Chp 7 Part 3

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What is a bacteriophage?

• Virus that only infects bacteria & replicates w/in it

• Parasitize every known bacterial species

• Some bacteriophages make the bacteria they infect more pathogenic

  • bc when they inject their genes into bacteria it causes bacteria to produce enzymes & toxins that aid in virus’ invasion or helps virus evade host’s immune system

T or F: Bacteriophages parasitize every known bacterial species.

TGrue

Bacteriophages recognize and bind to ____________ on the surface of _________ cells.

Bacteriophages recognize and bind to specific receptors on the surface of bacterial cells.

T or F: In order for a bacteriophage to attach to a host cell, the host cell must be compatible w/ the phage’s specificity.

True

T or F: Bacteriophages are estimated to be the most abundant biological entity on Earth (~10 ^ 31), meaning there are more bacteriophages on Earth than all other organisms combined.

True

Explain why bacteriophages are considered “kind of” ubiquitous.

• Bacteriophages are considered “kind of” ubiquitous bc they are essentially found anywhere where bacteria exist.

• Since bacteria are ubiquitous that makes them ubiquitous too.

• Commonly found in: 

  • Soil 

  • Freshwater/oceans

  • Sewage/wastewater

  • Deep Earth crust (i.e. subterranean environments) 

  • Human/animal intestines & other organs/tissues

T or F: Bacteriophages are complex viruses.

True

Briefly describe the structures of a complex bacteriophage.

• Genome: DNA or RNA inside a polyhedral head.

• Sheath: Connects head to tail fibers.

• Tail fibers and pins: Attach to specific receptors on bacterial surface.

What does host specificity mean in bacteriophages, and why can't they infect humans?

• Each phage targets specific bacterial species based on surface receptors.

• This is called host specificity.

• Phages cannot infect humans — even though we have bacteria — because they’re naturally or engineered to target specific pathogens (e.g., Listeria monocytogenes).

• Human cells lack the receptors phages recognize.

T or F: The FDA (Food & Drug Administration) and USDA (U.S. Department of Agriculture) have approved several bacteriophage-based products.

True

Provide descriptions of 2 applications of phages in the food industry.

1. Remediation of Food Processing Plants

• Phage sprays are used on contaminated surfaces (e.g., conveyor belts, cutting tables).

• Targets pathogenic bacteria without damaging equipment or irritating workers.

2. Food Additives for Ready-to-Eat Meats

• Phages added to deli meats, poultry, and cheese to prevent growth of bacteria

  • E.g. Listeria monocytogenes → causes Listeriosis, a serious infection especially dangerous for pregnant individuals, elderly, and immunocompromised.

• Phages sprayed on ground beef used in burgers to reduce:

  • E. coli O157:H7 → causes bloody diarrhea, and can lead to hemolytic uremic syndrome (HUS).

T or F: Phages are used an alternative to chemical disinfectants or antibiotics.

True

Phage Therapy

Genetically modifying bacteriophages and using them to target specific pathogens (cause no harm to beneficial human flora).

Which US agencies have approved phage products for food safety use?

FDA (Food and Drug Administration)

USDA (U.S. Department of Agriculture)

What are FDA/USDA-approved phage products used for? 

• Decontaminating surfaces used for food processing/preparation

• Spraying on meats to control growth of pathogens (e.g. Listeria monocytogenes —> causes listeriosis) 

Which 2 pathogens are most commonly targeted by phage sprays on meat? 

Listeria monocytogenes —> causes listeriosis 

E.coli-0157 —> causes bloody diarrhea

How do phage products benefit the environment and humans?

Serve as alternatives to…

• Chemical disinfectants —> reducing chemical use/irritation

• Antibiotics —> avoiding antibiotic resistance risks

What is the advantage of genetically modified phage therapy?

It targets specific bacterial pathogens only, leaving beneficial human flora unharmed.

Lysogenic Conversion

(a) What is it? 

(b) Mechanism

(a) What is it? 

• Bacteriophage integrates its DNA into a bacterial chromosome

• This gives the bacterium new genetic traits that may code for toxins or enzymes that enhance bacterial virulence

(b) Mechanism

• Temperate phage inserts its genome into bacterial DNA —> forming a prophage

• Bacterium is now carrying the prophage causing it to express new virulence factors —> increasing its pathogenicity

Give an example of a disease caused by lysogenic conversion.

Disease ——> Toxin

• Vibrio cholerae ——> Cholera toxin

• Clostridium botulinum —-→ Botulism toxin

• Corynebacterium diphtheriae ——> Diphtheria toxin

Vibrio cholerae

(a) What bacteriophage infects Vibrio cholerae?

(b) What gene does this bacteriophage carry?

(c) What symptoms does this condition cause? 

(a) What bacteriophage infects Vibrio cholerae?

CTX bacteriophage

(b) What gene does this bacteriophage carry? What role does this gene play in causing disease?

CTX gene which codes for cholera toxin

(c) What symptoms does this condition cause? 

Severe watery diarrhea known as “rice water stools”

T or F: Vibrio cholerae becomes virulent only after infection by the CTX bacteriophage.

True

T or F: A bacteriophage infection can turn a harmless bacterium into a pathogen.

True —> Example is Vibrio cholerae & CTX phacage

Only name the 2 types of bacteriophage life cycles.

(*do not describe)

1. Lytic Cycle (or Lytic Phase)

2. Lysogenic Cycle (or Lysogenic Phase)

Lytic Cycle

(a) Describe what it is and its purpose  in 1 sentence.

(b) Describe the steps.

Changes in Viral Genome & Infectivity

(a) Viral genomes change over time due to which 2 factors? Briefly explain what each factor means.

(b) How can these factors impact viruses?

(a) Viral genomes change over time due to…

1. Mutations: Permanent change in DNA sequence of organism’s genome

2. Reassortment: Exchange of genetics b/w diff strains of same viral species)

(b) Mutations & reassortment impact viruses in the following ways:

• Host range —> can increase/decrease the number of species that virus can infect

• Tropism —> can expand/decrease variety of cell types virus can infect in host

• Transmissibility —> can increase/decrease how easily virus can enter host’s body

• Immune Evasion —> can increase/decrease viruses’ ability to escape host cell immune detection (antibodies) bc of changes in surface proteins 

Name, describe, and compare the types of mutation effects.

Provide a brief example of the impact each type may have.

Type	Effect on Virus	Example Impact
Neutral	No change in fitness.	Silent mutation.
Beneficial	Increases fitness.	Escape immune detection, broaden host range/tropism.
Deleterious	Reduces replication or transmissibility.	Weak or defective viruses.

Tropism

The ability of a pathogen to infect a specific cell/tissue/organ type in host.