Avirulent

Bacterial Macromolecules. I. The Isolation of Deoxyribonucleic Acid from Virulent and Avirulent Strains of Haemophilus pertussis, W. G. Overend, M. Stacey, M. Webb, and J. Ungar, Paper presented at A. G. M., Soc. Gen. Microbiol., April 5, 1950. 

Harman GE, CR Howell, A Viterbo, I Chet, M Lorita (2004) Trichoderma species opportunistic, avirulent plant symbionts. Nat. Revs Microbiol 2 43-56. 

Janssen, R., Bakker, J. and Gommers, F.J. (1990) Selection of virulent and avirulent lines of Gbbodera rostochiensis for the HI resistance gene in Solanum tuberosum ssp. andigena CPC 1673. Review of Nematobgy 13, 265. 

McCormick, B. A., Stocker, B. A., Laux, D. C., and Cohen, P. S. (1988). Roles of motility, chemotaxis, and penetration through and growth in intestinal mucus in the ability of an avirulent strain of Salmonella typhimurium to colonize the large intestine of streptomycin-treated mice. Infect. Immun. 56, 2209-2217. 

Highly resistant wheat varieties exhibit a typical hypersensitive response when infected with an avirulent race of the stem rust fungus. Host cells which are penetrated by a fungal haustorium undergo rapid necrotization, thus depriving the biotrophic parasite of its nutritional basis. 

When radioactive lignin precursors are applied to resistant host plants infected with an avirulent pathogen, the autoradiographic localization of radioactivity in resistant reacting host cells may help to corroborate the participation of lignification in the resistance response. Thorough extraction of non-polymerized precursor with organic solvents and the removal of esterified phenolics by alkaline hydrolysis are important steps in these experiments (25,28,30,31). 

Beardmore et al (30) and Tiburzy (31) showed that epidermal (31) and mesophyll (30,31) cells of resistant wheat plants, penetrated by haus-toria of an avirulent race of the fungus, can be stained with phlorogluci-nol/HCl (31) and chlorine/sulfite (30,31). These cells show yellow autofluorescence under UV-light (30,31), the emission spectrum is identical to that of lignified tracheary elements (31). 

When highly resistant wheat varieties are inoculated with an avirulent race of the stem rust fungus, fungal growth is arrested by the hypersensitive death of the first penetrated host cells (30,31.) Even in very densely inoculated leaves, the reaction of less than one percent of the host cells is sufficient to stop further development of the parasite. This small percentage may be the reason, why no increased content of biochemically determined lignin was measured in infected hypersensitive wheat leaves (60,61). 

The application of two of these inhibitors, N(O-hydroxyphenyl) sulfi-namoyl-tertiobutyl acetate and N(O-aminophenyl) sulfinamoyl-tertiobutyl acetate, to highly resistant wheat leaves infected with an avirulent strain of stem rust resulted in decreased lignification and decreased necrosis of penetrated host cells and concomitantly led to increased fungal development, occasionally even allowing some sporulation to occur (60). 

Biotic Agents. It is well-established that treatment of plants with virulent or avirulent forms of a pathogen, or with a non-pathogen, may induce the formation of fungitoxic compounds (phytoalexins) which prevent or retard subsequent infection by a pathogen. The phytoalexins are formed at the site of inoculation and are not transported to other plant parts. 

Wit, P.J.G.M. de Bakker, J. (1980) Differential Changes in Soluble Tomato Leaf Proteins After Inoculation With Virulent and Avirulent Races of Cladosporium fulvum (syn. Fulvia fulva). Physiological Plant Pathology 17, 121-130. 

Fields, P., Swanson, R., Haidaris, C., Heffron, F. Mutants of Salmonella typhimurium that cannot survive within the macrophage are avirulent. Proc Natl Acad Sci USA 83 (1986) 5189-5193. 

Figure 103 Sad mutants of oats, Avena spp., are deficient in their ability to synthesize anti-microbial saponins and are susceptible to normally avirulent fungi.8,9...

BOTELLA, M. A., PARKER, J. E FROST, L. N BITTNER-EDDY, P. D BEYNON, J. L., DANIELS, M. J., HOLUB, E. B, JONES, J. D. G., Three genes of the Arabidopsis RPP1 complex resistance locus recognize distinct Peronospora parasitica avirulence determinants., Plant Cell., 1998,10, 1847-1860. 

Effects of mammalian sera on avirulent and virulent bacteria were determined by using attenuated (BCG) and virulent (H37Rv) strains of tubercle bacilli and avirulent (strain A) and virulent (strain C) strains of E. coli. All strains were obtained from the culture collection of the Department of Microbiology, Miami University. Bacterial virulence and the infection-promoting effect of iron were determined in Swiss-Webster mice. The degree of virulence of tubercle bacilli for iron-untreated and iron-treated mice has been shown previously (2). In this study, the pathogenicity of E. coli strains was tested by three experiments in which groups of 10 mice were injected intraperitoneally with 5 X 108 cells of strain A and strain C. Mice infected with the strain C died within two days whereas 80-90% of mice inoculated with strain A survived the infection. On the basis of these and several similar experiments (see... 

Table VIII), bacteria of the strain C were designated as virulent and those of strain A as avirulent.

In our further study we investigated effects of various numbers of virulent (strain C) and avirulent (strain A) E. coli on serum microbiostasis. Bovine serum was distributed in 1-ml quantities into small screw-topped tubes and was infected with various numbers of strain A or strain C bacteria. After 12- and 24-hr incubation at 37 °C, samples of infected sera were plated on IPAM. Numbers of bacteria were determined by counting bacterial colonies on plates after 12-hr incubation. Results showed that bovine serum inhibited bacilli of avirulent strain A if the inoculated serum contained less than 12,000 bacilli per 1 ml of serum. Larger inocula of strain A multiplied in serum but at a slower rate than in broth medium (Table III). Bacteria of virulent strain C overcame the iron starvation in bovine serum even when serum was inoculated with as few as 100 cells/ml of serum. The results of this study showed that the rate of bacterial multiplication in bovine serum is determined partly by bacterial numbers in the inoculum. Small inocula of virulent and avirulent bacteria were more inhibited than large inocula. The growth of even minute inocula of virulent bacteria in bovine serum... 

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