Staphylococcus spp.

Question 1

Gram Positive Cocci

Answer 1

Staph
Strep

Question 2

GPC Grape-like cluster

Answer 2

Staph

Question 3

Staph culture conditions

Answer 3

Aerobic 37C Blood Agar

Question 4

Staph colony morphology

Answer 4

2-3mm round raised white/cream

Question 5

Colony morphology:
Blood Agar
2-3mm, round, raised, white/cream.
No haem

Answer 5

?Staph

Question 6

Presumptive Staph tests

Answer 6

1. Tube coagulase test
2. Staphaurex Plus test
3. DNase test
4. S/D - Mannitol Salt agar/ CHROMID agar test.

Question 7

Staph Aureus infections

Answer 7

Superative infections:
1. Infection of hair follicles - folliculitis, furuncles, carbuncles.
2. Impetigo (pustular, bullous)
3. Cellulitis
4. Mastitis
5. Surgical wounds
6. Abscesses
Systemic infections:
1. Meningitis
2. Pneumonia
3.Endocarditis
4.Pyelonephritis
5. Biofilm on medical devices
Toxin-mediated
1. TSS
2. Necrotizing pneumonia (PVL)
3. SSSS (exfoliative toxins)
4. Food poisoning (enterotoxins)

Question 8

Staph tube coagulase test procedure

Answer 8

1. emulsify 1 colony of test organism in 1ml rabbit plasma.
2. Incubate at 37C overnight.
   Pos = visible clot formation or lose web of fibrin.
   Neg = No clot.

Question 9

Staphaurex Plus kit procedure

Answer 9

1. Bring latex to room temp + mix by vigorous shaking.
2. Dispense one drop of test latex onto one circle and one drop of control on the other.
3. Using loop, pick up and smear equivalent of 5 colonies onto circle + mix.
4. Spread to cover circle.
5. Rock card for 20 s.
6. Observe for agglutination.
   Agglutination within 20s = S. Aureus
   No agglutination = Coagulase-neg. Staph.

Question 10

Staph DNase test procedure

Answer 10

1. Divide DNA agar plate into 3
2. Spot inoculate test on 1 half (10mm) and controls (pos = S.Aureus, neg = S.epidermidis) on other half.
3. Incubate at 37C overnight.
4. Following incubation, in fume hood flood plate with 1M HCl and allow acid to permeate for 10 mins and carefully pour off excess into discard jar.
   Pos = distinct clear zones around inoculum = Staph Aureus
   Neg = S. epidermidis.

Question 11

Staph Mannitol Salt agar + SAIDE agar test procedure + results

Answer 11

1. Using streak-inoculation, sub-culture test organisms + controls (SA, SE) isolates on MS agar and SAIDE agar
2. Incubate overnight at 37C.
   S.Aureus = growth + fermentation on MS (Pink -> Yellow) + growth on SAIDE.
   S. epidermidis = growth + no fermentation on MSA (Pink) + no growth on SAIDE.

Question 12

Staph Aureus food poisoning

Answer 12

Enterotoxin
Acute onset 2-6hrs
Severe nausea + vomiting + abdominal pain + diarrhea
Self-limiting 8-24hrs
If disseminates to blood can cause TSS

Question 13

Staph aureus food poisoning sources

Answer 13

Food prepared by handlers + no additional cooking
-salads, ham, egg, tuna, chicken, potato,
- dairy products + milk
- Bakery (cream pastries)
- sandwiches

Question 14

Staph epidermidis infections

Answer 14

1. Device associated infections - IV, feeding lines, catheters, implanted prosthetic devices.
2. HCAI bloodstream infection.

Question 15

Staph saprophyticus infection

Answer 15

1. UTIs in sexually active young females

Question 16

Staph specimens

Answer 16

Skin swab, pus specimen, wound swab, blood, sputum, urine

Question 17

Additional confirmatory tests Staph Aureus

Answer 17

1. VITEK GP card = extra biochemical tests
2. MALDI TOF = protein profile
3. PCR = Xpert MRSA/ SA assay - target Protein A (SA) or mecA (MRSA) DNA sequences.

Question 18

Staph aureus - what to do if clinically significant

Answer 18

AST + Treatment
No resistance = methicillin
MRSA = vancomycin

Question 19

Staph aureus superficial infection treatment

Answer 19

Topical = Mupirocin
Oral = Augmentin

Question 20

S epidermidis infection treatment

Answer 20

Vancomycin
If MRSA = oxacillin + rifampcin
Skin infection = Fucidic acid

Question 21

S. Saprophytic infection treatment

Answer 21

UTI - Nitrofurantoin