specifically in Gangetic Bengal). After several devastating pandemics in the different corners of the globe, the seventh pandemic which originated in Indonesia is still ongoing., Most recent cholera outbreaks caused by V. cholerae O1 occurred in Haiti, causing at least 8,183 deaths and above 665,000 cholera incidences till date (https://www.cdc.gov/cholera/haiti/index.html#two). Global estimates suggest that every year 1.3 million to 4.0 million cases of cholera are responsible for 21,000–143,000 deaths. In India, 27,615 cholera cases were reported between 2010 and 2015, reflecting the sustained presence of V. cholerae O1 in the country and cholera is considered to be one of the underreported pathogens throughout the world.
Several serotypes of V. cholerae strains harbor variety of bacteriophages, and these are beneficial from the clinical viewpoint with the command to control the bacterial population leading to controlling the disease.,, Vibrio phage plays a critical role in the evolution of pathogenic V. cholerae by mediating horizontal transfer of clusters of virulence genes, genomic rearrangements, as well as by bactericidal selection. Lysogenic filamentous phage, CTXϕ, is capable of transferring cholera toxin genes to nontoxigenic strains leading to the conversion of nontoxigenic strains to toxigenic strain.,, The presence of cholera bacteriophages was found inversely associated with the occurrence of viable V. cholerae in the aquatic environment which was found in correlation with the number of locally reported cholera cases. Lysogenic phage present in some environmental V. cholerae strains of both epidemic and nonepidemic serogroups has the power to kill the epidemic strains and thus contributes to the control of the disease.
Different bacteriophages have been used to distinguish pathogenic strains of bacteria from clinical isolates based on their phage susceptibility. Due to their natural specificity, ease of maintenance and straightforward production, phage owns several desirable characteristics which makes them especially suited as bacterial strains discriminator. Since the late 1960s when molecular and modern methods were not widely available, lytic phages of V. cholerae have been used for typing of V. cholerae O1 which remained primary choice for classification of V. cholerae strains. Basu and Mukherjee initially proposed a phage typing scheme for V. cholerae O1 biotype ElTor in 1968, which was considered as a primary choice and a gold standard approach for differentiating V. cholerae biotype ElTor strains in the past. Six phage types were identified by Basu and Mukherjee to characterize V. cholerae O1 biotype ElTor strains, among them phage type 2 and 4 are predominant whereas types 1, 3, 5, and 6 are not in circulation due to some unknown reason, investigation of which may require a separate study. A fundamental feature of the phage typing of V. cholerae was its usefulness in differentiating strains into several types as well as for differentiating classical and ElTor biotypes. Phage typing schemes for V. cholerae O1 and O139 were developed form NICED over the last few decades.,,,
Apart from the importance of cholera bacteriophages to discriminate cholera strains, phages have been used as an alternative to antibiotic therapy to circumvent the burden of antibiotic resistance., An earlier study has found that V. cholerae isolates from Kolkata, India are strongly correlated with resistance to some antibiotics such as streptomycin, tetracycline, and trimethoprim–sulfamethoxazole. Other studies conducted in Nepal on V. cholerae strains isolated from cholera patients have found that 6.45% of the strains were multidrug resistant., These studies suggest that antibiotic-resistant strains of V. cholerae in the Indian subcontinent are on the rise.,, Horizontal gene transfer is an widely accepted methods of antibiotics resistance spreads.
To use bacteriophages for therapeutic application in cholera, phage candidate or phage cocktal must have a broad host range and minimum effect on commensal organisms. A recent epidemi