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The overuse of antibiotics has resulted in the emergence of antibiotic-resistant bacteria, which presents an urgent need for new antimicrobial agents. At present, antimicrobial peptides have attracted a great deal of attention from researchers. However, antimicrobial peptides often affect a broad range of microorganisms, including the normal flora in a host organism. In the present study, we designed a novel hybrid antimicrobial peptide, expressed the hybrid peptide, and studied its specific target. The hybrid peptide, named T-catesbeianin-1, which includes the FyuA-binding domain of pesticin and the peptide catesbeianin-1, was designed and expressed in Pichia pastoris X-33. Then, we determined the antimicrobial activity, cytotoxicity, and specific target of the peptide. T-catesbeianin-1 has strong antimicrobial activity and binds to FyuA to inhibit or kill Escherichia coli present in clinical specimens and mixed-species culture. In summary, these findings suggested that T-catesbeianin-1 might be promising and specific antibiotic agent for therapeutic application against fyuA + E. coli., (Copyright © 2018 European Peptide Society and John Wiley & Sons, Ltd.)

In recent years, after the emergence of a large number of multidrug-resistant bacteria, phages and phage-associated products for the prevention and control of bacterial disease have revealed prominent advantages as compared with antibiotics. However, bacteria are susceptible to becoming phage-resistant, thus severely limiting the application of phage therapy. In this study, Escherichia coli cells were incubated with lytic bacteriophages to obtain mutants that were resistant to the lytic phages. Then, bacteriophages against the phage-resistant variants were isolated and subsequently mixed with the original lytic phage to prepare a novel phage cocktail for bactericidal use. The data showed that our phage cocktail not only had notable bactericidal effects, including a widened host range and rapid lysis, but also decreased the generation and mutation frequency of phage-resistant strains in vitro. In addition, we tested our cocktail in a murine bacteremia model. The results suggested that compared with the single phage, fewer phage-resistant bacteria appeared during the treatment of phage cocktail, thus prolonging the usable time of the phage cocktail and improving its therapeutic effect in phage applications. Importantly, our preparation method of phage cocktail was proved to be generalizable. Because the bacteriophage against the phage-resistant strain is an ideal guard that promptly attacks potential phage resistance, this guard-killer dual-function phage cocktail provides a novel strategy for phage therapy that allows the natural ecology to be sustained.

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.

Bacteriophages represent one prospect for preventing and treating multi-drug-resistant Escherichia coli. In this study, we have isolated a novel E. coli-specific bacteriophage and characterised its biological properties. vB_EcoM-ep3 has a broad host range and was able to lyse 9 out of 15 clinical isolates of multi-drug-resistant pathogenic E. coli from chickens. The optimal multiplicity of infection for vB_EcoM-ep3 in host bacteria was 0.01. vB_EcoM-ep3 was thermostable at temperatures below 50 °C for up to 60 min. Electron microscopy demonstrated that vB_EcoM-ep3 belongs to Myoviridae. The vB_EcoM-ep3 genome contained 42,351 pairs of nucleotides with a GC content of 53.35 %. There were 52 predicted open reading frames that appeared to overlap and have a modular structure. Phylogenetic analysis indicates that the closest evolutionary relative to vB_EcoM-ep3 is the previously reported E. coli phage vB_EcoM_ECO1230-10. However, there was no homology between reported E. coli phage lysins and the vB_EcoM-ep3 lysin gene. Lysep3 was 58 % similar to the Pseudomonas phage PPpW-3 lysin despite showing no similarities at the gene sequence level. And Lysep3 has good lysis activity.

Infections caused by antibiotic-resistant Escherichia coli are a threat to human and animal health globally. Phage therapy has made great progress for the treatment of drug-resistant infections, but it is still unclear whether E. coli resistance to antibiotics could change the lysis ability of phages. In this study, we demonstrate that over expression of AmpC, an important β-lactamase for ampicillin resistance, promotes lysis of E. coli by phage utilizing OmpA as a receptor. E. coli strains expressing more AmpC showed higher levels of OmpA, an E. coli outer membrane protein known to serve as a receptor for T-even phages, which resulted in increased adsorption and lysis by the phage tested in this study. These data demonstrate that increased ampicillin resistance can increase the sensitivity of E. coli to some lytic phage, which provides evidence for the feasibility of synergistic application of phage and antibiotics. [ABSTRACT FROM AUTHOR]

LysGH15, a phage endolysin, exhibits a particularly broad lytic spectrum against Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA). Sequence analysis reveals that this endolysin contains a C-terminal cell wall binding domain (SH3b), which causes the endolysin to bind to host strains. In this study, the substrate binding affinity of the SH3b domain (LysGH15B) was evaluated. A fusion protein of LysGH15B and green fluorescent protein (LysGH15B-GFP) were cloned and expressed in Escherichia coli. Laser scanning confocal microscopy was used to detect the fluorescence of the treated cells irradiated at different excitation wavelengths and to determine the binding activity of LysGH15B-GFP and GFP. We found that LysGH15B-GFP not only generated green fluorescence, but, more importantly, also displayed specific affinity to staphylococcal isolates, especially MRSA. In contrast, the single GFP did not display any binding activity. The high affinity was attributed to the portion of LysGH15B and the binding activity of the fusion protein was specific to staphylococci. This study provides an insight into the SH3b domain of LysGH15. The specific binding activity may cause LysGH15B to serve as an anchoring device, and offer an alternative approach for cell surface attachment onto staphylococci. [ABSTRACT FROM AUTHOR]