Fastidious Anaerobe Broth (F.A.B.)

LAB 71

Method for reconstitution

Weigh 29.7 grams of powder, disperse in 1 litre of deionised water. Allow to soak for 10 minutes, swirl to mix. Boil to dissolve the agar then dispense into screw cap containers. Sterilise by autoclaving at 121˚C for 15 minutes. Tighten the caps as soon as possible after autoclaving.

Appearance: Pale straw, clear, viscous. May have a narrow band of red/purple at the surface due to action of oxygen on the resazurin. If the medium is reddish this indicates too much oxygen has been absorbed, the medium should be reheated to deoxygenate. Do not reheat more than once.

pH: 7.2 ± 0.2

Minimum Q.C. organisms: B. fragilis

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

Inoculation: If used as a blood culture medium a minimum dilution of 1:10 should be used.

Incubation: 37˚C for 24-72 hours. Keep the container airtight.

Growth indicators: The broth may become turbid or individual colonies may form suspended in the medium.

References

Gould, J.H., Duerden, B.I. (1983). Blood culture - current state and future prospects. J. Clin. Pathol. 36: 963-977.

Ganguli, G.A., O'Hare, W., Hyde, W.A. (1984). Rapid Detection of Bacteraemia by early subculture. J. Med. Microbiol. 17: 311-315.

Ganguli, L.A., Keaney, M.G.L., Hyde, W.A., Fraser, B.J. (1985). More Rapid identification of bacteraemia by manual rather than radiometric methods. J. Clin. Pathol. 38: 1146-1149.

Junt, G.H., Price, E.H. (1982). Comparison of a home made blood culture broth containing a papain digest of liver, with four commercially available media, for the isolation of anaerobes from simulated paediatoic blood cultures. J. Clin. Pathol. 35: 1142-1149.

Ganguli, L.A., Turton, L.J., Tillotson, G.S. (1982). Evaluation of Fastidious Anaerobe Broth as a blood culture medium. J. Clin. Pathol. 35: 458-461.

Tillotson, G.S. (1981). Evaluation of ten commercial blood culture systems to isolate a pryridoxal dependent streptococcus. J. Clin. Pathol. 34: 930-934.

Description

F.A.B. was developed by LAB M working in conjunction with the microbiology department of a University of Manchester teaching hospital. The medium was designed to give optimum growth of fastidious anaerobes and has found applications as a blood culture medium and an enrichment broth for the isolation of anaerobes. The medium is very rich in nutrients from the specially selected peptone mixture. Vitamin K. haemin and L-cysteine are all growth factors required by some anaerobes. L-cysteine together with sodium thioglycollate reduce the Eh of the medium and the agar content inhibits absorption of oxygen and convection currents. Resazurin is a redox indicator. Several published evaluations show F.A.B. to be the liquid medium of choice for fastidious anaerobes.