BACTERIOPHAGE THERAPY ON Pseudomonas aeruginosa

Introduction
Bacteriophages are viruses that infect bacteria and replicate within the bacterial cell wall. Most have double-stranded DNA genomes found in heads
with icosahedral symmetry, and their tails vary in length. All bacteriophages are classified in the order Caudovirales and belong to the families Myoviridae (long, contractile tail), Siphoviridae (long, non-contractile tail) and Podoviridae (short, non-contractile tail) (Harper & Enright, 2011). Bacteriophages were first discovered by Fredrick Twort and Felix D’Herelle in 1915. Since then, bacteriophages started being widely used for treating bacterial infections. This, however, did not last long as chemical antibiotics were discovered and preferred because bacteriophages were not well understood and their efficacy was controversial. Things have now changed due to the development of antibiotic-resistant bacterial strains and bacteriophages have started being used again.
Pseudomonas aeruginosa is a multidrug-resistant Gram-negative bacteria that causes infections in the lungs of cystic fibrosis patients and is a regular cause of hospital-acquired bacterial pneumonia and ventilator-associated pneumonia. Since bacteriophages are capable of reaching bacteria protected within biofilms (such as those found in the lungs of patients with cystic fibrosis), they are being considered as an alternative treatment to antibiotics.
Types of P.aeruginosa bacteriophages
  Many P.aeruginosa bacteriophages have been discovered, and they are classified into at least  seven genera of lytic phages. These include T7-like, ɸKMV-like, LUZ24- like, N4-like, PB1-like, ɸKZ-like and JG004-like including a similar number of temperate genera.(Essoh et al., 2013).  Therapeutic bacteriophage cocktails such as “pyophage” have also been formulated. “Pyophage” contains many different phages that target streptococcus, staphylococcus, Escherichia coli, proteus and P. aeruginosa.
In- vitro and In- vivo Phage Trials
Many in-vitro and in-vivo phage trials have been conducted on animal models and human patients. In in-vitro trials, the potential of phages against P. aeruginosa strains in planktonic cultures or biofilms isolates has been evaluated. Some of the trials that have been done include: (1.) Fu et al. study of the effect of lytic phages in the prevention of P. aeruginosa biofilm formation in hydrogel-coated catheters, (2.) Pires et al.  study of biofilm control using a broad- host- range phage for P. aeruginosa, (3.) Torres-Barceló et al. report on treatment using a combination of Podoviridae phage LUZ7 and streptomycin against P. aeruginosa PAO1 (Pires, Vilas Boas, Sillankorva, & Azeredo, 2015).
 Some of the in- vivo trials that have been conducted on human patients include: (1.) Wright et al. study of the the efficacy and safety of a therapeutic phage preparation (Biophage-PA), (2.) Sivera Marza et al. report on the successful topical use of phage to treat a burn patient who had been colonized by P. aeruginosa months after skin grafts had been applied and (3.) Merabishvili et al. description of a quality-controlled small-scale production of a phage cocktail (BFC-1) for use in human clinical practice(Pires et al., 2015).
Discussion
Many bacteriophages have been isolated and their effects against P. aeruginosa documented. A cocktail of  ɸMR299-2 and ɸNH-4 was effective in eliminating P. aeruginosa NH57388A (mucoid) and P. aeruginosa MR299 (non- mucoid) strains when growing as a biofilm on a cystic fibrosis bronchial epithelial CFBE41o- cell line (Alemayehu et al., 2012). PAK-P or P3-CHA reduced mortality and lung damage in mice with lethal pneumonia caused by MDR P. aeruginosa (Rolain, Hraiech, & Bregeon, 2015). Cocktail from “pyophage” showed lytic activity against 70% of P. aeruginosa strains cultured in growth medium, while PAK-P1 reduced mortality and lung inflation in mice with lethal pneumonia caused by PAK bioluminescent P. aeruginosa strain. Phage LUZ7 used with streptomycin inhibited growth of the P. aeruginosa PAOI strain, while Engineered T7 phage with aiiA gene inhibited biofilm formation in the P. aeruginosa PAOI strain. Phage PB-1 and tobramycin reduced resistance to tobramycin in the P. aeruginosa PAOI strain (Rolain et al., 2015). Phage P2-10Ab01 isolated from sewage water in Abidjan could lyse two pyophage-resistant strains, C7-6 and C9-5, and PAP3 was capable of lysogenization (Essoh et al., 2013).
Quorum Sensing Inhibition
Since hydrolyzing acyl homoserine lactonases can decrease in vivo virulence of P. aeruginosa and in vitro biofilm production, bacteriophages can be modified genetically to produce lactonase, which would facilitate inhibition of  P.aeruginosa biofilm production (Rolain et al., 2015). …
Mechanism of Bacteriophage Resistance
Even though bacteriophage therapy has made headway in the treatment of bacterial infections, the issue of bacteria that are resistant to phages has come up. The mechanisms of bacterial resistance to phages drive the evolution of both bacteria and bacteriophages, and ongoing isolation of new bacteriophages targeting various hosts and host receptors is, therefore, necessary. Bacterial resistance to phages may involve three mechanisms: inhibition of the adsorption of phages on the bacteria and injection of DNA, use of restriction enzymes to degrade phage DNA and the CRISPR- Cas system that gives bacteria immunity against the phages (Essoh et al., 2013). The CRISPR-Cas mediates interference against certain types of temperate phages. However, some phages found in the Mu- like genus have been found to carry genes that can inactivate the system.
Challenges Facing Use of Bactereophages
The potential disadvantages of bacteriophages  can be categorized into four: phage selection, phage-host- range limitation uniqueness of phages as pharmaceuticals and unfamiliarity with phages (Loc-Carrillo & Abedon, 2011). Not all phages are good for therapeutics since some of them may cause the development of immunogenic reactions due to large uncontrolled amounts of phages in circulation (Paul et al., 2011). However, use of bacteriophages devoid of endotoxins should not induce a strong stimulation of the pro-inflammatory markers (Morello et al., 2011).
Conclusion
In this therapy, isolation of bacteriophage using the strain from the patient is preferred over using readymade phages (Henry, Lavigne, & Debarbieux, 2013).  Moreover, bioluminescent bacteria can be used to compare several bacteriophages, so as to establish candidates for therapeutics based on their real in vivo efficacy instead of they are in vitro performance (Debarbieux et al., 2010).  With a combination of proper selection of phages, proper formulation and improved clinical understanding of how phages work, bacteriophage could easily become the most effective way for treating bacterial infections.
References
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Rolain, J.-M., Hraiech, S., & Bregeon, F. (2015). Bacteriophage-based therapy in cystic fibrosis-associated Pseudomonas aeruginosa infections: rationale and current status. Drug Design, Development and Therapy, Volume 9, 3653. http://doi.org/10.2147/DDDT.S53123