1. Staphylococcus aureus
Staphyl: grape; coccus: round-shape
aureus: golden color
Presence of Staphylococcus aureus and/or its enterotoxins in processed foods or on food processing equipment is generally an indication of poor sanitation.
Human is the most common carrier.

3. Typical characteristics
Catalase
Coagulase
NaCl tolerance

4. Materials and methods Food: Food samples (sandwich) Sterile cotton
Bacteria:
Staphylococcus aureus
Human
Medium
Phosphate buffer saline (PBS)
TSB with 10% NaCl
Baird-Park agar
3% H2O2
Petri-film staphyl

5. Enumeration
25 g food sample (sandwich) is added into 225 mL of phosphate buffer saline. (x2)
Stomach for 2 min.
Inoculate S. aureus culture
1-6 groups, 1 mL of 10-4 overnight culture
7-11 groups, 1 mL of 10-5 overnight culture
MPN calculation
Incubate TSB-10% NaCl 24 hour at 37°C

6. 1 mL
TSB-10%NaCl
PBS
1 mL
1 mL
PBS
1 mL -3 -4 -1 -2

7. Barid-Parker agar
Typical colonies of S. aureus are black, shiny, convex and surrounded by clear zones (egg yolk reaction) of approximately 2-5 mm.
Pick up well-isolated colony for catalase test.

8. Biochemistry tests Catalase test:
Place a drop of 3% H2O2 on a glass slide
Positive reaction: gas generation
S. aureus: positive

9. Human test Wet a cotton stick in a phosphate buffer saline.
Use this cotton stick to swab both nose nasals.
Streak the cotton stick onto Baird-Parker plates.
Incubate the plates at 35-37℃ for 24 hour.
One plate/group

10. Difco™ Baird-Parker Agar Base
Approximate Formula* Per 950 mL
Pancreatic Digest of Casein g
Beef Extract g
Yeast Extract g
Glycine g
Sodium Pyruvate g
Lithium Chloride g
Agar g
Difco™ EY Tellurite Enrichment
Egg yolk emulsion containing potassium tellurite consists of 30% egg yolk suspension with 0.15% potassium tellurite.

11. Baird-Parker Agar Base contains peptone, beef extract and yeast extract as sources of nutrition.
Sodium pyruvate is incorporated to stimulate the growth of S. aureus without destroying the selectivity.
Tellurite is toxic to egg yolk clearing strains other than S. aureus and imparts a black color to the colonies.
Egg yolk additive, in addition to being an enrichment, aids in the identification process by demonstrating lecithinase activity (egg yolk reaction).
Glycine and lithium chloride have inhibitory action for organisms other than S. aureus.

13. Typical colonies of S. aureus are black, shiny, convex and surrounded by clear zones (egg yolk reaction) of approximately 2-5 mm.
Coagulase-negative staphylococci generally do not grow well; if some growth occurs, the typical clear zones are absent.

14. Pick up a well-isolated colony with typical characteristics with a loop
Suspend this colony in a 9 mL PBS by shaking the loop
Vortex the tube
Take 0.1 mL from the tube, then transfer into another 9 mL PBS tube, vortex
Drop one mL onto Petri-film
Incubate at 35-37℃ for 24 hour

15. Typical S. aureus
colonies on petrifilm

17. schedule 12/8 (Mon): prepare sample, TSB-10% incubation, human test
12/9 (Tue): streak onto Barid-Parker agar plates, (human) observe Barid-Parker plates and mark the typical colonies, store at refrigerator
12/10 (Wed) (food) Observe Barid-Parker plates and mark the typical colonies, store at refrigerator
12/15 (Mon): H2O2, petri-film, api test
12/16 (Tue): observe results