1.2 - Introduction To Microbes

Question 1

What are the 4 main types on microbes

Answer 1

Viruses
Bacteria
Fungi
Parasites

Question 2

Describe the structure of a virus

Answer 2

Circular, non membrane bound nucleic acid (DNA or RNA)

Protein Coat (provides resilience)

External Envelope (phospholipid bilayer)

Spikes ( proteins for attaching to specific cell surface)

Question 3

How is the the genetic code of viruses stored?

Answer 3

DNA viruses

• Single stranded non-enveloped (parvovirus 19)
• Double stranded non-enveloped (Adenovirus)
• Double stranded enveloped ( Hepatitis B)

RNA viruses
- Single stranded, positive strand, icosahedral, non-enveloped ( Hepatitis A and E)
- Single stranded positive strand icosahedral or helical, enveloped
(HIV, Hepatitis C, rubella)
- Single stranded, negative strand, helical, enveloped
(Ebola, Mumps, measles)
- Double stranded icosahedral, non enveloped.
(Rotavirus)

Question 4

What are bacteriophages

Answer 4

Viruses that infect bacteria.

Can be used to treat bacterial infections.

Question 5

Describe the bacterial cell structure

Answer 5

Large circular wrapped DNA
Plasmids (small amounts of free DNA, cause antibody resistance as can transfer between different bacteria of the same and different species)
Plasma membrane
Cell wall
Capsule
Flagellum 
Pili

Question 6

What are the three most common bacterial shapes?

Answer 6

Coccus
Spirillus
Bacillus

Question 7

How can cocci bacterium be arranged?

Answer 7

In clusters (staphylococcus)

In chains (streptococcus)

Question 8

What is the structural difference between gram positive and gram negative bacterium?

Answer 8

Gram positive = outer membrane consists of a plasma membrane, periplasmic space and a peptidoglycan coat

Gram negative = outer membrane consists of a plasma membrane, periplasmic space and a peptidoglycan coat and a LIPOPOLYSACCHARIDE layer

Question 9

What are aerobes?

Answer 9

Bacteria that can survive in the presence of oxygen

Question 10

What are obligate aerobes?

Answer 10

Bacteria that require oxygen for survival

Question 11

What are anaerobes?

Answer 11

Bacteria that can survive in the absence of oxygen

Question 12

What are obligate anaerobes?

Answer 12

Require an oxygen free environment for survival

Question 13

What are important gram positive coccus bacterium?

Answer 13

Staphylococcus aureus
Coagulase negative staphylococcus 
Streptococcus pyogenes
Streptococcus pneumonia
Enterococcus faecalis

Question 14

What are important gram negative coccus bacterium?

Answer 14

Neisseria meningitidis

Neisseria gonorrhoeae

Question 15

Name important gram positive bacillus bacterium

Answer 15

Listeria monocytogenes

Question 16

Name important gram negative bacillus bacterium

Answer 16

Escherichia coli
Salmonella typhi
Haemophilia influenza
Pseudomonas aeruginosa

Question 17

What are mechanisms of bacterial pathogenesis?

Answer 17

Virulence factors
– Host entry (e.g. polysaccharide capsule
– Adherence to host cells (e.g. pili and fimbriae)
– Invasiveness (e.g. enzymes such as collagenase)
– Iron sequestration (siderophores) •

Toxins
– Exotoxins (e.g.diphtheria toxin)
– Endotoxins (lipopolysaccharide)

Question 18

How do eukaryote ribosomes vary from prokaryote ribosomes?

Answer 18

Prokaryotes have 70S ribosomes

Eukaryotes have 80S ribosomes and 70S ribosomes in organelles

Question 19

What are yeasts?

Answer 19

A type of single celled fungi

Question 20

Give some names of yeasts

Answer 20

Candida albicans

Cryptococcus neoformans

Question 21

What are moulds?

Answer 21

A form of multicellular fungi

Question 22

Give an example of a pathological mould

Answer 22

Aspergillus species

Dermatophytes

Question 23

What are helminths?

Answer 23

Multicellular parasites. Worms. Examples are roundworms, tapeworms, flukes.

Question 24

whats the difference between DNA virus and a RNA virus?

