Shared Flashcard Set

Details

Bacteriophage
Viruses that attack Bacteria
9
Microbiology
Professional
07/20/2011

Additional Microbiology Flashcards

 


 

Cards

Term

 

 

 

Bacteriophages

Definition
  • Viruses that infect bacteria and require bacterial host for replication

    Obligate intracellular parasites that consist of a protein coat surrounding a central nucleic acid core

    Considerable diversity exists among bacterial viruses in both physical structure and nucleic acid content
Term

 

 

 

Bacteriophages: The Basics

Definition
Tend to have large genomes and complex structure

Most phage are dsDNA viruses but some are ssDNA, ssRNA, or dsRNA

Phage head (protein) contains nucleic acid

Viral ligand that interacts with bacterial receptor located on tail fibers

Sheath (hollow) contracts in some phage during binding to bacterial cell

Most infect by drilling a hole through peptidoglycan and injecting DNA directly into bacterial cell while the rest of the virus stays extracellular

Term

 

 

 

Bacteriophage: Infection

Definition
-Adsorption of the phage to the bacterial cells
-Sheath contraction
-Nucleic acid injection
Term

 

 

 

Phage Multiplication: Lytic 

Definition
-Lytic(replication culminates in lysing and thus killing bacterium)
-Phage takes over host biosynthetic machinery
-Phage mRNAs and proteins produced, sometimes degrading host chromosome
-New phage particles are assembled inside bacterium
-Bacterium lyses due to accumulation of phage lysis protein
-Intracellular phage released; up to 1000 phage/bacterium possible
Term

 

 

 

Phage Multiplication: Lysogenic

Definition
-Lysogenic/temperate (quiescent state in the bacterium such that host is unharmed)
-Phage chromosome circularizes
-Phage-encoded enzyme performs recombination between particular site on circularized phage and particular site on host chromosome– integration of the phage DNA occurs– cell now referred to as lysogen

-Phage genome is repressed by phage-encoded repressor protein
Term

 

 

 

Transduction

Definition
-The transfer of viral or bacterial, or both, DNA from one cell to another via bacteriophage
Term

 

 

 

Mechanisms of Transduction

Definition
Bacterial gene transfer via a virus particle:
-During assembly stage of lytic replication, DNA fragments from host genome are packaged instead of phage DNA  (GENERALIZED)
-During excision of prophage, fragment of chromosomal DNA can be excised with phage DNA (SPECIALIZED)

Lysogenic conversion: Prophage genes (inserted into chromosome) can increase the survival fitness of the host cell in particular situations: 
-Phage repressor and super-infection exclusion provide immunity to the host against lytic infection
-Can convert non-pathogenic bacterial strains into pathogenic ones (encode toxins, for example)
Term

 

 

 

Bacteriophages as Antibiotics?

Definition
Harness the potential of phage to quickly lyse/kill bacterial host

Once it infects its target, it quickly (about 30 min) generates 100s of copies of itself that search out additional microbes to kill

Because phages are ‘living’ organisms (unlike antibiotics), they can evolve as the bacteria evolve; so as bacteria evolve to resist phage, the phage evolves too

Infect only bacteria so they are harmless to mammalian cells and to non-target bacteria (unlike antibiotics), which leaves beneficial gut flora intact

Term

 

 

 

Problems with Phage Therapy

Definition
Because one phage typically infects only one type of bacterium, you must know what a person is infected with prior to treatment and usually need to use a cocktail of phages

Most phages elicit a strong antibody response such that only one treatment will be possible

There is potential to release large quantities of endotoxin from lysed bacterial cells

Most pharmaceutical companies are not interested in investing in clinical trials (very expensive) because they cannot patent the rights to phage therapy (the concept is almost 100 years old)

 


**However, due to emergence of many antibiotic-resistant bugs in recent years, some human phage therapies are becoming available

Supporting users have an ad free experience!