30.2 Pathogenic Organisms

Question 1

How many human and bacterial cells do we have in us?

Answer 1

• Human -> 10¹³
• Bacterial -> 10¹⁴

Question 2

Can all bacteria be Gram stained?

Answer 2

No. For example, Mycobacterium tuberculosis cannot be Gram stained due to the high concentration of mycolic acids in the cell membrane, which makes the bacterium impervious to the stain.

Question 3

Describe the structure of Gram positive bacteria.

Answer 3

Cell wall contains:

• Thick peptidoglycan layer -> Various proteins and teichoic acids within it
• Single membrane on the inside of the peptidocglycan layer

Question 4

Describe the structure of Gram negative bacteria.

Answer 4

Cell wall contains:

• Outer membrane -> Containing lipopolysaccharides (LPS)
• Periplasm (where the peptidoglycan is)
• Inner membrane

Question 5

In what type of bacteria are lipopolysaccharides found and how?

Answer 5

• In Gram-negative bacteria
• The lipid portion is embedded in the outer membrane, while the polysaccharide chains extend outwards

Question 6

What are the main differences between Gram-positive and Gram-negative bacteria?

Answer 6

Question 7

What are the 4 main categories of bacteria?

Answer 7

• Pyogenic bacteria (pus-forming)
• Enteric bacteria (Found in the intestines of animals)
• Exotoxin producers
• Facultative intracellular parasites

Question 8

Give examples of exotoxins and their mechanism of action

Answer 8

*Cholera toxin - binds to GM1 gangliosides on intestinal epithelial cells ->activate adenyl cyclase -> increased cAMP -> increased Cl- channel opening -> loss of Na+/ H20 -> diarrhoea.
*Diphtheria toxin - inhibits protein synthesis -> cell death.
*Tetanus toxin - cleaves synaptobrevin preventing release of inhibitory NTs (glycine and GABA) from presynaptic vesicles -> unopposed muscle contraction and spastic paralysis

Question 9

What is the difference between facultative + obligate IC parasites?

Answer 9

Facultative intracellular parasites (e.g. Shigella) are capable of living and reproducing in or outside of host cells. Obligate intracellular parasites, on the other hand, need a host cell to live and reproduce.

Question 10

The difference between Eukaryotic and Prokaryotic cells.

Answer 10

Question 11

Define viruses.

Answer 11

Obligate intracellular parasites which can cause disease by inducing inflammation, causing cell death, and/ or increasing the likelihood that a tumour will develop.

Question 12

Name four species of malaria parasite, and the insect vector

Answer 12

• Plasmodium vivax
• Plasmodium ovale
• Plasmodium malariae
• Plasmodium falciparum
• Vector - female Anopheles mosquito

Question 13

What causes sleeping sickness?

Answer 13

There are 2 forms of HAT (Human African Trypanosomiases) that both cause sleeping sickness.
*T. brucei gambiense causes 92% (WHO, 2023) of the reported cases and causes a chronic illness.
*T. brucei rhodesiense results in a more acute, rapidly progressing disease.

Question 14

Name the insect vector and causative agent (2 species) of visceral leishmaniasis.

Answer 14

• Leishmania donovani and Leishmania infantum
• Vector is the sandfly. Leishmaniasis is transmitted by the bite of an infected female phlebotomine sandfly.

Question 15

What are examples of some conditions caused by fungi?

Answer 15

Athlete’s foot
Thrush
Ringworm

Question 16

What are microbiota?

Answer 16

They are non-pathogenic micro-organisms that are usually harmless and play a role in protection from pathogens.

Question 17

What is the main role of the gut microbiota?

Answer 17

Protects the gut against colonisation by exogenous, pathogenic organisms - by outcompeting them

Question 18

What can cause immunosuppression?

Answer 18

Disease in immunosuppressed individuals, e.g. AIDS, immunosuppression after transplantation, people with inherited defects of the immune system (e.g. primary immune deficiencies).

Question 19

What is a pathogen?

Answer 19

A bacterium, virus or other microorganism that can cause disease. They have evolved specific mechanisms to evade and avoid host defence mechanisms.