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Open Access Research article

Antistaphylococcal activity of bacteriophage derived chimeric protein P128

Aradhana A Vipra1, Srividya Narayanamurthy Desai1, Panchali Roy1, Raghu Patil1, Juliet Mohan Raj1, Nagalakshmi Narasimhaswamy13, Vivek Daniel Paul12, Ravisha Chikkamadaiah1 and Bharathi Sriram1*

Author Affiliations

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

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

3 Lecturer, Department of Microbiology, Melaka Manipal Medical College, Manipal Campus, Manipal 576 104, Karnataka, India

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BMC Microbiology 2012, 12:41  doi:10.1186/1471-2180-12-41

Published: 22 March 2012

Abstract

Background

Bacterial drug resistance is one of the most significant challenges to human health today. In particular, effective antibacterial agents against methicillin-resistant Staphylococcus aureus (MRSA) are urgently needed. A causal relationship between nasal commensal S. aureus and infection has been reported. Accordingly, elimination of nasal S. aureus reduces the risk of infection. Enzymes that degrade bacterial cell walls show promise as antibacterial agents. Bacteriophage-encoded bacterial cell wall-degrading enzymes exhibit intrinsic bactericidal activity. P128 is a chimeric protein that combines the lethal activity of the phage tail-associated muralytic enzyme of Phage K and the staphylococcal cell wall targeting-domain (SH3b) of lysostaphin.

Here we report results of in vitro studies evaluating the susceptibility of staphylococcal strains to this novel protein.

Results

Using the broth microdilution method adapted for lysostaphin, we found that P128 is effective against S. aureus clinical strains including MRSA, methicillin-sensitive S. aureus (MSSA), and a mupirocin-resistant S. aureus. Minimum bactericidal concentrations and minimum inhibitory concentrations of P128 (1-64 μg/mL) were similar across the 32 S. aureus strains tested, demonstrating its bactericidal nature.

In time-kill assays, P128 reduced colony-forming units by 99.99% within 1 h and inhibited growth up to 24 h.

In an assay simulating topical application of P128 to skin or other biological surfaces, P128 hydrogel was efficacious when layered on cells seeded on solid media. P128 hydrogel was lethal to Staphylococci recovered from nares of healthy people and treated without any processing or culturing steps, indicating its in situ efficacy. This methodology used for in vitro assessment of P128 as an agent for eradicating nasal carriage is unique.

Conclusions

The novel chimeric protein P128 is a staphylococcal cell wall-degrading enzyme under development for clearance of S. aureus nasal colonization and MRSA infection. The protein is active against globally prevalent antibiotic-resistant clinical isolates and other clinically significant staphylococcal species including S. epidermidis. The P128 hydrogel formulation was bactericidal against Staphylococci including S. aureus recovered from the nares of 31 healthy people, demonstrating its in situ efficacy.