Adhesiveness of the specific phages to yersiniae cells assessed by optical trapping

In recent years, there has been increasing interest in using bacteriophages in the complex therapy of some infectious diseases. Objectively, it is related to the spread of antibiotic resistance and a small number of side effects triggered by phages applied locally and parenterally. Yersiniae are no exception to this rule, but their interaction with virions has not been studied thoroughly. In three types of lytic Yersiniae bacteriophages are used for diagnostic purposes, which differ in specificity, virulence, and morphological features. We evaluated the interaction force between phages and bacteriae by optical trapping.

Materials and methods. Live Yersinia pseudotuberculosis and Y. pestis cells with different LPS structure and preparations of three bacteriophages — Pokrovskaya’s phage, d’Herelle’s phage (also named as the pseudotuberculosis phage) and the phage L-413C were used. The Pokrovskaya’s phage is well studied and widely used in diagnostics, but the mechanism of its adsorption on Y. pestis and Y. pseudotuberculosis cells is not well-understood. The phage L-413C lyses plague bacteria, while d’Herrel’s phage can lyse both pathogens. Virions were linked to the surface of aminated glass. Optically trapped microbial cells were approached to the glass surface and then retracted in the opposite direction. The amplitude of the leap was recalculated into force through calibration coefficients. The primary data were processed in the program “R”; statistical analysis was performed using “Matlab 7.0” and “Statistica 12”

Results and discussion. The analysis of histograms revealed the presence of a specific component in the «Y. pseudotuberculosis–d’Herrell’s phage» (Fmean = 7.46±3.52 pN) system, as well as in all pairs involving plague microbe. In the latter case, the interaction forces were comparable: 8.64±3.83 pN for d’Herelle’s phage,11.03±4.22 pN for Pokrovskaya’s phage, and 10.42±4.79 pN for phage L-413C. The average detachment force from the substrate treated with bovine serum albumin (BSA) was comparable for both cell types. Our results convincingly prove an opportunity for using the optical trapping to estimate interaction force in other «bacterium–phage» systems.