Isolation and characterization of vibrio cholerae phage from The enviromental waters of the lake victoria region of Kenya

Abstract

The aim of this study was to isolate bacteriophages able to lyse Vibrio cholerae bacteria that cause cholera. Vibriophages have been successfully used to control the pathogen in the environment so as to minimise cholera outbreaks. To isolate bacteriophages lytic against Vibrio cholerae strain used in this study, sixty seven environmental water samples were collected. Forty two samples from the Lake Victoria region of Kenya and twenty five from the Coast region. Sources of the Lake region environmental water samples included ponds, sewage effluent, rivers, wel1s and lakes. Water samples from the coast region were from different rivers. To increase the densities of vibriophages in these environmental water samples, three techniques were employed: filtration, centrifugation and enrichment. Isolation of vibriophages employed the soft agar overlay technique to carry out plaque assays and spot assays. Enrichment procedures were carried out for 48 h in broth containing Vibrio cholerae strain in broth containing at 37°C. The plaques ranged from 16 to 36 pfu/ml after the enrichment process. These plaques were tiny and clear. The spot assays showed a clear zone - at the spot where lysate was spotted either.at !he centre of a lawn of Vibrio cholerae or a t· '''; , streak of the bacterium signifying zones of cell killing which was indicative of the presence of vibriophages in the environmental water samples. A total of 5 samples were positive for plaque assays. To enhance detection of plaques and morphological characterisation of the vibriophages by transmission electron microscopy, reduction of agar concentration from 0.8% to 0.6 % was adopted in this study. MorPhological characterisatio~ of the vibriophages by transmission electron microscopy revealed !heir resemblance to Myoviridae family. The vibriophages had icosahedral shaped head with an average diameter of 88.3nm. A long contractile tail of length and width 84.9nm and 16.1nm respectively. One monograph showed a contracted tail. All these phages belonged to one morphotype. The isolated phage was capable of infecting Vibrio cholerae isolated from the environmental waters of the Lake Victoria region of Kenya. No phages were isolated from the environmental water samples of the coast region. Their host is therefore of considerable ecological interest since it causes cholera especially during heavy rains in Kenya.