Bacteriophages & Its classification, cycles, therapy, and applications

These slides are covering multiple aspects of Bacteriophages including History
Classification
Replication
Plaque Assay
Transduction
Phage Therapy and pahge types.

1. Bacteriophages By: Zoqia Tariq and group University of Gujrat

2. Contents Introduction History Classification Replication Plaque Assay Transduction Phage Therapy

3. Definition A  bacteriophage   (informally,  phage) is a  virus  that infects and replicates within a  bacterium. The term is derived from "bacteria" and the  Greek word   phagein , "to devour".

4. Structure of Bacteriophage .

5. History In 1896,  Ernest Hanbury Hankin  reported that something in the waters of the  Ganges  and  Yamuna  rivers in India had marked antibacterial action against cholera and could pass through a very fine porcelain filter.  In 1915, British bacteriologist  Frederick Twort , superintendent of the Brown Institution of London, discovered a small agent that infected and killed bacteria

6. Classification and Composition of bacteriophages At present over 5000 bacteriophages have been studied by electron microscopy and can be divided into 13 virus families.

7. Genome structure 15091560-052 They all contain nucleic acid and protein. Depending upon the phage, necleic acid can be either DNA or RNA but not both. The nucleic acid of phages often contain unusual or modified bases which protect phage nucleic acid from nucleases that break down host nucleic acids during phage infection. Simple phages may have 2 to 5 genes while complex phages may have over 100 genes.

8. Genome Structure Head, capsid , tail fiber etc .

9. Replication Bacteriophages may have a  lytic cycle or a lysogenic cycle, and a few viruses are capable of carrying out both. Lytic Cycle : bacterial cells are broken open and destroyed after immediate replication of the virion . In contrast, the  lysogenic cycle  does not result in immediate lysing of the host cell. Those phages able to undergo lysogeny are known as temperate phages. Their viral genome will integrate with host DNA and replicate along with it relatively harmlessly, or may even become established as a plasmid.

10. Replication Adsorption or Attachment The lytic cycle begins with a collision between T-phage virion and a susceptible host cell i.e. Escherichia coli. The process of attachment of a virion on the host cell surface is called adsorption.

11. Continue Penetration or Injection The tail fibers of virion bend to bring the spikes and basal plate in contact with the surface of bacterial wall. The tail sheath contracts so that the hollow tail core (inner tube) penetrates the bacterial wall and injects the viral genome into the cytoplasm.

12. Continue Synthesis of proteins and nucleic acid Within minutes, bacterial  ribosomes  start translating viral mRNA into protein. For RNA-based phages, RNA replicase  is synthesized early in the process. Proteins modify the bacterial RNA polymerase so it preferentially transcribes viral mRNA.

13. Conti,… Virion assembly and Maturation The capsid proteins assemble to form empty head and a condensed viral DNA is packed inside it. Finally the separately assembled tail joins to head to form a daughter or progeny virion . Bacteriophage components assemble and phages fully develop. The whole process takes about 15 minutes.

14. Conti,...

15. Continue,… Release of virions During assembly of progeny virions, the bacterial cell becomes spherical. The phage enzymes weaken the cell wall which ultimately burst or lyse to release about 100-200 progeny virions.

16. Continue,… Lysogenic Cycle: The phages that exhibit lysogenic cycle are called temperate phages or non-virulent phages. For example, λ phages attacking E. coli, during lysogenic cycle, the phage DNA integrates into the bacterial DNA and is now called as prophage . The host bacterium containing prophage is called a lysogenic bacterium or lysogen .

17. Replication overview Lytic and Lysogenic Cycle of a bacteriophage

18. Plaque Assay The plaque assay, routinely used for determinations, invaluable in quantitative analysis during mutational and recombinational studies of bacteriophages . During infection of bacteria, enormous quantities of bacteriophages may be obtained for investigation. Often, more than 10 - 10 viruses are produced per milliliter of culture medium.

19. Plaque Assay .

20. Transduction A process by which a virus transfers genetic material from one bacterium to another. Viruses called bacteriophages are able to infect bacterial cells and use them as hosts to make more viruses. After multiplying, these viruses assemble and occasionally remove a portion of the host cell's bacterial DNA. Later, when one of these bacteriophages infects a new host cell, this piece of bacterial DNA may be incorporated into the genome of the new host .

21. Types of Transduction There are two types of transduction: G eneralized S pecialized In generalized transduction, the bacteriophages can pick up any portion of the host's genome. In specialized transduction, the bacteriophages pick up only specific portions of the host's DNA. Scientists have taken advantage of the transduction process to stably introduce genes of interest into various host cells using viruses.

