A novel phage lysin Lys19 can serve as potential biocontrol agent against Clostridium perfringens and Streptococcus suis.

Food contamination with Clostridium perfringens (C. perfringens) and Streptococcus suis (S. suis) may lead to severe foodborne illnesses in humans, and new effective strategies are needed to limit foodborne microbial contamination. In this study, a novel C. perfringens phage, XBG01, was isolated, and its lysin, Lys19, was characterized. Lys19 consists of an N-terminal N-acetylmuramoyl-L-alanine amidase catalytic domain and a C-terminal binding domain comprising two 35-residue repeats. H13, E26, H81, R124, and E146 were identified as key sites for maintaining the activity of the catalytic domain. The activity of the catalytic domain is independent of the presence of metal ions and is not affected by the binding domain. Notably, in addition to type A C. perfringens, Lys19 can also efficiently lyse 2, 3, 7, 9 and 12 serotypes of S. suis. This is the first reported C. perfringens phage lysin with a cross-bacterial species lytic function. It maintains stable activity in the temperature range of 4-55 °C and pH range of 3-9, and can effectively prevent and eliminate strong biofilms formed by C. perfringens. The bacterial viability on lettuce was significantly lower in the group treated with lysin Lys19 than in the PBS group, and 88.75 % of C. perfringens were killed within 15 min. In addition, Lys19 treatment significantly reduced the bacterial load in raw pork by about 84.65 % at a temperature of 4 °C within 12 h. These results indicate that Lys19 has potential applications in controlling C. perfringens and S. suis in lettuce and meat.