Prevalence and Diversity of Coliphages in Dhaka, Bangladesh and Their Lytic Potentials against Pathogenic Bacteria

Aim: Dhaka is a flood-prone city with a high prevalence of diarrhoeal diseases. This study investigated the natural reservoirs and diversity of coliphages in Dhaka to establish phage strains of potential use in antidiarrhoeal therapy.

Materials and Methods: 296 surface water samples and 20 faecal samples of hospitalised diarrhoea patients were collected during April-September 2012 and phages isolated were used in infecting 67 strains of Escherichia coli, 20 strains of Shigella sp., and 10 strains of Vibrio cholerae. Phage isolates were grouped by plaque morphology and representative morphotypes were characterised by restriction fragment length polymorphism (RFLP) analysis and Southern blot hybridisation.

Results: Bacteriophage diversity and titers were higher during the beginning of the flood season (June-August) and lower in other months (April, May, and September), indicating that seasonal run-off affects phage diversity and abundance. The 98 phage isolates fell into nine distinct morphotypes designated as coliphage-Dhaka (CPD) 11-19. Host range, RFLP patterns, and the estimated genome size indicated that the morphotypes were distinct except that CPD13 and CPD19 have identical RFLP pattern. Southern blot analysis indicated that all the morphotypes except CPD14 and CPD15 are genetically related. A colony blot hybridisation screening of 500 different colonies of 97 different strains of three different bacterial species indicated that none of the phage isolates is lysogenic. Lytic infection of the 87 bacterial strains indicated that most morphotypes have a limited host range except CPD12 and CPD15. These two morphotypes infected and lysed 30-70% of the test bacterial strains.

Conclusions: Of the nine coliphage morphotypes characterised in this study, CPD12 and CPD15 have the potentials for developing therapeutic phage strains.