Abstract
Drug-resistant bacteria are a serious threat to global public health. Gram-positive bacterial endolysin preparations have been successfully used to fight Gram-positive bacteria as a novel antimicrobial replacement strategy. However, Gram-negative bacterial phage endolysins cannot be applied directly to destroy Gram-negative strains due to the externally inaccessible peptidoglycan layer of the cell wall; this has seriously hampered the development of endolysin-like antibiotics against Gram-negative bacteria. In this study, 3–12 hydrophobic amino acids were successively added to the C-terminus of Escherichia coli phage endolysin Lysep3 to create five different hydrophobic-modified endolysins. Compared with endogenous Lysep3, endolysins modified with hydrophobic amino acids surprisingly could kill E. coli from outside of the cell at the appropriate pH and endolysin concentration. The lysis ability of modified endolysins were enhanced with increasing numbers of hydrophobic amino acids at the C-terminus of endolysin. Thus, these findings demonstrate that the enhancement of hydrophobicity at the C-terminus enables the endolysin to act upon E. coli from the outside, representing a novel method of lysing Gram-negative antibiotic-resistant bacteria.
Highlights
The excessive use of antibiotics in clinical medicine and raising livestock have resulted in an increased prevalence of antibiotic-resistant strains (Morrill et al 2016)
Expression, and purification of fusion endolysins To explore the effect of hydrophobic amino acids on the ability of endolysins to get into the outer membrane of Gram-negative bacteria, different hydrophobic amino acids were added to the C-terminus of Lysep3, generating the constructs: Lysep3, Lysep3-3, Lysep3-5, Lysep3-7, Lysep3-12a, and Lysep3-12b (Fig. 1a)
Due to the special structure of the cell wall in Gram-negative bacteria, phage endolysins cannot lyse the bacteria from the outside of the cell, which is not the same with the Grampositive bacteria
Summary
The excessive use of antibiotics in clinical medicine and raising livestock have resulted in an increased prevalence of antibiotic-resistant strains (Morrill et al 2016). The ability of bacteria to resist antibiotics has been spread and strengthened through naturally occurring plasmids and bacteriophages. The problem of antibiotic resistance is worsening and represents a grave threat to human health (Tacconelli et al 2018). Lyse drug-resistant pathogens without affecting the commensal flora (Yang et al 2014). Bacteria are less likely to develop resistance to endolysins. Increased attention has recently been paid to studies of phage endolysins as
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