The inability of a bacteriophage to infect Staphylococcus aureus does not prevent it from specifically delivering a photosensitiser to the bacterium enabling its lethal photosensitisation

Abstract

Objectives: It has been demonstrated that the efficiency of lethal photosensitisation can be improved by covalently binding photosensitising agents to bacteriophage. In this study we have investigated whether a bacteriophage requires the capacity to infect the bacterium to enhance lethal photosensitisation when linked to a photosensitizer. Methods: Tin (IV) chlorin e6 (SnCe6) was conjugated to bacteriophage Φ11, a transducing phage which can infect Staphylococcus aureus NCTC 8235-4, but not EMRSA 16. The conjugate and appropriate controls, were incubated with these bacteria and either exposed to laser light at 632.8 nm or kept in the dark. Results: The SnCe6 / Φ11 conjugate achieved a statistically significant reduction in the number of viable bacteria of both 8325-4 and EMRSA 16 strains by 2.31 log10 and 2.63 log10 respectively. The conjugate could not however instigate lethal photosensitisation in E. coli. None of the other combinations of controls; such as an equivalent concentration of SnCe6 only, an equivalent titre of bacteriophage only or experiments conducted without laser light; yielded significant reductions in the number of viable bacteria recovered. Conclusions: The inability of a bacteriophage to infect S. aureus does not prevent it from specifically delivering a photosensitiser to a bacterium enabling its lethal photosensitisation.