Bugs In The System

Question 1

How could you distinguish between Gram Positive and Gram Negative bacteria?

Answer 1

• +ve Crystal violet binds to -ve charged components
• Iodine added to form large Crystal violet complexes
• Acetone/methanol used to wash sample; if stain retained sample is Gram Positive
• If stain removed sample is Gram Negative and is stained using red dye

Question 2

Why do Gram Positive and Gram Negative bacteria stain differently?

Answer 2

Peptidoglycan wall in Gram +ve can retain the Crystal violet stain when washed with methanol/acetone but lipopolysaccharide wall in Gram -ve cannot so must be stained with a red dye

Question 3

Why can some bacteria not be stained using Gram stain?

Answer 3

• Too small (e.g. Chlamydia)

- No peptidoglycan in cell wall (Mycobacteria)

Question 4

List 2 diseases associated with Mycobacteria

Answer 4

• Tuberculosis

- Leprosy

Question 5

What method could be used to stain Mycobacteria?

Answer 5

Acid Fast stain

Question 6

Why might knowing the cell wall composition of bacteria be if clinical importance?

Answer 6

• Endotoxin effects

- Target for ANTIBIOTICS as human cells do not have cell walls

Question 7

Briefly explain how bacteria can form a colony

Answer 7

• Single bacterium on an agar plate can multiply asexually by BINARY FISSION
• Growth is exponential so can have millions of bacteria after a short time

Question 8

List 3 ways in which bacteria can grow

Answer 8

• Broth (Planktonic)
• Colony
• Biofilms

Question 9

Give 2 examples of Gram Positive cocci and their associated diseases

Answer 9

• Staphylococci (cause skin lesions such as boils and cellulitis)
• Streptococci (cause pneumonia, scarlet fever)

Question 10

Give 2 examples of diseases that are associated with Neisserie (Gram -ve)

Answer 10

• Meningitis

- Gonorrhoea

Question 11

Define ‘infection’

Answer 11

The establishment of an organism on or in a host associated with its multiplication and damage to/dysfunction of the host, specifically related to that organism or its products

Question 12

What is unusual about mitochondrial lineage?

Answer 12

Maternal lineage only

Question 13

What 2 structures can bacteria exist in?

Answer 13

• COCCI (Staphylococci, Streptococci, diplococci)

- BACILLI (Clostridium)

Question 14

Give an example of a Gram Negative cocci

Answer 14

Neisseria

Question 15

Give an example of a Gram Positive bacilli and its associated diseases

Answer 15

• Clostridium
• Food poisoning (by Clostridium perfringens)
• Colitis (by Clostridium difficle)

Question 16

Give 3 examples of Gram Negative bacilli and an associated diseases for each

Answer 16

• SHIGELLA (diarrhoea)
• HELICOBACTER (duodenal and gastric ulcers)
• SALMONELLA (food poisoning)

Question 17

What bacteria is responsible for Cholera and what is the nature of this bacterium?

Answer 17

• Vibrio

- Gram -ve, comma shaped

Question 18

What is the clinical importance of bacterial growth?

Answer 18

• Can calculate the rate of reproduction

- Time to diagnose/take action

Question 19

What are the specific requirements for bacterial growth?

Answer 19

• Energy source
• Building blocks
• Atmosphere (habitat/reservoir)

Question 20

What is the difference between Gram Positive bacteria and Gram Negative bacteria?

Answer 20

Gram Positive bacteria have a peptidoglycan wall whereas Gram Negative bacteria have a lipopolysaccharide wall

Question 21

Give an example of a Gram Positive bacilli

Answer 21

Clostridium

Question 22

What is the name of the red dye used to stain Gram Negative bacteria?

Answer 22

Safranin