Isolation and Characterization of Two Lytic Phages Ahp1 and Ahp2 of Aeromonas hydrophila
| Autor: | WANG, JIAN-BIN, 王建斌 |
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| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 Aeromonas hydrohpila is known as an opportunistic pathogenic bacterium, which can cause furunculosis and fin rot in fishes and septicaemia and gastrointestinal infection in humans. Nowadays, multidrug-resistant bacteria (MDRB) are increasingly being reported worldwide. Instead of antibiotics, bacteriophage therapy is considered as a possible prophylactic and therapeutic alternative treatment for bacterial infections. Twenty-four phages with different morphologies and host range were isolated from environmental sewages. Two of them, designated Ahp1 and Ahp2, were further studied. Electron microscopy revealed Ahp1 to a podophage with an isometric head (62 nm in diameter), and a short tail (12.5 nm in length), and Ahp2 to a myophage with an isometric head (69.6 nm in diameter), a long tail (132.9 nm in length), a base plate (25.3 nm in width), and tail fibers. Both of them are linear double-stranded DNA phages with genome size of 42 kb and 47 kb, respectively, as estimated by pulsed-field gel electrophoresis. After 2 minutes of infection, Ahp1 can reach 96% of the adsorption rate, while Ahp2 achieves the same rate of adsorption after 18 minutes of infection. One-step growth analysis showed that the latent period of both were 15 min, and burst size of Ahp1 and Ahp2 were 112 and 102 pfu per infecting cell, respectively. On the basis of high degrees of similarity in overall genome organization and among most of the corresponding ORFs, as well as phylogenetic relatedness among their DNA polymerase, RNA polymerase and major capsid proteins, we propose a new subgroup, designated Ahp1-like subgroup. This subgroup contains Ahp1 and members previously belonging to phiKMV-like subgroup, phiAS7, phi80-18, GAP227, phiR8-01, and ISAO8. Based on similarity to genes from other related phages, the structural genes of Ahp2 were modularly clustered in terminase-portal-head-baseplate-tail fibers, similar to phages including VP58.5, VP882, MAR, VHML, and phiHAP-1, which are members of N15-like temperate phages. Comparative analyses also show that Ahp2 presents phylogenetic relationship with those of N15-like phages. We thus propose Ahp2 a new member of N15-like phage family, although lacking of complete set of genome maintenance and lysogeny control modules except for a parA-like protein and an integrase detected in the Ahp2 genome. The host range test showed that among 42 A. hydrophila strains including standard strains, clinical and environmental isolates, only 6 were susceptible to Ahp1 (infection rate was 14.3%), and 25 susceptible to Ahp2 (infection rate was 59.5%). None of the 7 none A. hydrophila strains were infected by Ahp1 and Ahp2. It suggests that Ahp1 is a phage with narrow host range, however, Ahp2 has a wide host range and seems have the potential to be applied in the phage therapy to this bacterial infection. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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