Answer 24

DNA viruses such as adenoviruses and poxviruses are more likely to be double-stranded whereas most RNA viruses are single-stranded.
DNA viruses like the poxvirus are packaged with their polymerase machinery so they can replicate in the host cytoplasm directly. RNA viruses infect cells by injecting RNA into the cytoplasm of the host cells to transcribe and replicate viral proteins. RNA viruses also include retroviruses which use reverse transcriptase to create DNA from RNA templates.

Question 25

how are microorganisms named?

Answer 25

Linnean taxonomy

Question 26

what are collagenases?

Answer 26

Collagenases are enzymes that break the peptide bonds in collagen. They assist in destroying extracellular structures in the pathogenesis of bacteria such as Clostridium.

Question 27

what are the differences between protozoa and helminths?

Answer 27

both are parasites | protozoa are single celled and helminths are multi-cellular

Question 28

give some examples of protozoa that are parasites

Answer 28

giardia lamblia cryptosporidium parvum plasmodium falciparum (malaria)

Question 29

what is agar?

Answer 29

a polysaccharide derived from seaweed

Question 30

what properties of agar make it suitable for its use in the culturing of bacterium?

Answer 30

clearer than gelatin resists digestion by bacterial enzymes can be inoculated at 40oC in its cooled molten state and incubated at 60oC without melting can contain additional ingredients to help with bacterium growth

Question 31

why is the standard agar plate red?

Answer 31

due to the addition of blood

Question 32

what is chocolate agar?

Answer 32

Agara which contains lysed RBCs to release intracellular nutrients. Needed for the culture of haemophilus influenzae

Question 33

what is the main difference between prokaryotes and eukaryotes?

Answer 33

Cells that have a well-defined nucleus are called eukaryotic, whereas cells that lack a nucleus are called prokaryotic. All bacteria are prokaryotes

Question 34

what different layers can be contained within the cell envelope?

Answer 34

the cell wall cytoplasmic membrane envelope

Question 35

what is the cytoplasmic membrane?

Answer 35

also known as the cell membrane, it is composed of phospholipids and acts as a permeability barrier.

Question 36

the peptidoglycan layer is present in all bacterial cell walls. what is its function?

Answer 36

The peptidoglycan layer determines the shape of the cell. It is composed of a cross-linked polymeric mesh. The molecular structure of this layer helps render the bacterial wall resistant to host peptidases such as those in the intestine. This helps the bacteria survive in a hostile environment.

Question 37

why are gram negative bacterium more susceptible to physical damage than gram positive bacterium?

Answer 37

gram positive have a thick peptidoglycan cell wall. | gram negative cells have a thin peptidoglycan and therefore are more susceptible to physical damage.

Question 38

what can be used to identify different strains of gram negative bacterium?

Answer 38

the polysaccharide portion of the outer lipopolysaccharide layer is antigenic and can therefore be used to identify different strains of the bacterium

Question 39

what is the bacterial capsule?

Answer 39

the bacterial capsule is a sticky, viscous material that forms an extracellular coating around the cell. The material is usually a polysaccharide.

Question 40

what is the function of the bacterial capsule?

Answer 40

- allows cells to adhere to surfaces - protect bacteria from antibodies and phagocytosis - act as diffusion barriers against some antibiotics thus contributing to the organisms’ pathogenicity - protect bacteria against desiccation, or drying, which facilitates transmission.

Question 41

what bacteria have a capsule?

Answer 41

streptococcus pneumoniae neisseria meningitidis Group B streptococcus haemophilus influenzae type b

Question 42

what patients are at increased risk of an infection from encapsulated bacterium?

Answer 42

those that have undergone a splenectomy or have a defective spleen. The spleen has an important role in recognising and removing encapsulated bacterium

Question 43

what is a gram stain?

Answer 43

colouring of patient material prior to examination under a light microscope. Helps to distinguish between gram positive and gram negative bacterium

Question 44

what are the main principles of performing a gram stain?

Answer 44

treat with crystal violet treat with iodine gram positive purple microorganisms identified treat with solvent (alcohol/acetone) gram positive bacterium retain the stain, gram negative so not as the alcohol removes the external lipopolysaccharide safranin stains the gram-ve bacterium pink