Staphylococci

Question 1

are staphs gram positive or negative?

Answer 1

positive

Question 2

what class of ‘respiration?’ are staphs?

Answer 2

facultative anaerobes

Question 3

are staphs coagulase negative or positive?

Answer 3

both

Question 4

is staph aureus coagulase positive or negative?

Answer 4

positive

Question 5

is staph epidermidis coagulase positive or negative?

Answer 5

negative

Question 6

how would you describe an irregular cluster of staph?

Answer 6

bunches of grapes

Question 7

coagulase test - what does it mean?

Answer 7

does the organism PRODUCE coagulase

Question 8

which media is selective for staphs?

Answer 8

mannitol salt

Question 9

why is mannitol salt selective for staphs?

Answer 9

high salt concentration and contains mannitol

Question 10

what does it mean if mannitol salt turns yellow?

Answer 10

the organism ferments mannitol and produces acid which turns the agar yellow

Question 11

is staph aureus catalase positive or negative?

Answer 11

positive

Question 12

is staph epidermidis catalase positive or negative?

Answer 12

positive

Question 13

how can you identify different types of strains of staphs?

Answer 13

• phage typing
• antibiotic resistance profiles
• DNA sequencing
• plasmid profiling
• RFLPs

Question 14

what are phages?

Answer 14

viruses that affect bacteria

Question 15

what is RFLPs and what do you do?

Answer 15

chop chromosome up, run gel, see fragments, bacterial fragments

Question 16

how do staphs spread?

Answer 16

lymphatic/blood stream

Question 17

what virulence factor does staph aureus have?

Answer 17

hyaluronidase - breaks down hyaluronic acid - breaks down skin

Question 18

what other enzymes do staphs have?

Answer 18

collagenases

elastases

lipases

haemolysins

Question 19

what factors make you susceptible to staph infections?

Answer 19

• excessive moisture e.g. armpits, groin
• trauma - broken skin
• catheters
• compromised blood supply - aerobic but can grow anaerobic
• person-person transmission

Question 20

what are the most common staph hospital infections?

Answer 20

MSSA/MRSA

Question 21

what does staph aureus look like on blood agar?

Answer 21

haemolytic

Question 22

what is the difference between MSSA and MRSA

Answer 22

MSSA = normal staph aureus
MRSA = resistant strain

Question 23

what sort of diseases are associated with staph aureus?

Answer 23

• septicaemia
• endocarditis
• osteomyelitis
• Toxic shock syndrome
• pneumonia

Question 24

what other conditions are associated with staph aureus?

Answer 24

• Boils
• skin abscesses
• post-op wound infection
• scalded skin syndrome
• catheter-associated infection
• foodborne infection

Question 25

what other virulence factors do staphs have?

Answer 25

capsule
protein A
range of toxins
slime layer

Question 26

what does coagulase virulence factor do?

Answer 26

converts fibrinogen to fibrin

accumulates around cells and protects cell from the host immune system

Question 27

what is protein A and what does it do?

Answer 27

surrounds the organism and binds to immunoglobins - Fc end of IgG, inhibiting the complement cascade to prevent phagocytosis

Question 28

what toxins can staphs produce? and what do they do?

Answer 28

haemolysin and leukocidin - against red/white blood cells - burst membranes

hyaluronidase - hydrolyse connective tissue

Question 29

what are enterotoxins and what do they do?

Answer 29

food poisoning - act on the vomiting centre

Question 30

what are boils and what do they do?

Answer 30

the initial lesion is often mild and around hair follicles

it provokes an intense inflammatory response but is sealed off by fibrin and protected from host defences - more and more blood is sent to the area - causes swelling

Question 31

why should you burst a boil?

Answer 31

release pus - otherwise will infect the blood and cause septicaemia

Question 32

what causes pus?

Answer 32

leukocidin and enzymes

Question 33

why are boils painful?

Answer 33

swelling on the nerves

Question 34

what is pus made up of?

Answer 34

white cells and dead bacteria

Question 35

what causes impetigo?

Answer 35

staph aureus

Question 36

what is impetigo?

Answer 36

a non-invasive local skin infection - very infectious

Question 37

how is impetigo spread?

Answer 37

through minor lesions

Question 38

what toxin causes scalded skin syndrome and what does it do?

Answer 38

exfolatin toxin - takes off superficial epidermal layers

toxins carried by circulatory system

Question 39

what are the symptoms of TSS?

Answer 39

fever, skin rash, hypotension, skin loss from TSS toxin

Question 40

what is osteomyelitis?

Answer 40

Inflammation of the bone and surrounding tissues

Question 41

if a patient is infected by staph epidermidis via a catheter, what can it cause?

Answer 41

septicaemia

Question 42

what happens if staph epidermidis infects a burn?

Answer 42

necrotic tissue and WBC suppression

Question 43

what happens if staph epidermidis infects prostetics?

Answer 43

causes endocarditis in prosthetic valves

Question 44

what virulence factors does staph epidermidis have to infect prosthetics?

Answer 44

slime layer to stick to plastics

Question 45

what virulence factors does staph epidermidis have against white blood cells?

Answer 45

biofilm to stick to wbc

Question 46

what is endocarditis?

Answer 46

localised infection of cardiac valves

Question 47

what are the symptoms of acute endocarditis?

Answer 47

high fever

Question 48

what are the symptoms of subacute endocarditis?

Answer 48

low fever
weakness
weight loss
abnormal valves

Question 49

what factors increase susceptibility to endocarditis?

Answer 49

congenital heart disease
valve disease
prosthetic valve

Question 50

60% of what organism causes endocarditis?

Answer 50

s. aureus