Detection of Individual Microbial Pathogens by Proximity Ligation

Background: Nucleic acid amplification allows the detection of single infectious agents. Protein-based assays, although they provide information on ongoing infections, have substantially less detection sensitivity. Methods: We used proximity ligation reactions to detect proteins on bacteria and virus particles via nucleic acid amplification. Antibodies recognizing viral or bacterial surface proteins were equipped with DNA strands that could be joined by ligation when several antibodies were bound in proximity to surface proteins of individual infectious agents. Results: Detection sensitivities similar to those of nucleic acid-based detection reactions were achieved directly in infected samples for a parvovirus and an intracellular bacterium. Conclusions: This method enables detection of ligated DNA strands with good sensitivity by real-time PCR and could be of value for early diagnosis of infectious disease and in biodefense.