Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/21/2014
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Staphylococcus S. aureus is a Gram-positive pathogen relevant for both human and animal health. It is one of the most common causes of nosocomial infections and associated with a wide range of life-threatening human diseases. As the major causative agent of bovine mastitis, it also has significant impact on agriculture worldwide. With multi-drug resistant S. aureus strains (e.g. methicillin-resistant S. aureus; MRSA) becoming increasingly prevalent, alternative therapeutics are urgently needed. Bacteriophage endolysins are capable of killing Gram-positive bacteria when exposed externally and therefore present a promising source of putative antimicrobials against these pathogens. In this work, we comparatively characterized nine staphylococcal peptidoglycan hydrolases featuring SH3b cell wall binding domains and representing five homology groups and four stand-alone proteins. They displayed varying degrees of lytic activity in vitro in zymograms, turbidity reduction and plate lysis assays, against a comprehensive set of strains including cell surface mutants and drug-resistant strains, and proved effective against static S. aureus biofilms. Binding studies with GFP-tagged SH3b domains indicated that these binding modules require an intact penta-glycine bridge for full binding activity and that wall teichoic acids interfere with SH3b domain cell wall binding. In a mouse model of systemic MRSA infection, six of nine lysins provided 100% protection from death by bacteremia, whereas only approximately 20% of animals treated with buffer or oxacillin survived until 48 hours post infection. In mice treated with any of the six effective enzymes, health conditions markedly improved during the course of the treatment, similar to mice treated with vancomycin, and animals were free of symptoms at the end of the experiment. Interestingly, despite a similar modular architecture among 8 enzymes (two N-terminal lytic domains and a C-terminal cell wall binding domain), one enzyme (phage 2638a endolysin) harbors an evolutionarily divergent catalytic domain that unexpectedly shares a conserved peptidoglycan cut site with the other 8 enzymes (mass spectrometry of peptidoglycan digestion products), suggesting a stringent control of these endolysin cut sites as evidenced by convergent evolution.