Division 2.1.3 F1

If required, the bacterial fraction may be concentrated using one of the following methods:

1. (a)

   Centrifuge 30 to 50 ml sub-samples at 10 000  g for 10 minutes (or  7 000  g for 15 minutes) preferably at 4 to 10 °C, discard the supernatant and resuspend the pellet in 1 ml pellet buffer (Appendix 4).

2. (b)

   Membrane filtration (minimum pore size 0,45 µm) followed by washing the filter in 5 to 10 ml pellet buffer and retention of the washings. This method is suitable for larger volumes of water containing low numbers of saprophytes.

Concentration is usually not advisable for samples of potato processing or sewage effluent since increased populations of competing saprophytic bacteria will inhibit detection of Ralstonia solanacearum .