The N-terminal and central domain of colicin A enables phage lysin to lyse Escherichia coli extracellularly.

Multidrug-resistant Escherichia coli has seriously threatened antibiotic resources and international public health. Bacteriophage lysin preparations have been widely considered as valid agents for solving multidrug resistances. Many lysins have been derived to treat diseases caused by Gram-positive bacteria, but only a few lysin preparations have been found that successively treat diseases caused by Gram-negative bacteria. The outer membrane of Gram-negative bacteria effectively blocks the interactions between peptidoglycan in the periplasmic space and bacteriophage lysins, which therefore hampers the antimicrobial effects of bacteriophage lysins. In this study, a new fusion protein (Colicin-Lysep3) was constructed by fusing the translocation and receptor binding domains of colicin A with an E. coli phage lysin, which endows Colicin-Lysep3 bactericidal activity against E. coli from outside of Gram-negative bacteria. These results show that Colicin-Lysep3 could lyse the E. coli broadly in vitro and significantly reduce the number of E. coli in an intestinal infection mouse model. Overall, our findings first demonstrated that a colicin A fragment could enable a bacteriophage lysin to lyse E. coli from the outside, promoting the application of phage lysin preparations in control of Gram-negative bacteria.