Lytic activity of the recombinant staphylococcal bacteriophage PhiH5 endolysin active against Staphylococcus aureus in milk.

The endolysin gene (lysH5) from the genome of the Staphylococcus aureus bacteriophage PhiH5 was cloned in Escherichia coli and characterized. The lysH5 gene encoded a protein (LysH5) whose calculated molecular mass and pI were 53.7 kDa and 8.7, respectively. Comparative analysis revealed that LysH5 significantly resembled other murein hydrolases encoded by staphylococcal phages. The modular organization of LysH5 comprised three putative domains, namely, CHAP (cysteine, histidine-dependent amidohydrolase/peptidase), amidase (L-muramoyl-L-alanine amidase), and SH3b (cell wall recognition). In turbidity reduction assays, the purified protein lysed bovine and human S. aureus, and human Staphylococcus epidermidis strains. Other bacteria belonging to different genera were not affected. The lytic activity was optimal at pH 7.0, 37 degrees C, and sensitive to high temperatures. The purified protein was able to kill rapidly S. aureus growing in pasteurized milk and the pathogen was not detected after 4 h of incubation at 37 degrees C. As far as we know, this is the first report to assess the antimicrobial activity of a phage endolysin which might be useful for novel biocontrol strategies in dairying.