Abstract
Enterotoxigenic Escherichia coli (ETEC) strains are an important cause of bacterial diarrheal illness in humans and animals. Infections arising from ETEC could potentially be treated through the use of bacteriophage (phage) therapy, as phages encode for enzymes capable of bacterial cell lysis. vB_EcoP_SU7 was isolated from the Käppala wastewater treatment plant in Stockholm, Sweden, and propagated on an ETEC strain exhibiting the O:139 serovar. Transmission electron microscopy confirmed that vB_EcoP_SU7 belongs to the Podoviridae family and has the rare C3 morphotype of an elongated head. Bioinformatic analyses showed that the genome was 76,626 base pairs long and contained 35 genes with predicted functions. A total of 81 open reading frames encoding proteins with hypothetical function and two encoding proteins of no significant similarity were also found. A putative tRNA gene, which may aid in vB_EcoP_SU7’s translation, was also identified. Phylogenetic analyses showed that compared to other Podoviridae, vB_EcoP_SU7 is a rare Kuravirus and is closely related to E. coli phages with the uncommon C3 morphotype, such as ECBP2, EK010, vB_EcoP_EcoN5, and vB_EcoP_SU10. Phage vB_EcoP_SU7 has a narrow host range, infecting 11 out of the 137 E. coli strains tested, a latency period of 30 min, a burst size of 12 PFU/cell, and an adsorption rate of 8.78 × 10−9 mL/min five minutes post infection. With a limited host range and poor infection kinetics, it is unlikely that SU7 can be a standalone phage used for therapeutic purposes; rather, it must be used in combination with other phages for broad-spectrum therapeutic success.
Highlights
Escherichia coli is a common Gram-negative bacterium that is often found in the gastrointestinal tract of mammals and humans [1]
Transmission Electron Microscopy (TEM) confirms that SU7 is a phage belonging to the rare C3 morphotype of the Podoviridae family within the Caudovirales order
Occurring in less than 1% of Podoviridae virions, this rare morphotype has been observed among phages belonging to the Kuravirus genus and include the E. coli phages vB_EcoP_SU10, Paul, and phiEco32 [47,48,49,50]
Summary
Escherichia coli is a common Gram-negative bacterium that is often found in the gastrointestinal tract of mammals and humans [1]. While there are a vast number of strains of E. coli that live as a normal part of the commensal microflora 0.1% of the commensal microflora in humans) [2,3], there are a number of strains that are capable of causing disease [4]. Enterotoxigenic E. coli (ETEC) strains are among the major causative agents behind diarrheal diseases in low- and middle-income countries (often referred to as traveler’s diarrhea) and in animal farming [5,6]. ETEC infections are commonly treated with different antibiotics, such as fluoroquinolones (most used) and ciprofloxacin [6,8]. Due to the ongoing widespread misuse of antibacterial agents, bacteria such as ETEC have developed resistance against commonly used antibiotics [8,9]. Infections caused by a single species, such as E. coli, as well as those caused by multiple
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