Reaction of saprophytic bacteria from potato peel extracts and plant pathogenic bacteria in ELISA with antisera to Erwinia chrysanthemi (serogroup O1Ha)
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- Van der Wolf, J.M. & Gussenhoven, G.C. Netherlands Journal of Plant Pathology (1992) 98: 33. doi:10.1007/BF01998076
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The specificity of two antisera raised to whole cells ofErwinia chrysanthemi (Ech), serogroup O1Ha, was studied in double antibody sandwich (DAS-) ELISA with 100 strains of different plant pathogenic bacteria (PPB), including 39 Ech strains, and of one of these antisera with 900 saprophytic bacteria isolated from extracts of potato peelings of Dutch seed potatoes grown in several production areas.
All tested European Ech strains from potato reacted positively while no reactions were observed with any of the other plant pathogenic bacterial species. Two saprophytes (A254 and A256), both identified as pectinolyticPseudomonas fluorescens species, cross-reacted strongly with polyclonal antibodies against Ech. Non-specific reactions were found in DAS-ELISA with 16 saprophytes. The detection limits for the individual saprophytes varied between c. 105 and 109 cells.ml−1. The non-specific reactions were also found with monoclonal antibodies (mca 2A4) against a proteinase K resistent epitope of Ech and with antisera against other plant pathogens including an antiserum against potato virus YN. The non-specific reactions were observed in DAS-ELISA, but not in Ouchterlony double diffusion or immunofluorescence colonystaining, whereas A254 and A256 reacted in all tests, but only with antibodies against Ech. When in making dilution series potato peel extracts were used instead of phosphate buffered saline with 0.1% Tween 20, the 14 non-specifically reacting saprophytes only reacted at concentrations of 109 cells.ml−1 or higher. Only one of these 14 saprophytes was able to multiply on injured potato tuber tissue.
In contrast to most saprophytic strains, the saprophytes A254 and A256 reacted strongly in ELISA in dilutions series made with potato peel extracts. A256 was able to grow on potato tuber tissue but only under low oxygen conditions; A254 did not grow at all on potato tissue.
Defatted milk powder or bovine serum albumin added to the dilution buffer for the enzymeconjugated antibodies, drastically reduced the non-specific reactions, but not the reactions with A254 and A256.
To reduce the cross-reaction with A254, an Ech antiserum was absorbed with A254. This resulted in a substantial drop in antibody reaction with the homologous antigen in Ouchterlony double diffusion.