Indirect immunofluorescence colony staining method for detecting bacterial pathogens of tomato

An indirect immunofluorescence colony staining method was developed for the detection of important seed-borne bacterial pathogens of tomato. The method involves the use of specific antiserum for initial binding of target bacteria and visualization of positive colonies with a commercially available secondary antiserum conjugated with FITC and observed under a fluorescence microscope. The indirect method is especially suitable for laboratories, seed companies, and quarantine stations which have no facilities for conjugation of primary antiserum. It is more economical and overcomes the problems generally encountered with variable conjugate quality in new batches of conjugates prepared from the same stock of primary antiserum. The assay is easy to perform and results can be easily assessed by visual scoring or image analyser. Results are available in 4-5 days as compared to 30-45 days in traditional methods. The resulting bacterial culture can be tested by PCR or host infectivity and a culture can be stored for future reference. Used in combination with highly specific antibodies (commercially available monoclonal and recombinant antibodies) it can be used as a very sensitive detection tool and has application potential in localization studies as well. Choosing the right secondary conjugate is however necessary to get best results in the assay.