Exploitation of Bacteriophages in Various Water Systems

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Water Systems (river, lake, pond, and swimming tanks) containing diverse group of pathogenic bacteria, viruses, protozoa and metazoan parasites, even when treated with chemical agents, continue to create serious health problems. Radiation, one of the most efficient water treatment procedures, is very expensive for practical implementation, in case of developing countries. Alternatives such as biocontrol agents may prove effective at such levels. There are reports in which phages have been used to control pathogens in aqueous environment, In vitro . EPA (Environmental Protection Agency) worst case water (WCW) microcosm studies were carried out for testing biocontrol of Salmonella species with the help of bacteriophages. The WCW provided a consistent and relatively simple, defined, turbid, aqueous matrix, containing high total organic carbon (TOC) and total dissolved solids (TDS) to simulate swine lagoon effluent. Wells containing WCW were loaded with Salmonella enterica subsp. enteric serrovar typhimurium (ATCC14028) and then treated with phages alone and in cocktail combinations. These treatments showed high inactiva-tion rate of Salmonella group (McLaughlin and Brooks 2008). In another study river water microcosms were used in plates for testing potential of coliphages and phages specific for staphylococcus aureus against E. coli and Staphylococcus aureus (Bahadoor 2005). According to Withey et al. (2005), phages have the ability to control environmental waste water process problems such as foaming in activated sludge plant, sludge dewaterability and digestibility.

In the central part of Japan, fate of coliphages in the waste water treatment processes was studied for 10 months. High titer of coliphages (ten times greater than the influent) was detected in the effluent. Bacteriophages have the potential to reduce competition between nuisance bacteria and functionally important microbial populations. Phages are natural predators of bacteria. They are specific and precise in their action of predation. The specificity of interaction between phage attachment structures and host cell surface receptors influences bacterial host range. Host range is generally assumed to be narrow for aquatic phages (Alonso et al. 2002). However broad host range (polyvalent) Cyanophages are widely isolated (Suttle 2000) . Such polyvalent phages have been isolated from sewage treatment plants (Jensen et al. 1998) . Lytic phages are commercially important in terms of their bacteria killing activity. Lysogenic or temperate phages are not much important commercially; but they do posses research importance in terms of their capacity to integrate their genome into host genome and reside in the host genome in the form of prophage.

Constructed wetland system with bacteriophage application offers attractive alternate for storm water management for reducing load of disease causing viruses to the receiving waters (Yousefi et al. 2004). Bacteriophages were used to decrease the bacterial load from sewage water along with the self purification level in the rivers and lakes (Pretorius 1962). Bacterial contamination of industrial water systems leads to biofouling by biofilms and corrosion from bacterial induced corrosion. Prevention or reduction of process interruptions and general contamination, fouling and corrosion is achieved by the destruction of targeted problematic bacteria with naturally occurring, non-engineered bacteriophage virulent for targeted bacteria. The use of bacteriophage therapy in aquaculture seems very promising and practical. Few attempts have been made to use bacteriophages to treat diseases in aquaculture. Wu and Chao (1982) examined the effect of a phage, FET-1, isolated from pond water in Taiwan, on Edwardsiella tarda. In in-vitro experiments, phage killed 25 of 27 E. tarda strains and reduced the bacterial count to less than 0.1% when a bacterial suspension of 1.2 x 10 1 2 cells/ml was infected with FET-1 at multiplicity of infection (MOI) of 0.08 after 8 h.

The studies of Park et al. (1997) and Nakai et al. (1999) have shown that bacteriophage could be used to control Lactococcus garvieae infections of yellowtail and other marine fishes.

Use of phages in water treatment processes is very important due to their predation power, and their ability of not being pathogenic or toxic to humans. Specific bacteriophages such as Salmonella spp. phages or Vibrio spp. phages can be used to remove these pathogens from waste water (Shah et al. 2005; McLaughlin et al. 2006). To understand the scope of phages in waste water treatment processes, it is important to understand the phage and bacterial host relationship. Most of the bacterial strains present in the environment are ever emerging as antibiotic resistant strains during the course of evolution through mutation and conjugation. Such highly pathogenic and resistant bacterial strains can not be easily removed using traditional chemical disinfection process. Also, due to repeated use of chemical disinfectants, chlorine resistant and chlorine degrading bacteria are emerging. Hence for successful application of phages in waste water treatment, it is of prime importance to know the killing power and the ways in which phages can be applied for disinfection.

Phages have been applied almost in all fields to kill nuisance bacteria. Bacterial strains associated with waste water and chlorinated drinking water contains coli-forms, enteric pathogens including Vibrio spp., Salmonella spp., Shigella spp. etc. Pathogens are found to have strong ability to persistently adapt to surrounding conditions for survival (Kearney et al. 1994). Hence they can be relatively resistant to traditional methods of pathogen removal. Members of the genus Salmonella are known to survive for more than 1 year in the sludge applied to farm land (Mitscherlich and Morth 1984; Edmonds 1976). The bacteria survived upto 16 months on grass treated with sludge in Switzerland (Hess and Breer 1975). It is known that most of the Salmonella spp. are resistant to amphicillin, chloramphenicol, and other classes of antibiotics. These strains have been isolated (Kare et al. 1999; Salehi et al. 2005; Murugkar et al. 2002). It has also been found that Salmonella typhimurium can grow at pH 4.0 (Lin et al. 1995; Foster and Spector 1995). Similar observations are noted with Shigella spp. and E. coli spp. (Lin et al. 1995). It shows that, contaminated water associated bacteria have an efficient adoptive behavior against environmental conditions. Vibrio spp. is one of the most notorious and highly pathogenic bacterium found in the contaminated water. Vibrio cholera responsible for cholera is highly prevalent in estuarine conditions and is related to cholera outbreaks in developing countries, most notably in Bangladesh (Alam et al. 2006).These strains of Vibrio are highly pathogenic and frequently mutate to give rise to new antibiotic resistant and toxic strains. In one study, it has been found that cholera epidemics are self limiting in nature due to phage mediated biocontrol; which can be said to be related to amplification of Vibrio cholerae specific bacteriophages due to host (Shah et al. 2005).

Major problem regarding phage mediated biocontrol of bacteria is the efficiency of the phage production. Also, the phages on viable but non culturable bacteria have not been evaluated. It has been found that Salmonella spp. exists in stagnant water in dormant form and not in an active form. Most of the phages cannot attack dormant bacteria due to improper adsorption on bacterial surface. One aspect of use of phage is the emergence of bacteriophage insensitive mutants (Connerton and Connerton 2005). However, unlike chemical therapeutic agents such as antibiotics, phages constantly evolve to circumvent their host's defenses and resistant bacteria are often less fit or less virulent than their phage sensitive counter parts (Smith and Huggins 1983).

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