Open Access Highly Accessed Research article

Lysis-deficient phages as novel therapeutic agents for controlling bacterial infection

Vivek Daniel Paul12, Sudarson Sundarrajan1, Sanjeev Saravanan Rajagopalan1, Sukumar Hariharan1, Nanjundappa Kempashanaiah13, Sriram Padmanabhan14, Bharathi Sriram1* and Janakiraman Ramachandran1

Author Affiliations

1 Gangagen Biotechnologies Pvt Ltd, No. 12, 5th Cross, Raghavendra Layout, Tumkur Road, Yeshwantpur, Bangalore-560 022, India

2 Department of Molecular Genetics, University of Toronto, 1 King's College Circle, Toronto, ON M5S 1A8, Canada

3 Department of Animal Husbandry, Veterinary Dispensary, Yediyur, Kunigal Taluk, Tumkur- 572142, India

4 Lupin Limited, Biotechnology R & D, Gat #1156, Ghotawade Village, Mulshi Taluka, Pune-411042, India

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BMC Microbiology 2011, 11:195  doi:10.1186/1471-2180-11-195

Published: 31 August 2011

Abstract

Background

Interest in phage therapy has grown over the past decade due to the rapid emergence of antibiotic resistance in bacterial pathogens. However, the use of bacteriophages for therapeutic purposes has raised concerns over the potential for immune response, rapid toxin release by the lytic action of phages, and difficulty in dose determination in clinical situations. A phage that kills the target cell but is incapable of host cell lysis would alleviate these concerns without compromising efficacy.

Results

We developed a recombinant lysis-deficient Staphylococcus aureus phage P954, in which the endolysin gene was rendered nonfunctional by insertional inactivation. P954, a temperate phage, was lysogenized in S. aureus strain RN4220. The native endolysin gene on the prophage was replaced with an endolysin gene disrupted by the chloramphenicol acetyl transferase (cat) gene through homologous recombination using a plasmid construct. Lysogens carrying the recombinant phage were detected by growth in presence of chloramphenicol. Induction of the recombinant prophage did not result in host cell lysis, and the phage progeny were released by cell lysis with glass beads. The recombinant phage retained the endolysin-deficient genotype and formed plaques only when endolysin was supplemented. The host range of the recombinant phage was the same as that of the parent phage. To test the in vivo efficacy of the recombinant endolysin-deficient phage, immunocompromised mice were challenged with pathogenic S. aureus at a dose that results in 80% mortality (LD80). Treatment with the endolysin-deficient phage rescued mice from the fatal S. aureus infection.

Conclusions

A recombinant endolysin-deficient staphylococcal phage has been developed that is lethal to methicillin-resistant S. aureus without causing bacterial cell lysis. The phage was able to multiply in lytic mode utilizing a heterologous endolysin expressed from a plasmid in the propagation host. The recombinant phage effectively rescued mice from fatal S. aureus infection. To our knowledge this is the first report of a lysis-deficient staphylococcal phage.