Foodborne Shiga toxin-producing Escherichia coli (STEC) cause severe diarrhea and hemolytic uremic syndrome (HUS) in humans. However, traditional methods for STEC sterilization are difficult to apply to fresh food. To control the pathogen, phage infecting E. coli O157:H7 were isolated and characterized. The isolated phage vB_EcoM-ECP26 had an icosahedral head and a contractile tail, and was classified as belonging to the Myoviridae family. The phage showed a broad host range against STEC and exhibited a large burst size of 1914 PFU/cell. The phage was highly stable at high temperatures (65 °C) and wide ranges of pH (4-10). The genome of vB_EcoM-ECP26 consists of 136,993 nucleotides, 214 open reading frames, and does not contain lysogenicity-related genes. Phylogenetic analysis showed that vB_ EcoM-ECP26 is a V5-like species. STEC O157 growth was inhibited by vB_EcoM-ECP26 for 8 h. Furthermore, this phage not only significantly decreased the STEC population (p < 0.05), but also persisted in fresh lettuce at 4 °C for 5 days. Therefore, these results reveal that the novel lytic phage vB_EcoM-ECP26 could be a useful agent for the control of foodborne STEC.

Escherichia coli O157:H7 is a global concern that causes serious diseases, such as hemolytic uremic syndrome and bloody diarrhea. To control E. coli O157:H7 in food, a novel siphophage, BECP10, that targets the O157 serotype was isolated and characterized. Unlike other E. coli phages, BECP10 can only infect E. coli O157 strains, and thus, did not infect other strains. The 48 kbp genome of BECP10 contained 76 open reading frames (ORFs), including 33 putative functional ORFs. The phage did not contain lysogeny-related modules or toxin-associated genes, suggesting that the phage might be strictly lytic. The tail spike protein (TSP) sequence had very low homology with the reported T1-like phages, indicating that TSP might be related to this unique host spectrum. The specific O-antigen residue of E. coli O157:H7 may be a key factor for phage infection by adsorption and receptor identification. The phage exhibited strong antibacterial activity against E. coli O157:H7 over a broad pH range and showed little development of phage-insensitive mutants. The phage sustained viability on the burger patties and reduced E. coli O157:H7 to a non-detectable level without the emergence of resistant cells at low temperatures for five days. Therefore, phage BECP10 might be a good biocontrol agent for E. coli O157:H7-contaminated food matrices.

With an increase in the consumption of non-heated fresh food, foodborne shiga toxin-producing Escherichia coli (STEC) has emerged as one of the most problematic pathogens worldwide. Endolysin, a bacteriophage-derived lysis protein, is able to lyse the target bacteria without any special resistance, and thus has been garnering interest as a powerful antimicrobial agent. In this study, rV5-like phage endolysin targeting E. coli O157:H7, named as LysECP26, was identified and purified. This endolysin had a lysozyme-like catalytic domain, but differed markedly from the sequence of lambda phage endolysin. LysECP26 exhibited strong activity with a broad lytic spectrum against various gram-negative strains (29/29) and was relatively stable at a broad temperature range (4°C-55°C). The optimum temperature and pH ranges of LysECP26 were identified at 37°C-42°C and pH 7-8, respectively. NaCl supplementation did not affect the lytic activity. Although LysECP26 was limited in that it could not pass the outer membrane, E. coli O157: H7 could be effectively controlled by adding ethylenediaminetetraacetic acid (EDTA) and citric acid (1.44 and 1.14 log CFU/ml) within 30 min. Therefore, LysECP26 may serve as an effective biocontrol agent for gram-negative pathogens, including E. coli O157:H7.

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The increasing prevalence of foodborne diseases caused by Escherichia coli O157:H7 as well as its ability to form biofilms poses major threats to public health worldwide. With increasing concerns about the limitations of current disinfectant treatments, phage-derived depolymerases may be used as promising biocontrol agents. Therefore, in this study, the characterization, purification, and application of a novel phage depolymerase, Dpo10, specifically targeting the lipopolysaccharides of E. coli O157, was performed. Dpo10, with a molecular mass of 98 kDa, was predicted to possess pectate lyase activity via genome analysis and considered to act as a receptor-binding protein of the phage. We confirmed that the purified Dpo10 showed O-polysaccharide degrading activity only for the E. coli O157 strains by observing its opaque halo. Dpo10 maintained stable enzymatic activities across a wide range of temperature conditions under 55°C and mild basic pH. Notably, Dpo10 did not inhibit bacterial growth but significantly increased the complement-mediated serum lysis of E. coli O157 by degrading its O-polysaccharides. Moreover, Dpo10 inhibited the biofilm formation against E. coli O157 on abiotic polystyrene by 8-fold and stainless steel by 2.56 log CFU/coupon. This inhibition was visually confirmed via fieldemission scanning electron microscopy. Therefore, the novel depolymerase from E. coli siphophage exhibits specific binding and lytic activities on the lipopolysaccharide of E. coli O157 and may be used as a promising anti-biofilm agent against the E. coli O157:H7 strain.

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