Gram Positive Bacteria

Question 1

What makes a gram positive bacteria differnet from a gram negative?

Answer 1

A thick peptidoglycan layer
No outer Lipopolysaccharide layer.

Question 2

Why is gram staining useful?

Answer 2

• Some antibiotics are effective against gram +ve or gram -ve.
• gram staining gives us an early indication of the type of bacteria which may be causing infection

Question 3

What are the 3 types of gram +ve Cocci?

Answer 3

Staphylococci (clusters)
Streptococci (Chains)
Enterococci

Question 4

What are the subtypes of Staphylococci?

Answer 4

Coagulase postive & coagulase negative

Question 5

What is the main coagulase postive staphylococci?

Answer 5

Staphylocci Aureus
A commensal microbe in the nose, axilla & perineum.
Major pathogen

Question 6

Why is Staphylococci Aureus commonly resistant to penicillin?

Answer 6

Beta-lactamase causes penicillin resistance.

Question 7

Where are coagulase negative staphylococci?

Answer 7

Theyre commensals in the skin

Question 8

How do coagulase negative staphylococci become pathogenic?

Answer 8

In the prescence of foreign bodies or prostheses.

Question 9

What are the 2 subtypes of Streptococci?

Answer 9

Alpha- (partial haemolysis) & Beta-haemolytic (complete haemolysis).

Question 10

What culture is used to distinguish between alpha- & beta-haemolytic streptococci?

Answer 10

Blood Agar culture
alpha-haemolytic turns it green
beta-haemolytic turns it clear

Question 11

Name and detail an example of alpha-haemolytic streptococci?

Answer 11

Streptococci Pneumoniae
- normal mouth flora (commensal)
- Causes infective endocarditis

Question 12

How are beta-haemolytic streptococci further divided?

Answer 12

Into groups A-G.
A,B & D are clinically significant

Question 13

Name and detail a common Group A beta-haemolytic streptococci?

Answer 13

Streptococcus Pyogenes
A major pathogen causing sore throat & cellulitis.

Question 14

Name & detail a common group B beta-haemolytic streptococci?

Answer 14

Streptococcus Agalactiae
Causes neonatal sepsis with meningitis & bacteraemia.
Commonly carried in women’s genital tract.

Question 15

What is special about group D beta-haemolytic streptococcus?

Answer 15

Theyre actually non-haemolytic (SHOCKER).
known as enterococci.

Question 16

Name & detail a common enterococcus

Answer 16

Enterococcus Faecalis
A normal gut commensal that can cause UTI’s.

Question 17

Name the 3 common types of Anaerobic Gram-Positive Bacilli?

Answer 17

• Clostridium Difficile
• Clostridium Perfringens
• Clostridium Tetani

Question 18

Can Clostridium Difficile be cultured?

Answer 18

TEchnically yes but its very difficult

Question 19

What does clostridium difficile infection cause?

Answer 19

It produces toxins that cause diarrhoea & pseudomembranous colitis (inflammation of the wall of the colon)

Question 20

How does clostridium difficile spread?

Answer 20

Via spores, often in hospitals.

Question 21

What increases risk of pathogenic clostridium difficle infection?

Answer 21

Anything that disrupts normal gut flora, such as antibiotic use.

Question 22

How is a clostridium difficile infection detected?

Answer 22

Antigen & toxin can be detected in a stool sample

Question 23

Where is clostridium perfringens found?

Answer 23

In the gut as a normal commensal.
Also in food & wounds

Question 24

What does clostridium perfringens cause?

Answer 24

“Gas Gangrene” in wounds.
Food poisoning in food.

Question 25

What does clostridium tetani cause?

Answer 25

Tetanus by releasing toxins that inhibit nerve synapses from releasin inhibitory neurotransmitters (paralysis).

Question 26

How is clostridium tetani vaccinated against?

Answer 26

Using an antigenically modified toxin (toxoid)

Question 27

How are aerobic gram positive bacilli used in biological warfare?

Answer 27

Bacillus Anthracis (aerobic) is the cause of anthrax.

Question 28

What is the source of botox?

Answer 28

Clostridium Botulinum

Question 29

Classify Clostridium Botulinum:

Answer 29

Gram +VE
-> Anaerobic
-> Bacilli
-> Clostridium sp.
-> Clostridium Botulinum