The highly pathogenic bacterium Yersinia pestis is the causative agent of plague, a notorious infectious zoonotic disease. When transmitted from person to person as pneumonic plague via droplets, Y. pestis is highly contagious and in most cases is fatal if left untreated. Thus, when plague is suspected, rapid diagnosis is crucial, as a serious course of the infection is only averted by early antibiotic therapy. The bacterium is easy to cultivate, accessible and has a high potential for nefarious use such as bioterrorism. Highly specific, rapid and easy-to-use confirmatory diagnostic methods are required to reliably identify the pathogen independently from PCR-based methods or F1 antigen-based immunological detection. Yersinia pestis specific phages such as L-413C and ΦA1122 are already used for detection of Y. pestis in bacterial plaque or biosensor assays. Here, we made use of the host specificities conferred by phage receptor binding (or tail fiber/spike) proteins (RBP) for developing a specific, fast and simple fluorescence-microscopy-based detection method for Y. pestis. Genes of putative RBP of phages L-413C (gpH) and ΦA1122 (gp17) were fused with those of fluorescent proteins and recombinant receptor-reporter fusion proteins were produced heterologously in Escherichia coli. When first tested on attenuated Y. pestis strain EV76, RBP-reporters bound to the bacterial cell surface. This assay could be completed within a few minutes using live or formaldehyde-inactivated cells. Specificity tests using cultures of closely related Yersinia species and several inactivated fully virulent Y. pestis strains exhibited high specificities of the RBP-reporters against Y. pestis. The L-413C RBP proved to be especially specific, as it only detected Y. pestis at all temperatures tested, whereas the RBP of ΦA1122 also bound to Y. pseudotuberculosis strains at 37 °C (but not at 28, 20 or 6 °C). Finally, the Y. pestis-specific capsule, produced when grown at 37 °C, significantly reduced binding of phage ΦA1122 RBP, whereas the capsule only slightly diminished binding of L-413C RBP.
Specific Detection of Yersinia pestis Based on Receptor Binding Proteins of Phages
