Bacteria As Pathogens Topic 6

Question 1

Structural differences between gram pos and gram neg bacteria

Answer 1

Gram neg- single thin layer of peptidoglycan with an outer membrane
Gram pos- thick multi layers of peptidoglycan and no outer membrane

Question 2

How do bacteria cause disease: endotoxins

Answer 2

Normally gram neg
Released when bacteria die and cell wall breaks down
Lipid part of the lipopolysaccharide outer membrane is the toxin

Question 3

Examples of endotoxin bacteria

Answer 3

Salmonella and E.coli

Question 4

Endotoxins and anti biotics

Answer 4

Some anti biotic treatments release endotoxins to destroy bacteria by lysis of cell wall

Question 5

How do bacteria cause disease: exotoxins

Answer 5

Mostly gram pos

Soluble proteins produced inside pathogenic bacteria as they grow and metabolise- released into body following lysis

Question 6

Where do exotoxins act?

Answer 6

Widespread- can act from a distance of infecting bacteria

Question 7

Examples of exotoxins bacteria

Answer 7

Staphylococcus

Question 8

How do bacteria cause disease: host tissue invasion

Answer 8

Pathogen invades tissue and damages cells
Symptoms of disease are caused by response of host to cell damage
Cell damage is often linked to exotoxin production or endotoxin presence in bacterial cell walls

Question 9

Bacteriostatic anti biotics

Answer 9

Stops growth of bacteria by interfering with their metabolic processes- DNA replication, protein synthesis

Question 10

Bactericidal anti biotics

Answer 10

Destroys bacteria by preventing formation of the cell wall

Question 11

What is penicillin?

Answer 11

Bactericidal- cell wall agents

Question 12

Broad spectrum anti biotic

Answer 12

Affects many different types of bacteria

Question 13

Narrow spectrum anti biotics

Answer 13

Affects specific bacteria. Better to use because it does not effect helpful bacteria and is likely to work more effectively

Question 14

What does the effectiveness of anti biotic treatment depend on?

Answer 14

How easily the drug can reach affected area
Local pH
If anti biotic is destroyed by host bacteria
How susceptible the bacteria is to the anti biotic

Question 15

Why is it difficult to treat gram negative bacteria?

Answer 15

Cell wall increases risk of toxicity
Channels are present in gram negative which prevent entry of anti biotics
Risk of resistance is greater due to outer membrane
Gram neg can have both exotoxins and endotoxins

Question 16

What is biological conjugation?

Answer 16

Transferral of anti biotic resistant gene among bacteria through pili using plasmid

Question 17

What are healthcare associated infections and give 2 examples

Answer 17

Infections patients get while receiving treatment for medical conditions
MRSA
Clostridium difficile

Question 18

Prevention and control of infection

Answer 18

• limit AB use
• finish AB course
• hygiene measures
• isolation of patients
• screening
• monitoring levels of HAI

Question 19

What is a pour plate culture

Answer 19

Inoculate plate with bacterium dilution
Spread evenly over sterile agar surface
Tape on lid and leave colonies to grow

Question 20

Streak plate culture

Answer 20

Using an inoculating loop streak bacterium over surface of 1/4
Sterilise look and streak next quarter dragging original bacterium from streak 1
Continue for 4 times
This will dilute bacteria further for every quarter allowing colonies to be seen

Question 21

What is a selective media?

Answer 21

Growth medium containing a very specific mixture of nutrients so only a particular microorganism will grow

Question 22

What is a differential media?

Answer 22

Biochemically distinguish between related groups of microorganisms- they will use the nutrients differently creating specific coloured colonies

Question 23

What does nutrient broth contain?

Answer 23

Protein source from blood, meat or yeast and sugars as respiratory substrate

Question 24

What is the aim of aseptic technique?

Answer 24

Only inoculate bacterium you desire

Avoid contaminating yourself and environment

Question 25

Name 3 ways of counting bacteria

Answer 25

1. Haemocytometer
2. Dilution plating
3. Optical method (turbidity)

Question 26

How do you measure fungus growth?

Answer 26

Measure area pi r 2 at the start of growth then again at end of growth
Calculate percentage change

Question 27

What are the density dependent limiting factors of bacterial growth?

Answer 27

Nutrients
Oxygen
Assimilation is toxic waste
Space

Question 28

Name the 4 phases of the growth curve

Answer 28

Lag phase
Log/ exponential growth
Stationary phase
Death phase

Question 29

Lag phase

Answer 29

Adaption to environment. Slow growth rate as bacteria are producing carrier proteins absorbing nutrients and producing enzymes to digest nutrients

Question 30

Log/ exponential growth phase

Answer 30

Binary fission begins. exponential growth occurs, unrestricted growth. cell division rate is higher than cell death rate

Question 31

Stationary phase

Answer 31

Limiting factors begin to impact. Cell division rate equals cell death right. It has reached its carrying capacity.

Question 32

Death phase

Answer 32

Death rate is greater than division rate so the population declines. Decline maybe slowed by the breakdown of dead cells releasing nutrients.

Question 33

Generation time

Answer 33

The time it takes for cell count to double each generation

Question 34

Exponential growth rate constant

Answer 34

The number of times the population will double in one unit of time

Question 35

When are metabolites produced?

Answer 35

Produced by an organism in its metabolic processes

Question 36

Primary metabolites

Answer 36

Essential proteins and enzymes for growth. Unhelpful for human use.

Question 37

Secondary metabolites

Answer 37

Begins to be produced in the log phase. Requires established population. Antibiotic chemicals or substrates can be derived which are helpful for human use