Staph

Question 1

what shape is Staphylococcus?

Answer 1

cocci, like a bunch of grapes

Question 2

what oxygen levels does Staph require?

Answer 2

facultative anaerobe

Question 3

how does Staph metabolise?

Answer 3

fermentation AND respiration

Question 4

what does Staph produce as a result of metabolism?

Answer 4

lactic acid

Question 5

how to distinguish Staph from Strep?

Answer 5

Staph= catalase POSITIVE

Question 6

what is the GC content of Staph?

Answer 6

30-40 (low)

Question 7

is S.aureus coagulase positive/negative? what is this used to distinguish from?

Answer 7

POSITIVE- used to distinguish from S.epidermidis and micrococcus
plasma clots by conversion of fibrinogen to fibrin

Question 8

where is S.aureus normally found?

Answer 8

skin, nose

Question 9

who does pneumonia and septicaemia caused by S.aureus affect most?

Answer 9

newborns and immunocompromised (eg burns)

Question 10

how does S.aureus cause skin infections?

what does it cause?

Answer 10

invades subcutaneous tissue using LIPASES, causes inflammation, forms FIBRIN SACK, attract neutrophils to site, release LEUKOCIDIN that KILLS neutrophils—> PUS formed
causes furuncles, carbuncles and impetigo

Question 11

what is septic arthiritis? what is it caused by ?

who does it affect?

Answer 11

caused by S.aureus, Strep.pyogenes

• infection of JOINT (via trauma/blood infection/surgery)
• babies, young children

Question 12

what is osteomyelitis? what is it caused by ?

who does it affect?

Answer 12

caused by S.aureus
- infection of BONE
- direct INOCULATION OR
if bacteria are SEEDED FROM BLOOD- HEMATOGENOUS osteomyelitis
- commonly in children (fast growth of bone, blood can DEPOSIT bacteria)

Question 13

what is responsible for Scalded Skin Syndrome? symptoms?

Answer 13

caused by S.aureus that is CARRYING A BACTERIOPHAGE which expresses exfoliatin toxin (A or B).

• symptoms remote from actual site of infection
• desquamation (skin peeling)

Question 14

what causes Endocarditis? what does it affect?

Answer 14

S.aureus

affects heart tissue, valves.

Question 15

roughly what % of us carry S.aureus? what about in hospitals?

Answer 15

25%

but higher in hospital 50-70% in hospital staff

Question 16

what can be a cause of wound infections and absesses?

Answer 16

S.aureus

- commonly hospital acquired (nosocomial)

Question 17

how are HEMOLYSINS used as a virulence factor?

Answer 17

TOXIN - can lyse erythrocytes & other cell types

Question 18

how are LEUKOCIDINS used as a virulence factor?

Answer 18

TOXIN - acts on polymorphonuclear leukocytes & macrophages

Question 19

how are EXFOLIATINS used as a virulence factor?

Answer 19

PLASMID- encodes skin toxin, causing peeling of epidermis

Question 20

how are ENTEROTOXINS A, B & D used as virulence factors?

Answer 20

EXOTOXINS- cause food poisoning, severe vomiting and diarrhoea
- are heat stable- resist boiling

Question 21

how is TSST-1 used as a virulence factor?

Answer 21

SUPERANTIGEN- stimulates T cells in a NON ANTIGEN SPECIFIC WAY to activate MACROPHAGES to release TNF/cytokines—> shock

Question 22

how are LIPASES used as virulence factors?

Answer 22

LIPID HYDROLYSIING ENZYME- allows organisms to invade tissues

Question 23

how are FIBROLYSINS used as virulence factors?

Answer 23

dissolves fibrin clots, causes SPREAD

Question 24

how is EXTRACELLULAR COAGULASE used as a virulence factor?

Answer 24

involved in forming FIBRIN wall of absesses

Question 25

what produces Panton Valentine Leukocidin?
where is it found to cause disease?
who does it affect?

Answer 25

bacteriophage carrying lukF and lukS genes produce Panton Valentine Leukocidin

• V INVASIVE soft tissue inf
• community acquired (sometimes hospital outbreaks)
• young and healthy

Question 26

what is the mechanism of Panton Valentine Leukocidin?

Answer 26

acts w/ other leukocidins to LYSE HOST CELL MEMBRANES

causes invasive soft tissue inf

Question 27

what is S.aureus naturally resistant to? why?

how do we target this?

Answer 27

resistant to PENICILLIN, as it prod penicillinase (naturally)
target: make synthetic penicillins: oxacillin, METHICILLIN

Question 28

some strains of S.aureus are resistant to what?

what is the concern about this?

Answer 28

METHICILLIN (MRSA)

O cannot use Methicillin to treat

Question 29

what is used to treat MRSA?

Answer 29

VANCOMYCIN- (also targets peptidoglycan synth)

Question 30

what has been found to be resistant to Vancomycin?

how did this happen?

Answer 30

Enterococcus faecalis

- DNA cont Vacomycin resistance passed from Enterococcus into MRSA via CONJUGATION of plasmid

Question 31

where is MRSA commonly found?

Answer 31

in HOSPITAL healthcare setting USUALLY

Question 32

where is MRSA less commonly found? who does it affect?

Answer 32

community- (C-MRSA)
affects: immunocompetent but
INJECTING DRUG USER, MASSAGE PARLOURS, RUGBY, WRESTLING (close contact)

Question 33

describe Staph. epidermidis

Answer 33

• non haemolytic

- coagulase -VE

Question 34

where is Staph. epidermidis found?

Answer 34

very common on skin flora, gut and resp tract

Question 35

how common are S.epidermidis infections?

Answer 35

less common than S.aureus

Question 36

where are the major infections of Staph. epidermidis found in the body?
what type of infection?

Answer 36

catheters, shunts and prosthetic heart valves

NOSOCOMIAL

Question 37

does Staph have low or high GC content?

Answer 37

low (firmicute)

Question 38

is Staph a lactic acid bacteria?

Answer 38

yes