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“Background Despite their relatively small size and apparent simplicity, double-stranded DNA bacteriophages propagate by a tightly programmed infection process which involves a number of steps. Adsorption of the phage to the bacterial cell wall precedes injection of the nucleic acid and subsequent DNA replication, eventually giving raise to new phage particles

that are released after lysis of the host. Muralytic enzymes play essential roles in the life cycle of phages by degrading the peptidoglycan (PG) of the bacterial cell wall, facilitating the entry and eventual release of mature phage particles. Many DNA-tailed phages employ the holin-endolysin lysis system to release their progeny. Holins usually form large pores in the cytoplasmic membrane of the host allowing the endolysin to gain access to and hydrolyze GPCR & G Protein inhibitor the PG layer [1]. In addition to endolysins which are synthesized at the late stage of the

lytic cycle, virions often harbour murein hydrolases that locally degrade the PG in order to facilitate the entry of phage DNA during infection. Selleck Kinase Inhibitor Library These virion proteins are responsible of the “”lysis from without”" phenomenon caused by some phages when adsorbed onto the host cell in very high numbers [2]. Virion-associated murein hydrolases appear to be widespread in bacteriophages infecting both Gram-negative and Gram-positive bacteria as shown by zymograms of fully assembled virions and homology analysis of sequenced phage/prophage genomes [3]. Several phages infecting Gram negative hosts contain hydrolytic activities at a variety of locations within the virions. A protein with N-acetylmuramidase activity is often anchored to the base plate structure, as in the T4 virion tail [4]. Similarly, a lytic endopeptidase was found to be associated with the nucleocapsid of the double-stranded RNA bacteriophage Φ6 infecting either Pseudomonas syringae [5]. In the T7 bacteriophage, gp16 is an internal

head protein with transglycosylase activity that is ejected into the cell at the initiation of infection but is required only when the cell wall is highly cross-linked [6]. The presence of muralytic activities in virions infecting Gram-positive bacteria has also been demonstrated. PG hydrolase activities have been described in the virions for S. aureus phages Φ11 and Φ85 [3], phiMR11 [7], P68 [8] and in the Lactococcus lactis phage Tuc2009 [9]. S. aureus is an important human pathogen that has demonstrated a unique ability to acquire antibiotic resistance traits at high frequency and can cause numerous serious diseases [http://​www.​medicinenet.​com/​staph_​infection/​article.​htm] including food poisoning [10, 11]. In the last few years, there has been a dramatic increase in the incidence of community-associated methicillin- and multi-drug-resistant S. aureus infections that can limit therapeutic options [12]. Therefore, there is a growing demand of new anti-staphylococcal agents.