Gram positive cocci: Staphylococci

Question 1

who first discovered Staphylococcus

Answer 1

Sir Alexander Ogston

Question 2

who Differentiated between S.aureus and S. epidermidis

Answer 2

Anton Friedrich Julius Rosenbach

Question 3

Nomenclature of staphylococcus

Answer 3

S.aureus was named after its golden colour.
S.epidermidis is named as it is found on the epidermis

Question 4

how is staphylococci classified

Answer 4

Gram positive cocci(spherical): 0.5-1.0 µm in diameter
Facultative anaerobes.
Grow in 18oC - 40oC
Catalase positive
Major differentiating feature is coagulase

Question 5

describe the classification of staphylococci

Answer 5

Kingdom: Bacteria, Family: Staphylococcoceae, Genus: Staphylococcus (Grape-like clusters), Species: 11 groups

Question 6

how to test if bac is Coagulase positive or negative?

Answer 6

Question 7

describe the Mechanisms of pathogenicity Staphylococcus aureus

Answer 7

Ability to COLONISE the host and invade tissues
Ability to EVADE host defences
Ability to damage host through production of invasins and exocellular toxins.
Ability to acquire RESISTANCE to antibiotics

Question 8

true or false is Staphylococcus aureus known as a true pathogen

Answer 8

true

Question 9

how is MRSA able to acquire RESISTANCE to antibiotics

Answer 9

Methicillin is a beta-lactam antibiotic used against beta-lactamase-producing staphylococci.
Only used for a year before MRSA was first described.
By 1970, it was recognised as a hospital pathogen.
Rapid spread through hospitals from 1980 to 2005.
50% of S.aureus are now MRSA

Question 10

what does MRSA stand for

Answer 10

Methicillin-resistant staphylococcus aureus.

Question 11

How does S.aureus become MRSA?

Answer 11

MecA (30-50kb) incorporated on SCCmec (staphylococcal cassette chromosome mec)

Encodes for additional penicillin binding protein (PBP2a); reduced affinity for beta-lactams

MRSA resistant to all beta-lactam antibiotics

Question 12

what treatment is used for MRSA infection

Answer 12

vancomycin

Question 13

How Vancomycin works

Answer 13

Interferes with cell wall synthesis by binding to D-ala-D-ala.
Blocks transglycosidase enzymes

Question 14

describe the characteristics of MRSA with reduced susceptibility to Vancomycin (VISA)

Answer 14

VISA has the MecA gene AND a thick cell wall.
Acts as a sponge, making it difficult for Vancomycin to penetrate the cell wall.

Question 15

what does VISA stand for

Answer 15

Vancomycin Intermediate Staphylococcus aureus (VISA)

Question 16

describe the characteristics of Vancomycin resistant staphylococcus aureus (VRSA)

Answer 16

VRSA contains MecA gene AND vanA gene.
vanA gene alters the D-ala-D-ala subunit to D-ala-D-lac

Question 17

what are the Clinical manifestations

Answer 17

Localised CVC catheter infection
Deep seated CVC catheter infection

Question 18

name the Clinically important Staphylococci

Answer 18

• Staphylococcus aureus (S.aureus)
• Staphylococcus epidermidis (S.epidermidis)
• Methicillin-resistant staphylococcus aureus (MRSA)

Question 19

name a specific clinical setting where S.aureus can be found

Answer 19

Over 60% of surgical infections are caused by S.aureus

Question 20

name a specific clinical setting where can S.epidermidis can be found

Answer 20

Over 60% of surgical infections are caused by S.aureus

Question 21

specific characteristic of mrsa

Answer 21

Causes same symptoms as S.aureus but more difficult to treat.

Question 22

Clinical significance of S.aureus and MRSA

Answer 22

S.aureus is a ‘true pathogen’ and can colonise anywhere on our skin.
S.aureus can colonise in the nose or on the skin of a healthy individual.
Particularly relevant to surgical site wounds.
Antibiotic resistant strains, like MRSA, make it difficult to treat the infection.

Question 23

describe what can be seen in a staphylococci infection of the skin

Answer 23

Impetigo Skin infection that starts with red blisters that burst to form yellow crusts.

Cellulitis Deep skin infection that causes the skin to be painful and hot

Skin abscesses A pocket of pus, deep within the skin.

Blepharitis Inflammation of the eyelids that causes scaly patches of skin near the eyelashes

Question 24

explain what Hospital infections are caused by Staphylococcus

Answer 24

Catheter-Related Urinary Tract Infection (CRUTI) Catheter introduces S.aureus or S.epidermidis directly to the bladder causing a UTI

Bacteraemia Bacteria in the blood. Can be fatal, as it triggers the bodies septic response

Endocarditis Inflammation of the inner values of the heart.

Question 25

explain how Staphylococcus aureus colonises the host

Answer 25

There are a group of proteins called Microbial Surface Components Recognising Adhesive Matrix Molecules (MSCRAMMS). Over 20 of these proteins have been discovered so far.
One of the MSCRAMMS is called Clumping factor (ClfA), which promotes adhesion to damaged tissue by binding to fibrinogen and expressing fibrin. It is sometimes also referred to as ‘bound coagulase’.
Another MSCRAMM is the Fibronectin binding protein (FnbpA), which binds to fibronectin. Fibronectin is present on the extracellular surface of healthy endothelial and epithelial surfaces.
Lastly, there are collagen (Cna) and elastin (EbpS) binding proteins, which help promote adhesion to severely damaged tissue.

Question 26

what is clumping factor A (ClfA)

Answer 26

Question 27

explain how Staphylococcus aureus evades the host

Answer 27

Question 28

explain neutrophil avoidance

Answer 28

Both bound coagulase and free coagulase when bound to fibrinogen in the plasma result in fibrin clots.

These clots allow for bacterial agglutination within the fibrin clots themselves.

This results in the neutrophils being unable to bind the bacterial cell surface.

As a result the phagocytosis is minimised.

Question 29

what is the function of Protein A

Answer 29

Question 30

explain how Staphylococcus aureus damages the host