MIIM - Introduction to Infectious Agents - Week 1

Question 1

How have microorganisms imapcted the world in the past? Describe what this process is known as, and why it is so important.

Answer 1

They allowed the process of nitrogen fixation into the soil. These bacteria can be found on the roots of some pants, such as legumes, and allow them to incorporate nitrogen. Herbivores eat these plants, who are then eaten by carnivores, or die naturally. As they decay, their nitrogen content is once again recycled into the soil, air, or water. This is the nitrogen cycle.

Question 2

Describe nitrogen fixation.

Answer 2

When nitrogen in the air is is fixated into the soil by bacteria.

Question 3

Describe ammonification.

Answer 3

When decaying organic compunds have their nitrogen content converted to ammonia by decomposers.

Question 4

Describe nitrification.

Answer 4

The process by which ammonia in the soil is converted to nitrites and nitrates by nitrifying bacteria.

Question 5

Describe denitrification.

Answer 5

When nitrates are converted to nitrogen gas by denitrifying bacteria.

Question 6

Describe assimilation.

Answer 6

When nitrates are taken up by plant organisms.

Question 7

Where do bacteria sit on the food chain, and how do they support it?

Answer 7

They sit at the bottom, and support the entire chain by providing essential nutrients.

Question 8

How do bacteria support humans?

Answer 8

In the gut, by synthesising essential B vitamins such as thiamine (B1), riboflavin (B2), pantothenic acid (B5), biotin (B7), and folate (B9).

Question 9

Are the majority of microbes good/neutral, or harmful?

Answer 9

Good/neutral. Only a handful are associated with infectious disease.

Question 10

Name the 5 types of infectious agents. Note which are acellular.

Answer 10

Bacteria, fungi, parasites, viruses, and prions.

Viruses and prions are acellular.

Question 11

What is characteristic of prokaryotic organelles vs eukaryotes?

Answer 11

They are free-floating in prokaryotes, and are not membrane-bound, as in eukaryotes.

Question 12

Compare prokaryotic DNA with eukaryotic DNA (2).

Answer 12

Prokaryotic DNA is closed and circular.

Eukaryotic DNA is linear.

Question 13

What ribosome density unit do prkaryotes and eukaryotes have?

Answer 13

Prokaryotes use 70S

Eukaryotes use 80S

Question 14

How do prokaryotes and eukaryotes replicate?

Answer 14

Eukaryotes - mitosis/meiosis

Prokaryotes - binary fission

Question 15

Which of the following are present in prokaryotes?
Endoplasmic reticulum
Peptidoglycan
Plasma membrane sterols

Answer 15

None except peptidoglycans.

Question 16

Describe what is meant by site-specific pathogenicity.

Answer 16

Occurs when bacteria appear neutral or beneficial in one location, but when moved to another region, they are pathogenic.

Question 17

Name 6 factors that can affect a microbiome composition.

Answer 17

Climate/geography
Age
Shared living (family/aged care)
Personal hygiene
Diet
Medical treatment/intervention/hospitalisation

Question 18

What is the periplasmic space?

Answer 18

The space between the cell wall and the inner cell plasma membrane.

Question 19

What confers shape to a bacteria?

Answer 19

Cell wall

Question 20

What term is given to rod-shaped, spherical, and spiral forms of bacteria?

Answer 20

Rods - bacilli
Spherical - cocci
Spiral - spirilla

Question 21

Do all bacteria have cell walls?

Answer 21

No, such as mycoplasma

Question 22

Describe the cell wall layers of gram-positive (3), gram-negative (2), and acid fast bacteria (5).

Answer 22

Gram negative have:
Inner plasma membrane
Thinner peptidoglycan layer
Outer membrane

Gram positive have:
Inner plasma membrane
Thicker peptidoglycan layer

Acid fast have:
Outer lipid layer
Thick mycolic acid layer
Arabinogalactan layer
Thin peptidoglycan layer
Inner plasma membrane

Question 23

What is peptidoglycan also known as, and what 2 subunits are used to form bacterial cell walls?

Answer 23

Murein.

Subunits are N-acetyl muramic acid, and N-acetyl glucosamine.

Question 24

What structure joins chains of peptidoglycan in bacterial cell walls?

Answer 24

A chain of amino acids extending downwards (L-Ala, D-Glu, L-Lys, D-Ala), connected by a penta-glycine bridge (connecting one D-Ala to another L-Lys).

Question 25

What component of the immune system recognises bacterial cell wall components?

Answer 25

Toll-like receptor 2 TLR2

Question 26

Describe the procedure for a gram stain, and what happens to the bacteria in each step.

