Introduction To Microbes

Question 1

What are the 4 main microbes of the microbial world ?

Answer 1

1) viruses
2) bacteria
3) fungi
4) parasites

( in order of size small to big )

Question 2

Which microbe cannot be seen under a light microscope ?

Answer 2

• virus because it is very small - it can only be seen under an electron microscope

Question 3

Describe features of virus

Answer 3

• they do not have a cellular structure
• it consists of either molecules of DNA or RNA - surrounded by a protein coat.
• viruses contain genetic information necessary for directing their own replication of themselves but require the hosts cellular structures to complete the process of their own reproduction.
• the fate of the host cell can include rapid lysis , prolonged release of viral particles ,

Question 4

Describe the structure of the bacteria

Answer 4

1) all bacteria have a cell wall- common feature of the cell wall is the peptidogglycan layer.
2) plasma membrane made out of phospholipids which acts as a physical barrier
3) external to the cell wall may be flagella , pili ( small hairs) and or a capsule( this is a polysaccharide)
4) contains a cytoplasm
5) contains ribosomes
6) contain plasmids which are self replicating molecules that are in control for the development and expression of antibiotic resistance.
7) no nucleus - DNA is free floating

Question 5

What structure of bacteria determines the shape of bacteria ?

Answer 5

Cell wall

Question 6

Are bacteria prokaryotic or eukaryotic ?

Answer 6

Prokaryotic

Question 7

Are fungi eukaryotic or prokaryotic ?

Answer 7

Eukaryotic because they have a nucleus

Question 8

Are viruses eukaryotic or prokaryotic?

Answer 8

Neither - because they lack the characteristics of living organisms. Apart from the fact they can replicate.

Question 9

What is the function of the capsule in some bacteria ?

Answer 9

• capsule allows cells to adhere to surfaces ,protect bacteria from antibodies and phagocytosis

Can act as diffusion barriers against some antibiotics

Question 10

What are the two types of fungi?

Answer 10

1) yeast cells :

2) molds

Question 11

What are the differences between yeast fungi and mould fungi ?

Answer 11

• Yeast fungi are single celled whereas molds are multicellular

Question 12

How do you name bacteria , fungi , parasites ?

Answer 12

• Linnaean taxonomy

- Genus+ species

Question 13

Are parasites eukaryotes or prokaryotic

Answer 13

Eukaryote

Question 14

What are the two types of parasites ?

Answer 14

1) Protozoa

2) helminths ( worms)

Question 15

What are the differences between protozoa and helminths ?

Answer 15

• Protozoa are single celled , whereas helminths are multicellular( worms)

Question 16

What are a few differences between prokaryotes and eukaryotes?

Answer 16

1) . No nucleus in P
2) no membrane bound organelles in P

3) ribosomes are 70S in prokaryotes but 80S in eukaryotes

Question 17

Why do we use gram stains ?

Answer 17

Because unstained bacteria are difficult to detect with the light microscope .

• GRAM stain separates bacteria into two classifications according to their cell wall composition ( gram positive and gram negative )

Question 18

What is a GRAM POSITIVE bacteria ?

Answer 18

• they have a thick , multi layered , peptidogglycan cell wall that are exterior to the cytoplasmic membrane

Peptidoglycan, periplasmic space , plasma membrane

Question 19

What are gram negative bacteria ?

Answer 19

• gram negative bacteria have two membranes - an outer and an inner membrane
• the outer membrane contains the lipopolysaccharide ( the lipid portion is toxic to humans)

Lipopolysaccharide, periplasmic space , peptidoglycan, periplasmic space , plasma membrane

Question 20

Why can the lipopolysaccharide portion of gram negative bacteria be used to identify different stains and species ?

Answer 20

Because it is antigenic

Question 21

Is lipid A ( forms part of the lipopolysaccharide) an endotoxins or exotoxins?

Answer 21

Endotoxins because no substances are secreted .

Question 22

If a microorganism is an ‘aerobe’ what does this suggest ?

Answer 22

• can survive in the presence of oxygen

- an obligate aerobe would mean that it requires oxygen for survival

Question 23

If a microorganism is an ‘anaerobe’ what does this suggest ?

Answer 23

• the microorganism can survive in the absence of oxygen
• an obligate anaerobe would mean that the microorganism requires an oxygen free environment for survival ( unless it is able to form spores)

Question 24

What are the two mechanisms of bacterial pathogens is ?

Answer 24

1) virulence factors

2) toxins

Question 25

Define virulence factors ?

Answer 25

Virulence factors are the genetic , biochemical or structural features that enable an organism to produce a disease and survive.

Question 26

Give a few examples of virulence factors

Answer 26

1) polysaccharide capsule on bacteria allows them to adhere to other cells , or can also act to prevent phagocytosis and protect bacteria from antibodies. This increases likelihood of host entry
2) pili on the surface of bacteria allows adherence of bacteria to host cells or to other bacteria molecules to transfer their DNA
3) bacterial collagenase : which is used to break peptide bonds in collagen which is involved in the degradation of extracellular matrixes of animal cells. This increases invasiveness of bacteria.

Question 27

Give a few examples of toxins

Answer 27

1) exotoxins

2) endotoxins ( lipopolysaccharide)

Question 28

Outline the process of gram staining

Answer 28

1) application of crystal violet (purple dye) which binds to the peptidoglycan of bacteria ( this is thickest in gram positive bacteria)
2) You then apply iodine ( mordant)
3) you then alcohol wash which causes decolorisation
4) You then apply safranin which is a counterstain ( pinky)

Question 29

What colour would gram positive appear ?

Answer 29

Purple

Question 30

What colour would grade negative bacteria appear ?

Answer 30

Pink

Question 31

What does the term ‘cocci’ mean ?

Answer 31

Any bacterium or archaeology that has a spherical , ovoid or generally round shape

Question 32

What does the term ‘ bacillus’ mean ?

Answer 32

Rod shaped bacteria

Question 33

What does the term spirochetes mean?

Answer 33

Spiral shaped cells