Endolysin LysSA97 is synergistic with carvacrol in controlling Staphylococcus aureus in foods

LysSA97 is an endolysin encoded by the bacteriophage SA97, the genome sequence of which has been recently revealed. LysSA97 has lytic activity against a variety of Staphylococcus strains that cause foodborne illness. In order to improve its potential as a biocontrol agent against Staphylococcus, various types of essential oil-derived active compounds were tested in combination with LysSA97; carvacrol exhibited significant synergistic effects when combined with LysSA97. The synergistic antimicrobial activity between endolysin and carvacrol in food products, including milk and beef, were investigated. While LysSA97 (376 nM) and carvacrol (3.33 mM) showed 0.8 ± 0.2 and 1.0 ± 0.0 log CFU/mL reduction in Staphylococcus aureus cells, respectively; when applied alone in bacterial culture, the cocktail containing both at the same concentrations exhibited a bacterial decrease of 4.5 ± 0.2 log CFU/mL. The synergistic activity of carvacrol was also reproduced in combination with other endolysins, and their cooperative bactericidal effects were validated in ten additional S. aureus strains, including two methicillin-resistant S. aureus (MRSA), suggesting the wide application of carvacrol as a bactericidal agent coupled with endolysin. When LysSA97 and carvacrol were used in combination in foods, the synergistic activity appeared to be influenced by the total lipid content of foods, and bacteria in skim milk were more drastically inactivated than those in whole milk. Therefore, this is the first report demonstrating that endolysin and carvacrol act synergistically to inactivate S. aureus in food products.