22. Transduction Generalized transduction

23. What is phage therapy? Phage therapy is the therapeutic use of bacteriophages in order to treat pathogenic bacterial infections This method is still used for the treatment of a variety of bacterial and poly-microbial biofilm infections But it has not yet been approved in Georgia It has many applications in human medicine as well as dentistry, veterinary science, and agriculture Bacteriophages are more specific than antibiotics. They have a high therapeutic index Now-a-days phages are also used to kill food poisoing bacteria e.g Listeria.

24. Use of phage therapy in history Previously, phage therapy was used to treat Anthrax Bubonic plague Cholera Dysentery Enteritis Gas gangerene Gastrointestinal infections Gonorrhea

25. Continued ... Meningitis Staphylococcal skin diseases e.g. boils, carbuncles, furuncles etc. Tuberculosis Thyroid fever Lung and upper respiratory tract infections Several bacterial infections e.g. mastoid infections, vaginitis etc.

26. Advantages Of Phage Therapy Over Antibiotics Phage therapy is effective against multidrug-resistant pathogenic bacteria It has high specificity to target only bacterial species It can rapidly respond to appearances of phage resistant mutants. The cost of developing a phage system is cheaper than developing a new antibiotic Unlike antibiotics, side effects are uncommon because phages as well as their products do not effect eukaryotic cells. They also replicate at the site of infection

27. Use Of Phage Therapy In Food Industary Phage therapy controls the growth of Campylobacter and Salmonella on chicken skin, Samonella eneritidis in cheese, Listeria monocytogenes on meat and on fresh-cut fruits It controls the presence of biofilms in food processing environments i.e used to control the growth of L. Monocytogenes Hence, useful to provide hygeinic foods including meat and poultry products.

28. Phage Therapy In Agriculture And Fisheries Phage therapy controls the fish pathogens It is used in food and livestock markets in order to avoid contamination of food products with pathogenic bacteria like L. Monocytogenes , Salmonella on cut vegetables and fruits and the pathogenic Escherichia coli O157 : H7.

29. 15091560-054 Advantages of bacteriophages Phages can be used as bio control agents in agriculture and petroleum industry . Phages are used as vehicles for vaccines both DNA and protein, for the detection of pathogenic bacterial strain, as display system for many proteins and antibodies . Bacteriophages are diverse group of viruses which are easily manipulated and therefore they have potential uses in biotechnology, research, and therapeutics.  They have been proposed as alternatives to antibiotics for many antibiotic resistant bacterial strains.  Phages are very specific and do not harm the useful bacteria that live in and on the body.

30. Continued… Phages are also excellent as food   bio preservation  agents since they are reported to lyse hosts at temperatures as low as 1°C, limiting growth of pathogenic and spoilage bacteria on refrigerated foods. Reduction of colonization on foods ( bio control ) during industrial food processing can be accomplished by applying phages directly on food surfaces. Application of phages to poultry has been successful to prevent fatal respiratory infections in broiler chickens. Phages can be administered orally, incorporated in drinking water or food to control  Salmonella and Campylobacter in poultry, or by spray to target avian pathogenic E. coli in poultry 

31. Disadvantages of Bacteriophages There are no internationally recognized studies that prove the efficacy of phages in humans . Bacteria can also become resistant to phages . Bacteria have a type of ‘immune system’ that destroys the hereditary material of some penetrating phages. Only suitable phages can conquer this ‘immune system. Infections whose agents are hidden in the interior of human cells may be inaccessible to phages. Phages are more difficult to administer than antibiotics. A physician needs special training in order to correctly prescribe and use phages . In comparison to chemical molecules, phages are complex organisms that can transfer toxin genes between bacteria.

32. Continued… Phages that are injected into the bloodstream are recognized by the human immune system. Some of them are quickly excreted and, after a certain period, antibodies against the phages are produced by the body. For this reason, it appears that one type of phage can only be used once for intravenous treatment. In comparison to chemical molecules, phages are relatively large. For this reason, the sites in the body that can be reached by them must be carefully clarified.

33. Viroids and Prions: Viruses, viroids , and prions are all a cellular pathogens. They are not within any kingdom and carry their own significant characteristics. Obligate intracellular parasite – require a host to cause damage Filterable – small enough to be filtrated Contains an outer protein coat and inner genome Has only one kind of nucleic acid (RNA or DNA, but never both) Lacks metabolic abilities

34. Continued… Viroids: These are very small, circular RNA (may appear linear), and infectious in plants. They do not contain a capsid . A virion contains a protein coating called a  capsid,  which surrounds the core of the virus containing the nucleic acid. Some virions also contain an  envelope  which is made up of a phospholipid membrane. Prions: Prions are proteinaceous infective particles.  Prions do not contain nucleic acid . Prions infect animals and is responsible for a number of diseases that affect the brain and other neural tissue

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