Baird-Parker Medium Base

LAB 85

Description

Baird-Parker introduced this complex medium in 1962 to overcome the problems of recovering damaged Staphylococcus aureus from foodstuffs. The medium is highly selective due to potassium tellurite and lithium chloride. The tellurite inhibits most coliforms and is also reduced by S. aureus to telluride giving typical black colonies. Glycine and sodium pyruvate are both utilised by staphylococci as growth factors, pyruvate also neutralises toxic peroxides that may be formed in the medium. Sulphamethazine may be added to inhibit Proteus spp. The typical reactions of S. aureus are detected by the egg yolk emulsion: (1) lecithinase production - an opaque zone round the colony; (2) lipase production - a zone of clearing outside the opaque zone.

Colonies suspected of being S. aureus should be confirmed by the coagulase test or by a latex agglutination kit.

Alternatively the base medium can be used with the RPF (Rabbit Plasma Fibrinogen) supplement (X086). This supplement is a more specific alternative to Egg Yolk Tellurite Emulsion (EYT) for the direct detection of coagulase positive S. aureus. The use of the RPF supplement overcomes several disadvantages of EYT: (1) S. aureus isolates on traditional Baird-Parker Medium have to be confirmed with a separate coagulase reaction, (2) S. aureus does not always give typical egg yolk reactions.

Method for reconstitution

Weigh 65.5 grams of powder, disperse in 1 litre of deionised water. Allow the medium to soak for 10 minutes, swirl to mix then sterilise by autoclaving at 121°C for 15 minutes. Cool to 47°C and add 50ml of X085 sterile egg yolk tellurite emulsion. Mix well and dispense into Petri dishes.

For Baird-Parker RPF medium

Weigh 5.9 grams of powder and disperse in to 90ml of deionised water. Allow the medium to soak for 10 minutes, swirl to mix then sterilise by autoclaving at 121°C for 15 minutes. Cool to 47°C and add 1 vial of X086 RPF supplement. Mix well and pour into Petri dishes.

Appearance: Cream/pale fawn, opaque with X085. Translucent, pale straw with X086.

pH: 6.8 ± 0.2

Minimum Q.C. organisms: S. aureus NCIMB 50080

S. epidermidis NCIMB 50082 E. coli (inhibition) NCIMB 50034

Storage of Prepared Medium: Plates - up to 3 days at 2-8˚C in the dark.

Inoculation: Surface spread.

Incubation: 37˚C aerobically for 48 hours.

Growth characteristics(with X085)

Entero-         no growth

bacteriaceae

Growth characteristics(with X086)

Method for reconstitution

Agar Base ‘A': Weigh 36.4 grams of powder and mix with 1 litr deionised water. Sterilise for 15 minutes at 121˚C. Cool to 5 approx. and add 100ml of Chemical Mixture ‘B'. Mix well and p thin plates. Store at 4˚C for 3 days to mature, before use.

Chemical Mixture ‘B': Suspend 18 grams of powder in 10 of deionised water. Bring to boil over a tripod and gauze, and c quickly in cold water. Add to 1 litre of Agar Base ‘A' prepa as above.

Appearance: Pale green, opaque gel.

pH: 7.6 ± 0.2

References

Baird-Parker, A.C. (1962). An improved diagnostic and selective medium for isolating coagulase positive staphylococci. J. Appl. Bact. 25(1): 12-19.

Baird-Parker, A.C. and Davenport, E. (1965). The effect of Recovery medium on the isolation of S. aureus after heat treatment and after storage of frozen or dried cells. J. Appl. Bact 28: 390-402.

Ten Broeke, R. (1976). The Staphylococcus medium of Baird-Parker in practical use. The occurrence of coagulase-positive, egg yolk non-clearing staphylococci. Antonie van Leeuwenhoek 33: 220-236.

Smith, B.A. and Baird-Parker, A.C. (1964). The use of sulphamethazine for inhibiting Proteus spp. on Baird-Parker's isolation medium for Staphylococcus aureus. J. Appl. Bact 27(1): 78-82.

Beckers N J. et al (1984). Canad. J. Microbiol. 30: 470-474.

Sawhney D. (1986) J. Appl Bact. 61:149-155.