1. Phages ST7, ST70, ST79 and ST88 have isometric heads (54 nm in diameter) and long contractile tails (148 nm in length and 17 nm in width) with long tail sheets and tail fibers while phages ST2 and ST96 have an average head diameter of 60 nm

with shorter tail sheets without tail fibers (tail length of 27 and 60 nm). From the morphology and nucleic acid types of genetic material, typing was based on guidelines of the International Committee on Taxonomy of Viruses (ICTV) (Ackermann, 2003), all phages belong to Myoviridae family and Bradley’s group A1 (Ackermann, 2001). In this study, all phage nucleic acids were dsDNA. CX-5461 molecular weight PstI and XhoI restriction enzymes provided distinguishable patterns after separation by agarose gel electrophoresis (Fig. 2). The estimated genome size of ST2, ST7, ST70, ST79, ST88 and ST96 phages were 40.9, 32.5, 24.0, 31.7, 32.3 and 54.6 kb. The ST7 and ST88 yielded very similar digestion patterns with two

enzymes, had similar genome sizes and their morphology under an electron microscope looked similar. Nevertheless, further investigations PD0325901 purchase should be made before it can be concluded as to whether they are the same phage. The ST2, ST7, ST70, ST79, ST88 and ST96 phages were able to lyse 78%, 41%, 65%, 71%, 41% and 67% of tested B. pseudomallei isolates. Only ST2 and ST96 phages could lyse B. thailandensis and all phages formed tiny clear plaques on B. mallei lawn. None of the phages could form any plaques on a wide range of other Gram-negative or Gram-positive bacteria tested in this

experiment (Table 1). The highest phage titer PIK-5 was obtained by infection of B. pseudomallei P37 (1 × 109 CFU mL−1) with ST79 and ST96 at an optimal MOI of 0.1. They were able to dramatically reduce OD550 nm of B. pseudomallei P37 in liquid culture from 0.3 OD550 nm to a complete lysis (OD almost zero) within 5 h after phage addition. The number of bacteria tended to increase again after 12 h (Fig. 3). The experiment was performed in triplicate. Phage ST79 was selected for further growth parameter characterization as this novel lytic phage had a broader host range of tested B. pseudomallei isolates. The eclipse and latent periods were 20 and 30 min. The average burst size, calculated by the ratio of the final count of liberated phage particles to the initial count of infected bacterial cells during the latent period, was 304 PFU per infected cell at 37 °C (Fig. 4). The experiment was performed in triplicate. Since 1959, over 5100 phages have been examined by electron microscopy, of which 96% are tailed phages belonging to Siphoviridae (61%), Myoviridae (25%) and Podoviridae (14%) (Ackermann, 2003). Phages are abundant in the environment and play an important role in the ecosystem. Several lytic phages have been isolated and characterized for therapeutic usage in animals and humans such as GJ1-GJ6, which are active against O149 enterotoxigenic E. coli, e11/2, e4/1c and pp01 against E. coli O157:H7, FGCSSa1 against Salmonella spp.