Answer 26

-A bacterial emulsion is placed on a slide, and allowed to air-dry if neccessary.
-The slide is heatfixed using a flame to fix and kill the bacteria.
-Crystal violet is applied. It stains everything purple.
Iiodine is added as a mordant, and complexes with the crystal violet to prevent it from being removed in the next step.
-Acetone/alcohol is used as a decolouriser to remove crystal violet.
-Dilute carbol fuchsin is used as a counterstain to stain everything pink.
-The slide is washed a final time with water and allowed to air-dry.

Question 27

Describe how gram-positive and negative bacteria stain with a gram stain, and why this is the case.

Answer 27

Positive - purple
Negative - pink
Iodine binds with crystal violet to prevent it from exiting a bacterial cell. This only applies to gram-positive bacteria due to their large peptidoglycan layer.
Gram-negative bacteria have a thinner peptidoglycan layer, and thus the crystal violet is removed with the decolouriser, and counterstained with catbol fuchsin.

Question 28

Describe a benefit of gram-positive bacteria having a thick peptidoglycan layer.

Answer 28

Resistance to drying and disinfectants.

Question 29

Describe a benefit of gram-positive bacteria having a thinner peptidoglycan layer and outer membrane.

Answer 29

The periplasmic space is the site for many specialised proteins, and the outer membrane allows resistance to antibiotics.

Question 30

What are plasmids?

Answer 30

Circular DNA that form extra genes and are transferrable.

Question 31

What are flagella?

Answer 31

Confers motility by rotating.

Question 32

What are pilli and fimbriae?

Answer 32

Pili allows conjugation

Fimbriae allows adhesion

Question 33

What is a bacterial capsule, what is it composed of, what does it aid in, and how does it affect recognition by the immune system?

Answer 33

Usually is a secretion of polysaccharides.

It can aid in adhesion, and masks immunogenic structures, evading the immune system.

Question 34

Describe a bioflim.

Answer 34

Biofilms result when capsule secretions are less structured, and can result in a slime or biofilm layer.
They are large hydrogel ECM in which bacteria replicate and signal to one another.

Question 35

How do bacteria signal within a biofilm?

Answer 35

Quorum sensing

Question 36

Describe endospores.

Answer 36

When environmental conditions become difficult, all the essential components of the bacteria such as the DNA and ribosomes are packaged into an endospore. The rest of the cell bursts open and releases the endospore, which is extremely resistant to sterilisation and heat.

Question 37

Name the 3 types of bacteria by their metabolism. Describe why they are so.

Answer 37

Obligate anaerobes - cannot tolerate oxygen gas. The end-products of aerobic metabolism is toxic to them, such as hydrogen peroxides and superoxides. They lack the enzymes to deal with these.

Aerotolerant anaerobes - can tolerate, but do not use oxygen gas, as they have the appropriate enzymes to deal with the peroxide/superoxides.

Facultative anaerobes - can grow aerobically or anaerobically.

Question 38

Describe the 4 phases of bacterial growth as seen in a lab.

Answer 38

Lag phase - flat line at the beginning in which the bacteria are preparing to grow in their medium. Their numbers are doubling every cycle.
Logarithmic phase - as bacterial numbers double per cycle, their numbers grow rapidly, and on a log-curve, this appears as a linear line.
Plateau - bacterial numbers slow and eventually plateau due to the low availability of nutrients or space.
Decline - bacterial numbers begin to decrease due to depleted nutrients, space, or accumulation of toxic metabolic end-products.

Question 39

Describe briefly how a MALDI-TOF can be used as an automated identification system for bacteria.

Answer 39

A series of 96 wells are placed underneath a mass-spectrometer. Each well is sequentially ionised, which is then read by the spectrometer.
Each species of bacteria will have its unique pattern on the readout, which can be compared to a central database for quick identification.
Building this central database in the first place will require manual purification of bacterial colonies in order to obtain individual unique patterns.

Question 40

Are viruses considered living?

Answer 40

No

Question 41

What kind of genetic material can viruses contain (4)?

Answer 41

dd or ss DNA/RNA

Question 42

Are viral nucleic acids linear or circular?

Answer 42

Can be linear or circular.

Question 43

Do viruses always have a capsid or envelope?

Answer 43

Not always, they can be a naked piece of nucleic acid

Question 44

What can persistent viral infections cause?

Answer 44

Cancer

Question 45

Whar do enveloped viruses do to tner a membrane?

Answer 45

They first fuse with the target membrane.

Once theyve replicated, new viruses bud off the infected cell.

Question 46

Do fungi reproduce sexually or asexually?

Answer 46

Both

Question 47

What are fungal infections typically associated with?

Answer 47

Contact lens wear.

Question 48

How can prion diseases spread in an ophthalmic context?

Answer 48

Very rarely through conreal transplant