1. Maintenance and Use of Stock Cultures
Stock cultures are used in Internal Quality Control.

2. @ Stock culture strains are obtained from :
isolates from clinical specimens
official culture collections
reference laboratories
external quality assurance surveys
commercial distributors

3. Maintenance of stock cultures is made by:
@ long-term or short-term preservation.

4. Long-Term Preservation
@ This gives months or years between subcultures.

5. @ The best methods are : Lyophilization (freeze – drying)
2.Storage below – 70˚C in :
a freezer
in liquid nitrogen.

6. 3.Glycerol at -20˚C. * Proceed as follows:
Grow a pure culture on a solid medium
Scrape culture off with a loop
Suspend growth in neutral glycerol

7. Distribute in screw-capped tubes
Store at -20˚C
Avoid repeated freezing & thawing
Subculture after months.

8. 4.Stab cultures for non-exacting organisms
* Proceed as follows:
Prepare tubes with a deep butt tryptic soya agar
Stab organism into the agar

9. Incubate overnight at 35˚C
Close tube with screw-cap
Dip cap into molten paraffin to seal
Store at room temperature
Subculture after one year.

10. 5.Stab cultures for exacting organisms
* Proceed as follows:
Prepare tubes of cystine trypticase agar
Stab organism into the medium
Incubate overnight at 35˚C

11. Close tube with screw-cap
Seal cap into molten paraffin
Neisseria store at 35˚C & subculture every 2 weeks.
Strep. store at room temp. & subculture monthly

12. 6.Cooked meat medium for anaerobes:
* Proceed as follows:
Inoculate tubes

13. Incubate overnight at 35˚C
Close tube with screw-cap
Store at room temperature
Transfer every two months

14. Short-Term Preservation
@ This is used for daily routine work .

15. @ For rapidly growing organisms
* Proceed as follows:
1.Inoculate a tryptic soya agar slant in screw-capped tubes

16. 2.Incubate overnight at 35˚C
3.Store in refrigerator
4.Subculture every two weeks

17. For streptococci 1.Inoculate a blood agar slant in screw-capped tubes
Proceed as follows: :
1.Inoculate a blood agar slant in screw-capped tubes

18. 2.Inocubate overnight at 35˚C
3.Store in refrigerator
4.Subculture every two weeks

19. @ For meningococci & Haemophilus
Proceed as follows:
1.Inoculate a chocolate agar slant

20. 2.Incubate overnight at 35˚C
3.Store at room temperature
4.Subculture twice a week

21. @ For gonococci 1. Inoculate on CBA 2. Incubate and store at 35˚C
Proceed as follows:
1. Inoculate on CBA
2. Incubate and store at 35˚C

22. 3. Subculture every two days
4. Replace the QC strain by each new clinical isolate