| Summary: | Antimicrobial resistance (AMR) is considered as one of the greatest threats to human public health and in agriculture and food security. To address this threat, a Global Action Plan encourages development of alternatives to antibiotics, including the use of bacteriophage to control infections. A large proportion of transmissible antibiotic resistance is encoded on conjugative plasmids. Transmission requires sex pili and a sex pilus targeting (SPS) phage could provide a selection against plasmid carriage.
The aim of this research is to isolate novel SPS phage to tackle AMR bacteria. Fifteen SPS phages were isolated, eleven were ssDNA phages in the Inoviridae family and four were ssRNA phages of the Leviviridae family. All phages were able to infect strains with the F plasmid but there was some phage plasmid specificity observed on different F like plasmid field isolates. Phylogenetic analysis of the 11 ssDNA phages genomes and protein pIII confirmed that they belong to genus Inovirus and are highly similar to filamentous (Ff) phages (M13, fd, f1). Three of the ssRNA phages were highly similar to genus Levivirus and the remaining ssRNA phage was similar to Allolevivirus. Two ssDNA phages R4 and R7, and ssRNA phage R13 represent a new species of Inovirus and Allolevivirus, respectively under ICVCN guidelines. All the phages demonstrated good stability under various conditions of temperature, pH and detergent.
One step growth analysis and plasmid loss kinetics of selected ssDNA and ssRNA phages were tested against strains containing derepressed and repressed plasmids. Phage growth on derepressed plasmid hosts had a short latent period and large burst size compared to a longer latent period with shorter rise period and burst size observed on repressed plasmid hosts. Selected phages demonstrated ca. 60% plasmid loss on derepressed hosts. Selection was limited on more repressed plasmid hosts, with a minimum loss of 0% and a maximum loss of 14%. These results suggest that treatment with phage will have variable efficacy in reducing plasmid borne AMR and that repression may pose a limit on the effectiveness of this approach to treat or reduce infections by targeting the plasmids. However, further investigations are required to fully understand SPS phage impact under additional environmental selective conditions.
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