Biology and classification of Bacteria

Question 1

What is a pathogen?

Answer 1

Organism that causes or is capable of causing disease

Question 2

What is a commensal?

Answer 2

Organism which colonises the host but causes no disease in normal circumstances

Question 3

What is an opportunist pathogen?

Answer 3

Microbe that only causes disease if host defences are compromised

Question 4

What is virulence/pathogenicity?

Answer 4

The degree to which a given organism is pathogenic

Question 5

What is asymptomatic carriage?

Answer 5

When a pathogen is carried harmlessly at a tissue site where it causes no disease

Question 6

How does a commensal become an opportunist pathogen?

Answer 6

Commensals can cause disease when they escape areas where they normally reside and become opportunist pathogen

Question 7

What colour stain do gram positive bacteria have?

Answer 7

Purple

Question 8

What colour stain do gram negative bacteria have?

Answer 8

Pink

Question 9

What does bacillus mean?

Answer 9

A rod

Question 10

What does spirochaete mean?

Answer 10

Spiral rod

Question 11

How many membranes do gram positive bacteria have?

Answer 11

1

Question 12

How many membranes do gram negative bacteria have?

Answer 12

2

Question 13

What is between the outer and inner membrane in gram negative bacteria?

Answer 13

lipoprotein, periplasmic space and peptidoglycan

Question 14

What is an endotoxin?

Answer 14

component of the outer membrane of bacteria, e.g. lipopolysaccharide in gram negative bacteria only

Question 15

What is an exotoxin?

Answer 15

secreted proteins of gram positive and gram negative bacteria
- can cause damage to host cell

Question 16

What pH do bacteria grow between?

Answer 16

4-9

Question 17

Which type of light can bacteria grow under?

Answer 17

UV
Can survive radiation

Question 18

How long do viruses take to double?

Answer 18

<1 hr

Question 19

How long does E.coli, S.aureus etc take to double?

Answer 19

20-30 mins

Question 20

How long does fungi take to double?

Answer 20

30 mins

Question 21

Are the actions of exotoxins specific or non-specific?

Answer 21

Specific

Question 22

Are the actions of endotoxins specific or non-specific?

Answer 22

Non-specific

Question 23

What is the composition of exotoxins?

Answer 23

Protein

Question 24

What is the composition of endotoxins?

Answer 24

lipopolysacccharide

Question 25

What effect does heat have on exotoxins?

Answer 25

Liable to change

Question 26

What effect does heat have on endotoxins?

Answer 26

Stable

Question 27

What are exotoxins produced by?

Answer 27

Gram positive and negative bacteria

Question 28

What are endotoxins produced by?

Answer 28

Gram negative bacteria

Question 29

Can exotoxins be converted to toxoids?

Answer 29

Yes

Question 30

Can endotoxins be converted to toxoids?

Answer 30

No

Question 31

What are some examples of mutation?

Answer 31

- Base substitution - Deletion - Insertion - Transfer

Question 32

What are 3 types of gene transfer?

Answer 32

- Transformation eg via plasmid - Transduction eg via phage - Conjugation eg via sex pilus

Question 33

What are obligate intracellular bacteria?

Answer 33

grow inside cells, can’t culture normally

Question 34

What is an example of obligate intracellular bacteria?

Answer 34

Chlamydia

Question 35

What are the 2 types of bacteria that may be cultured on artificial media?

Answer 35

With and without a cell wall

Question 36

What are the 2 types of bacteria with a cell wall?

Answer 36

1. Growing as single cells 2. Growing as filaments

Question 37

What are the 3 groups of bacteria that grow as single cells?

Answer 37

1. Rods 2. Cocci 3. Spirochaetes

Question 38

What are the 2 groups of cocci?

Answer 38

1. Gram negative 2. Gram positive

Question 39

What can gram negative and gram positive bacteria be further categorised into?

Answer 39

Aerobic and anaerobic

Question 40

What is N. meningitidis?

Answer 40

Aerobic gram negative cocci

Question 41

What are examples of aerobic gram negative cocci?

Answer 41

Neisseria 1. N. Meningitidis 2. N. Gonorrhoeae

Question 42

What are the 2 groups of aerobic gram positive cocci?

Answer 42

Staphylococcus Streptococcus

Question 43

What is the main cause of lobar pneumonia?

Answer 43

S. pneumoniae

Question 44

What is s. pneumoniae?

Answer 44

Alpha-haemolytic streptococcus

Question 45

What are the 3 groups of rod bacteria?

Answer 45

1. Gram positive 2. Gram negative 3. Ziehl-Neelsen stain positive

Question 46

What are an example of Ziehl-Neelsen stain positive bacteria?

Answer 46

Mycobacteria eg. M. tuberculosis

Question 47

What is the main cause of food poisoning in the UK?

Answer 47

Campylobacter

Question 48

Describe the gram staining process

Answer 48

1. Apply a primary stain such as crystal violet (purple) to heat fixed bacteria 2. Add iodide which binds to crystal violet and helps fix it to the cell wall 3. Decolourise with ethanol or acetone 4. Counterstain with safranin (pink)

Question 49

What is the coagulase test?

Answer 49

Distinguishes S.aureus from other staphylococci – coagulase positive

Question 50

What are the 3 types of haemolysis?

Answer 50

Alpha Beta Gamma

Question 51

What is alpha haemolysis?

Answer 51

haemolysis causing by production of hydrogen peroxide oxidising haemoglobin – the agar appears green

Question 52

What is beta haemolysis?

Answer 52

haemolysis results because of lysis of red blood cells by haemolysis such as Streptolysin O produced by S.pyogenes

Question 53

What is gamma haemolysis?

Answer 53

implies no haemolysis

Question 54

What is the oxidase test?

Answer 54

Tests if micro-organism contains a cytochrome oxidase – implies organism able to use oxygen as the terminal electron acceptor