Fluorescence Agar

LAB 16

Description

This medium is a modification of King, Ward and Raney's medium formulated for the demonstration of the fluorescein pigment produced by many strains of Pseudomonas. The pyocyanin pigment produced by most strains of Pseudomonas aeruginosa is also produced. Can be made selective by the addition of selective agents such as X108 Cetrimide Fucidin Cephaloridine.

Method for reconstitution

Weigh 35 grams of powder, disperse in 1 litre of deionised water containing 10ml Glycerin B.P. Allow to soak for 10 minutes, swirl to mix then sterilise for 15 minutes at 121˚C. Mix well before pouring. Slant over a generous butt if required.

Appearance: Straw coloured, clear gel.

pH: 7.2 ± 0.2

Minimum Q.C. organisms: Ps. aeruginosa NCIMB 50067

Storage of Prepared Medium: Plates - up to 7 days at 2-8˚C in the dark.

Inoculation: Surface spreading.

Incubation: 30-37˚C for 24 and 48 hours aerobically.

Method for reconstitution

Weigh 55 grams of power and add to 1 litre of deionised water (add to 900ml if preparing 1/2 Fraser). Allow to soak for 10 minutes, swirl to mix and sterilise at 121˚C for 15 minutes. Cool to 47˚C and add 2 vials of Fraser supplement X165 (or 2 vials of 1/2 Fraser supplement X164), mix well and aseptically dispense into sterile tubes or bottles.

Appearance: Straw opalescent broth with precipitate (clears on storage).

pH 7.2 + 0.2

Minimum Q.C. organisms: Listeria sp NCIMB 50007 e. coli (inhibition)

Storage of Prepared Medium: Bottles - up to 14 days at 2-8˚C.

Inoculation: 1/2 Fraser - Add 25g sample to 225ml of 1/2 Fraser broth and homogenise Fraser - Subculture 0.1ml of primary enrichment broth (UVM I or 1/2 Fraser) into 10ml of Fraser broth.

Incubation: 1/2 Fraser - 30˚C aerobically for 24hrs.

Fraser - 35˚C aerobically for 24hrs and 48hrs. Subculture onto selective agars at 24 and 48hrs.

Interpretation

Blackening of the broth indicates the presence of a potential Listeria and should be subcultured onto Listeria isolation medium (Oxford) LAB122 or Palcam agar LAB148. All broths should be subcultured before discarding, irrespective of colour change.

References

Fraser J.A., and Sperber W.H., (1988) Rapid detection of Listeria spp in food and environmental samples by esculin hydrolysis. J.Food Protection 51 (10) 762-765.

McClain D., and Lee W.H. (1989) FSIS method for isolation of L.monocytogenes from processed meat and poultry products. Lab.Comm.No.57, Revised May 24, (1989). US Dept of Agric.FSIS, Microbiol. Div.