Lecture 12 - Emerging threats and alternative therapies

Question 1

What are some emerging threats (bacteria)

Answer 1

• Yersinia pestis
  
  • Legionella pneumophilia
  • Campylobacter spp.
  • Helicobacter pylori
  • Chlamydia
    Staphylococcus aureus (MRSA)

Question 2

What is yersinia pestis.

Answer 2

Yersinia pestis
Found primarily in wild rodents the plage has three types:
* Pneumonic
* Bubonic
* Septicaemic
Per year 2000-3000 are infected with 182 deaths. It is the most serious bioterrorism threat to the human population (Aerosols/low infective does/person to person spread/availability (nature/collections)/fatal if not treated).

Question 3

Describe legionella pneumophila

Answer 3

Can grow on modified media and is able to avoid host defences by multiplying in phagosome and preventing it from acidifying.

Question 4

Describe campylobacter jejuni

Answer 4

Easily survives in commercial farm settings where the chickens are stressed and have a poor immune system due to being fed antibiotics. It contaminates surfaces in kitchens and can cause huge outbreaks.

Question 5

Why are alternative therapies necessary?

Answer 5

As antibiotics are becoming less effective alternative therapies need to be developed as simply developing new antibiotics is a long process and it would be unethical to stop prescribing them completely.

Question 6

How can bacteriophages be used as an alternative therapy.

Answer 6

Bacteriophages as an alternative therapy
Bacteriophages are viruses that infect bacteria, they are among the most common, most widely distributed and diverse biological entities on earth. Phages are ubiquitous and can be found in all reservoirs populated by bacterial hosts, from soils to the intestines of animals. They enter the cell through the hydrolysis of the peptidoglycan wall.
1. The phage injects phage DNA into the bacteria
2. The phage then circularises
The lytic cycle or lysogenic cycle can then proceed
The lysogenic cycle
The phage DNA integrates into the bacterial chromosome, becoming a prophage.
The bacterium reproduces copying the prophage and transmitting it to daughter cells.
The cell divides produce a population of bacteria infected with the prophage
Occasionally, a prophage exists the bacterial chromosome initiating a lytic cycle
The lytic cycle
New phage DNA and proteins are synthesised and are assembled into phages
The cell lyses releasing the phages

To work as an antibiotic the cycle needs to be lytic

Potential applications for bacteriophages in human health
* Disease therapy
* Drivers of microbiota
* Delivery vectors
* Food safety
* Biomarkers of health/disease
* Reporters of microbiome diversity

Question 7

How is phage therapy used?

Answer 7

Phage therapy is the therapeutic use of lytic bacteriophages to treat pathogenic bacterial infections. The phage however will not replace antibiotics as the first-line, general antibacterial therapy in major western countries. However it has a promising role for phage in situations where antibiotics alone are not sufficient.
Source and propagation:
Isolation involves collecting local samples of water likely to contain high quantities of bacteria and therefore bacteriophages such as sewage or corpses in the case of epidemics (has some ethical issues)
Phage isolation:
The lytic phage are amplified on cultures of the target bacteria, passed through a filter to remove all but the phages.
Phage delivery routes: Parenteral (non-oral), Oral, Local delivery.

Is phage therapy an effective treatment
* Phages have been investigated as a potential means to eliminate pathogens from food.
* Agricultural practice regularly use phages
* It is now accepted by the FDA to kill listeria monocytogenes in cheese.

Question 8

What are the advantages of phage therapy over antibiotics

Answer 8

• Can be verry effective
  
  • When super bacterium appears, the super phage already attacks it. Isolate from the same environment
  • Phages: localised use (penetrate deeper as long as the infection is present
  • The phages stop reproducing once target bacteria are destroyed
    As with antibiotics, bacteria can become resistant to treatments through mutation: however evolution drives the rapid emergence of new phages which means there should be an inexhaustible supply.

Question 9

What are the disadvantages of phage therapy.

Answer 9

• Unlike some antibiotics, phage must be refrigerated
  
  • Doctors need special training
  • Difficulty treating a polymicrobial infection as would need a mixture of phage
  • For best results phage should be tested in the lab prior to application, makes phage less suitable for acute cases where time is not available.
  • Intravenous phage application the phages are recognised by the human immune system and antibodies are produced
  • The high bacterial strain specificity required cocktails for treatment of the same infection as diseases differ from region to region or even person to person.
  • A mixture of phage is often used for efficiency requiring an updated bank of phage.
  • No lytic phage has yet been discovered for clostridium difficile, although temperate phage are known for this species
  • To work, the virus has to reach the site of the bacteria, and viruses do not necessarily reach the same places that antibiotics can reach.
  • The negative public perception of viruses may also play a role in the reluctance to embrace phage therapy.

Question 10

How is manuka honey an alternative treatment?

Answer 10

Manuka honey has antibacterial properties and is effective against 80 microorganisms.
It affects osmolality and peroxide activity. Methylglyoxal is the major antibacterial component
Targets include stress and membrane proteins
Decreases:
* Quorum sensing
* Siderophores
* Surface adhesion
Biofilms:
* Inhibits formation
* Disrupts established biofilms
Inhibits:
* Adhesion to epithelial cells
* Binding to human cells.