An evaluation of the ELISA technique was made in order to obtain a very specific and sensitive method for strain identification of Rhizobium meliloti. Antisera against an R. meliloti strain were produced by using as antigen either whole cells or purified lipopolysaccharides from the cell wall. The use of whole cells as antigen gave rise to antibodies which were more sensitive and strain specific than those produced from purified lipopolysaccharides. A further evaluation of the ELISA method was the use of a new type of conjugate consisting of a purified antibody linked to β-galactosidase by using as coupling reagent a hetero-bifunctional reagent, N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP), which contains two reactive groups directed towards different functional groups. Substrate for this type of conjugate consisted of o-nitrophenyl-β-D-galactopyranoside. This improved technique makes it possible to detect bacteria in samples containing 1 × 103 cells ml−1 whilst retaining strain specificity. Furthermore, preparations of nodules formed by different R. meliloti strains containing 1 × 105 cells ml−1 could be analysed whilst retaining strain specificity. The technique presented thus offers advantages in higher sensitivity and reliability than conventional ELISA techniques.
BergerJ. A.,
MayS. N.,
BergerL. R.,
BohloolB. B.1979; Colorimetric enzyme-linked immunosorbent assay for the identification of strains ofRhizobium in culture and in the nodules of lentil. Applied and Environmental Microbiology 37:642–646
BishopP. E.,
GuevaraJ. G.,
EngelkeJ. A.,
EvansH. J.1976; Relation between glutamine synthetase and nitrogenase activities in the symbiotic association betweenRhizobium japonicum andGlycine max.
. Plant Physiology 57:542–546
CarlssonJ.,
DrevinH.,
AxenR.1978; Protein thiolation and reversible protein-protein conjugation. N-Succinimidyl-3-(2-pyridyldithio)propionate, a new heterobifunctional reagent. Biochemical Journal 173:723–737
ClarkM. F.,
AdamsA. N.1977; Characteristics of the microplate methods of enzyme-linked immunosorbent assay for the detection of plant viruses. Journal of General Virology 34:475–483
EngvallE.,
PerlmannP.1972; Quantitation of specific antibodies by enzyme-linked anti-immunoglobulin in antigen-coated tubes. Journal of Immunology 109:129–135
JohnstonA. W. B.,
BeringerJ. E.1975; Identification of theRhizobium strains in pea root nodules using genetic markers. Journal of General Microbiology 87:343–350
NakaneP. K.,
PierceG. B.1966; Enzyme-labelled antibodies: preparation and application for the localisation of antigens. Journal of Histochemistry and Cytochemistry 14:929–931
SchwinghamerE. A.,
DudmanW. F.1971; Evaluation of spectinomycin resistance as a marker for ecological studies withRhizobium spp. Journal of Applied Bacteriology 36:262–271
StuchburyT.,
ShiptonM.,
NorrisR.,
Malt-HouseJ. P. G.,
BrocklehurstK.,
HerbertJ. A. L.,
SuschitzkyH.1975; A reporter group delivery system with both absolute and selective specificity for thiolgroups and an improved fluorescent probe containing the 7-nitrobenzo-2-oxa-1,3- diazole moiety. Biochemical Journal 151:417–432
VollerA.,
BartlettD. E.,
ClarkM. F.,
AdamsA. N.1976; The detection of viruses by enzyme- linked immunosorbent assay (ELISA). Journal of General Virology 33:165–167
WestphalA.,
JannK.1965; Bacterial lipopoly- saccharides. Extraction with phenol-water and further applications of the procedure. Methods in Carbohydrate Chemistry 5:83–91