Liquid Baird-Parker Medium

LAB 158

Description

Developed by Van Doorne et al in 1981, this medium is essentially Baird-Parker Agar LAB 085 without the agar and egg yolk components. This medium was chosen for development to overcome the problems of other selective enrichments and non-selective enrichments, in the isolation of Staphlococcus aureus.

Other selective broth media suffer from the potential of inhibiting sub lethally damaged S. aureus cells where the salt content is greater than 40g/l. Even Giolitti Cantoni Medium may be inhibitory to some strains of S. aureus.

Non selective enrichments have been suggested, but are not ideal due to potential inhibition of S. aureus by microbial antagonism in a mixed bacterial population.

Liquid Baird-Parker Medium is the ideal solution for detecting low numbers (<20/g) of S. aureus as it has been shown to give acceptable selectivity whilst being non-inhibitory to injured cells.

Method for reconstitution

Weigh 13 grams of powder, disperse in 1 litre of deionised water, heat to dissolve then distribute into bottles with Durham tubes. Sterilise by autoclaving at 121˚C for 15 minutes.

Appearance: Straw coloured, clear.

pH: 6.9 ± 0.2

Minimum Q.C. organisms: E. coli NCIMB 50034

Method for Reconstitution

Double Strength Medium: Weigh 86 grams of powder and disperse in 1 litre of deionised water. Soak for 10 minutes, mix to dissolve and dispense 10ml amounts in tubes. Sterilise at 121˚C for 15 minutes. Before use, heat to 100˚C in a water bath or steamer for 15 minutes to remove oxygen, cool and add 0.2ml of 1% potassium tellurite solution to each tube.

Single Strength Medium: Weigh 43 grams of powder and proceed as above. When cool, add 0.1ml of 1% potassium tellurite solution to each tube.

Appearance: Clear straw broth.

pH: 6.8 ± 0.2.

B 50080 NCIMB 50034

Storage of Prepared Medium: Capped containers - up to 3 months at 15-20˚C in the dark.

Inoculation: See methods for standard techniques.

Incubation: 35˚C aerobically for 48 hours.

Interpretation: Coliforms are presumptively identified by their ability to ferment lactose and produce gas within 48 hours at 35˚C.

References

American Public Health Association. (1975). Standard Methods for the examination of water and waste water, 892. Washington. United States Pharmocopeia, XXI, 1985.

Storage of prepared medium: Up to 1 month at 2-8˚C (without tellurite added).

Inoculation: Double strength; 10ml of sample homogenate to each tube. Single strength; 1ml of sample homogenate to each tube.

Incubation: 37˚C anaerobically for 48 hours. Anaerobic conditions can be achieved using an anerobic jar (container caps must be loose fitting) or by overlaying the surface of the broth with 1cm of molten agar or liquid parafin.

Interpretation: Culture tubes showing growth (blackening of the medium and turbidity) onto Baird-Parker Agar LAB 085.

References

Va n Doorne, H., Baird, R.M., Hendriksz, D.T., Van der Kreek, D.M., Pauwels, H.P. (1981) Liquid Modification of Baird-Parker's Medium for the Selective Enrichment of Staphylococcus aureus. Antonie Van Leeuwenhoek 47 267-278.