRNA, but it had no significant effect on the synthesis of other viral proteins and RNAs in virus-infected protoplasts. Thus, it was shown that the attenuated strains can multiply as efficiently as the virulent strain in initially inoculated cells, but they can not spread efficiently outside the infected cells. In addition, it is suggested that a non-structural protein, p126 or p184, of TMV is involved in the synthesis of viral subgenomic p30 mRNA.

Mutation↗
PubMed1999

Immune response to rotavirus VP4 expressed in an attenuated strain of Shigella flexneri.

An attenuated strain of Shigella flexneri was utilised to express viral protein (VP) 4 of rotavirus and the immunogenicity of the recombinant constructs was studied in BALB/c mice. VP4 was expressed as a fusion with maltose binding protein (MBP) in both the cytoplasm and periplasm, with a much higher level of expression occurring in the former. While all constructs induced a Shigella-specific response in mice, only the construct expressing MBP-VP4 in the cytoplasm of Shigella stimulated an immune response specific to rotavirus. This study demonstrates that Shigella can be used to deliver rotavirus antigens and induces an immune response directed towards both rotavirus and Shigella.

Animals↗
PubMed1980

Herpesvirus saimiri: protective effect of attenuated strain against lymphoma induction.

An attenuated strain of Herpesvirus saimiri (A-HVS) induced a persistent, latent infection in common marmosets. Virus was recovered from circulating lymphocytes of infected animals and antibody response to virus-specified antigens was demonstrated over 3-12 months PI. A-HVS-infected common marmosets and animals without previous A-HVS exposure were challenged with oncogenic HVS (125-825 PFU); marmosets without A-HVS infection developed malignant lymphoproliferative disease and died 3 weeks PI whereas all persistently-infected animals have survived 38-43 months post challenge.

Animals↗
PubMed1984

A wild and an attenuated strain of Francisella tularensis differ in susceptibility to hypochlorous acid: a possible explanation of their different handling by polymorphonuclear leukocytes.

We have previously reported that a wild strain of Francisella tularensis is much less efficiently killed by human polymorphonuclear leukocytes than is an attenuated strain. In the present study, the killing of the attenuated strain was found to be strictly oxygen dependent. The wild and the attenuated strains both induced a respiratory burst in the leukocytes. The difference between the strains in susceptibility to agents produced at the burst could be explained by a difference in susceptibility to hypochlorous acid.

Francisella tularensis↗