Combined antimicrobial effect of phage-derived endolysin and depolymerase against biofilm-forming Salmonella Typhimurium

Combined antimicrobial activity of short peptide and phage-derived endolysin against antibiotic-resistant Salmonella Typhimurium

This study was designed to evaluate the combination effects of antimicrobial peptides (FK13 and FK16) and phage-encoded endolysin (LysPB32) on the inhibition of growth of polymyxin B-resistant Salmonella Typhimurium ATCC 19585 (STPMB). The inhibitory effects of FK13, FK16, and LysPB32 against STPMB were evaluated by using antimicrobial susceptibility, membrane permeability, biofilm reduction, cross-resistance, and mutant frequency assay. The minimum inhibitory concentrations (MICs) of FK13 and FK16 treated with LysPB32 (FK13+LysPB32 and FK16+LysPB32) against STPMB were decreased from more than 512 to 128 μg/ml and from 64 to 32 μg/ml, respectively. Compared to the control, the number of STPMB in the growing culture was reduced by 4.2 and 5.2 log CFU/ml, respectively, for FK13+LysPB32 and FK16+LysPB32 after 12-h incubation at 37 °C. All treatments (FK13, FK16, FK13+LysPB32, FK16+LysPB32) significantly increased the permeability of the outer membrane of STPMB. Biofilms were significantly decreased from OD600 of 0.6 to 0.16 for FK13+LysPB32 and from 0.6 to 0.13 for FK16+LysPB32. The ratios of MICs of erythromycin, ceftriaxone, polymyxin B, and ciprofloxacin to MIC of the control against STPMB were decreased to 0.50 for FK13+LysPB32 and FK16+LysPB32. The bactericidal activities of amikacin and gentamicin were enhanced for FK13+LysPB32 and FK16+LysPB32 (2-fold < MBC/MIC ratio). The mutant frequencies of STPMB to antibiotics were decreased when treated with FK13+LysPB32 and FK16+LysPB32. The results suggest that the combination of antimicrobial peptides and endolysins can be a promising strategy to control polymyxin B-resistant S. Typhimurium.

Characterization of a Salmonella abortus equi phage 4FS1 and its depolymerase

The significant economic losses caused by S. abortus equi in donkey husbandry have increased interest in exploring the potential of phages and their enzymes as control strategies. In this study, a S. abortus equi phage, designated 4FS1, was isolated from sewage at a donkey farm. Transmission electron microscopy (TEM) revealed a typical icosahedral head and a long, non-contractile tail. It exhibited a short latent period of 20 min and a burst size of 160 plaque-forming units (PFU) per cell. It demonstrated a broad host range, infecting 36 out of 60 salmonella strains, with an optimal multiplicity of infection (MOI) of 0.01 for S. abortus equi S1. The phage titer remained stable at 109 PFU/mL between 37°C and 50°C and exceeded 108 PFU/mL at pH from 5.0 to 10.0. After 1 h of UV exposure, the titer remained at 107 PFU/mL and showed no significant variation across NaCl concentrations from 2.5 to 15%. The genome of phage 4FS1 consists of a 42,485 bp linear double-stranded DNA molecule with a G + C content of 49.07%. Of the 56 predicted open reading frames (ORFs), 32 were functional annotated, with no virulence or drug resistance genes identified. ORF36 was predicted to encode a depolymerase responsible for endorhamnosidase activity. Recombinant expression of the Dpo36 protein in prokaryotes significantly reduced biofilm formation and removal. Combined with healthy donkey serum, Dpo36 inhibited bacterial growth in vitro and enhanced the survival rates of mice infected with S. abortus equi. These findings highlight the promising potential of phages and their depolymerases as novel therapeutic agents against S. abortus equi.

Antibacterial activity of bacteriophage-encoded endolysins against planktonic and biofilm cells of pathogenic Escherichia coli

This study was designed to assess the possibility of using bacteriophage-encoded endolysins for controlling planktonic and biofilm cells. The endolysins, LysEP114 and LysEP135, were obtained from plasmid vectors containing the endolysin genes derived from Escherichia coli phages. The high identity (>96 %) was observed between LysEP114 and LysEP135. LysEP114 and LysEP135 were characterized by pH, thermal, and lactic acid stability, lytic spectrum, antibacterial activity, and biofilm eradication. The molecular masses of LysEP114 and LysEP135 were 18.2 kDa, identified as muramidases. LysEP114 and LysEP135 showed high lytic activity against the outer membrane-permeabilized E. coli KCCM 40405 at below 37 °C, between pH 5 to 11, and below 70 mM of lactic acid. LysEP114 and LysEP135 showed the broad rang of lytic activity against E. coli KACC 10115, S. Typhimurium KCCM 40253, S. Typhimurium CCARM 8009, tetracycline-resistant S. Typhimurium, polymyxin B-resistant S. Typhimurium, chloramphenicol-resistant S. Typhimurium, K. pneumoniae ATCC 23357, K. pneumoniae CCARM 10237, and Shigella boydii KACC 10792. LysEP114 and LysEP135 effectively reduced the numbers of planktonic E. coli KCCM by 1.7 and 2.1 log, respectively, when treated with 50 mM lactic acid. The numbers of biofilm cells were reduced from 7.3 to 4.1 log CFU/ml and 2.2 log CFU/ml, respectively, when treated with LysEP114- and LysEP135 in the presence of 50 mM lactic acid. The results suggest that the endolysins in combination with lactic acid could be potential alternative therapeutic agents for controlling planktonic and biofilm cells.

Gram-negative endolysins: overcoming the outer membrane obstacle

Our ability to control the growth of Gram-negative bacterial pathogens is challenged by rising antimicrobial resistance and requires new approaches. Endolysins are phage-derived enzymes that degrade peptidoglycan and therefore offer potential as antimicrobial agents. However, the outer membrane (OM) of Gram-negative bacteria impedes the access of externally applied endolysins to peptidoglycan. This review highlights recent advances in the discovery and characterization of natural endolysins that can breach the OM, as well as chemical and engineering approaches that increase antimicrobial efficacy of endolysins against Gram-negative pathogens.