Bactericidal synergism between engineered endolysin Lysin1902 and tea polyphenols against Escherichia coli O157:H7 in various food products

The endolysin Lysin1902 has bacteriolytic activity but faces challenges in penetrating the bacterial outer membrane (OM). In this study, Lysin1902 was systematically modified to produce the recombinant protein Lysin1902-HP-PC. Although the modification did not affect its inability to cross the bacterial OM, it enhanced its resistance to temperature, pH, and ionic stress. Lysin1902-HP-PC showed a broader antibacterial spectrum compared to Lysin1902. Moreover, when combined with natural tea polyphenols (TP) at 0.3 mg/mL of Lysin1902-HP-PC, the bactericidal concentration of TP was effectively reduced from 1.2 to 0.3 mg/mL while maintaining its antimicrobial effect for over 10 h. A 1:1 ratio combination of Lysin1902-HP-PC and TP at 0.3 mg/mL effectively controlled the bacterial load of Escherichia coli O157:H7 in milk, beef, and lettuce at both 24 and 37 °C. Additionally, this combination treatment efficiently eliminated biofilms on both polystyrene and stainless steel surfaces. The results of our study demonstrated that the combined bactericidal mechanism is initiated by TP-induced damage to the bacterial OM, facilitating the entry of Lysin1902-HP-PC. Subsequently, Lysin1902-HP-PC targeted the bacterial cell wall and destroyed its integrity, thereby disrupting the physiological metabolism of the bacterial cells and causing bacterial cell lysis.