. Therefore, a different scheme with better discrimination power and better typeability was essential. New phage typing scheme which was developed based upon phages isolated from NICED, Kolkata can distinguish V. cholerae O1 strains into 27 different types and is useful to achieve more type distinction and improved discrimination within the biotype ElTor strains to get a better idea on the origin and clonality route of the outbreak. The present study has shown that type 27 is the dominant phage type in every state with maximum percentage [80%] from West Bengal [Figure 1], indicating the dissemination of cholera outbreak may have occurred from common precursor strain. These observations reveal a common origin and probably the pathogenic strains of cholera belong to the same clone. O1 strains from Maharashtra, Andhra Pradesh and Gujarat exhibited the maximum number of phage types where chorea is endemic over last 5 years. Co-occurrence type 27 and incidence of cholera indicates that V. cholerea O1 strains belonging to phage type 27 might be primarily responsible for outbreaks in recent past in India.
|Figure 1: Distribution of strains belong to phage Type 27 [T-27] in different states of India isolated from 2012 to 2017|
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Apart from the phages characterized in our laboratory to distinguish V. cholerae O1, naturally occurring similar kind of lytic phages may play an essential role in controlling the spread of cholera infection. In the recent past, a model was proposed to understand how equilibrium exists between vibriophages and its host contributing to an outbreak. In an outbreak, increase load of V. cholerae leads to an increase in vibriophage population, which subsequently results in declining of vibrio population and helps in controlling outbreak. A recent study suggests that a cholera patient having vibriophages in their stool less likely to transmit cholera infection through household contact when compared with patients without any vibrophage in their stool. Later it was found that phage positive vibrio samples are non-motile under dark field microscope supporting the role bacteriophages in controlling and spread of an outbreak.
Bacteriophages are a cost effective alternative to antibiotics and sometimes may be used for therapeutic purposes to treat multi drug resistance (MDR) bacteria with limited success.,,,, In India, the history of phage therapy dates back to 1930s when vibriophages had been successfully used to treat cholera infection in the pre-antibiotic era.,,
Phage therapy remained a standard part of the healthcare systems in Eastern Europe and the USSR since the second half of the 20th century. However, it was largely neglected in the other part of the world due to easy availability of antibiotics for treatment. Widespread use of antibiotics resulted in the development of MDR bacteria which is a major problem in healthcare units today. Increase in multidrug resistance phenotype of V. cholerae O1 biotype ElTor makes the population vulnerable to a new pandemic., To overcome the problem of MDR phenotypes of V. cholerae, phage therapy may be a better option. Earlier studies have shown that cocktail of the five bacteriophages reduced the V. cholerae load in a rabbit model of infection when administered 6 or 12 h after the pathogen challenge. In other similar studies virulent vibriophages were used to control diseases in the animal model., We found that typing phages are highly reactive to circulating ElTor strains [Table 2]. Our analysis revealed that the ability of the phages to cause lysis of V.cholerae strains ranges between 80%–94%, signifying their probable usages as candidate for phage cocktail for therapeutic uses. Moreover, as 94% of the circulating strains are susceptible to S5 phage, vibriophage S5 alone may also be used as an ideal candidate for phage therapy. Therefore a cocktail of these vibriophages or vibriophage S5 in combination with lytic phages of other diarrhea causing organisms may be considered as an universal cocktail for the prophylaxis of diarrheal diseases.,,, Hopefully