Session 6 Lecture Notes

Question 1

What is a surface (for infection spread?)

Answer 1

An interface between a solid and either a liquid or gas

Question 2

What are the 2 surface types on a patient?

Answer 2

1. Skin

2. Mucosal surfaces

Question 3

Give some examples of mucosal surfaces in our body

Answer 3

1. Conjunctival (eye)
2. GI
3. Respiratory
4. Genitourinary

Question 4

What are the viruses that can be found on the skin?

Answer 4

Papilloma

Herpes simplex

Question 5

What gram positive bacteria are found on the skin? List 3 of the most common types

Answer 5

1. Staph aureus
2. Coagulate negative staphylcocci
3. Cornyebacterium

Question 6

Name a gram negative bacteria found on the skin

Answer 6

Enterobacteriaceae

Question 7

What gram positive bacteria is often found in contaminated blood samples?

Answer 7

Coagulase negative staphylococci

Question 8

What causes tonsillitis?

Answer 8

Invasion of strep pyrogenes pharyngitis into the tonsils

Question 9

What gram positive bacteria commonly causes infections around artificial joint surfaces?

Answer 9

Coagulase negative staphylococcus

Question 10

What is a haematogenous spread of infection?

Answer 10

Blood borne spread of infection

Question 11

What gram positive bacteria commonly cause endocarditis?

Answer 11

Coagulase negative staphylococcus

Question 12

Give some examples of prosthetic surface infection locations

Answer 12

1. Peritoneal dialysis catheter
2. IV lines
3. Prosthetic joints
4. Cardiac valves

Question 13

When might viridans streptococci cause endocarditis ?

Answer 13

1. In a native heart valve

2. In a valve replacement that is less than a year old

Question 14

When does coagulase negative staphylococci cause endocarditis?

Answer 14

In a heart valve replacement that is over a year old

Question 15

What 2 bacteria commonly cause infections at prosthetic joint surfaces?

Answer 15

1. Coagulase negative staphylococcus

2. Staph aureus

Question 16

What structures of the bacteria help them to attach and create a biofilm?

Answer 16

Pilli

Question 17

What are the 3 principles of biofilm formation?

Answer 17

1. Autoinducers are secreted
2. These bind to receptors on nearby bacteria
3. This activates the receptor and causes more release of autoinducers and co-ordinates activity

Question 18

Streptococci is a gram positive or negative bacteria?

Answer 18

Gram positive cocci

Question 19

Streptococci can be classified by haemolysis

What are the 3 categories and how do they affect the RBCs on the blood afar plate?

Answer 19

1. Gamma (non-haemolytic) - ie no destruction of RBCs
2. Alpha haemolysis - partial break down of RBCs
3. Beta haemolysis - complete break down of RBCs

Question 20

What is the class of streptococci that produce alpha haemolysis?

Answer 20

Viridans streptococci

Question 21

Why do viridans streptococci have a wet appearance on a blood agar plate?

Answer 21

They have a carbohydrate capsule which makes the organism more virulent

Question 22

What could you expect to see on a blood agar plate of a streptococci that is beta haemolytic?

Answer 22

Clear zones where all that is left is the agar (jelly) - as the RBCs have been completed destroyed

Question 23

What does the Lancefield classification of streptococci do?

Answer 23

Separate BETA-haemolytic streptococci (fully haemolytic) into groups based upon their cell wall antigens

Question 24

What does the Sherman classification of streptococci do?

Answer 24

Separate Streptococci into 4 different classes

1. Pyogenic (pus forming)
2. Viridens
3. Enterococcal
4. Lactic

Question 25

What Lancefield group is Streptococcus Pyogenes?

Answer 25

Group A beta-haemolytic streptococci (completely breaks down RBCs)

Question 26

Streptococcus pyogenes has a number of virulence factors | Name as many as possible

Answer 26

``` Hyaluronic acid capsule M Protein Adhesins Streptolysins O and S Dnases A-D Hyaluronidase and Streptokinase Streptococcal pyrogenes exotins ```

Question 27

What does a hyaluronic acid capsule do? (virulence factor of streptococcus pyogenes)

Answer 27

Inhibits phagocytosis

Question 28

What does the M protein do? (virulence factor of streptococcus pyogenes)

Answer 28

Prevents phagocytosis by inhibiting activation of alternative complement pathway on bacterial cell surface

Question 29

What do adhesins do? (virulence factor of streptococcus pyogenes) Give a couple of examples

Answer 29

Help the bacteria adhere to epithelial surfaces (first step in colonisation/infection) M proteins and fibronectin binding protein act as adhesins

Question 30

What do Streptolysins O and S do? (virulence factor of streptococcus pyogenes)

Answer 30

Lysis of RBCs neutrophils and platelets (cause of haemolysis)

Question 31

What do Dnases A, B, C and D do?

Answer 31

When neutrophils approach a bacteria to neutralise it, they condense their DNA (as they are about to self-destruct) and they expel this as a net to help catch the pathogen Dnases break down DNA so inactivate this method in neutrophils

Question 32

What do streptococcal pyrogenic exotoxins do?

Answer 32

They cleave IgG bound to Group A Strep (breaking down the antibody response in the host cell)

Question 33

What bacteria is the common cause of streptococcal pharyngitis?

Answer 33

Streptococcus pyogenes (Group A beta haemolytic streptococci - which is a gram positive bacteria)

Question 34

What happens if you don't treat a patient with streptococcal pharyngitis?

Answer 34

The patient will develop an M protein specific antibody but there are some occasional complications such as scarlet fever

Question 35

Name 4 complications from streptococcal pharyngitis

Answer 35

1. Scarlet fever 2. Suppurative complications (pus forming) 3. Acute rheumatic fever 4. Acute post-streptococcal glomerulonephritis

Question 36

What skin infections can streptococcus pyogenes cause?

Answer 36

1. Impetigo 2. Erysipelas 3. Cellulitis 4. Necrotising fasciitis

Question 37

What bacteria/s causes impetigo? | What can impetigo lead to?

Answer 37

Streptococcus pyogenes or staph aureus | It can lead to glomeuruonephritis

Question 38

What are the 4 signs of toxic shock syndrome?

Answer 38

1. Deep tissue infection with streptococcus pyogenes 2. Bacteraemia (bacteria in the blood) 3. Vascular collapse 4. Organ failure