AN INEXPENSIVE SOLID MEDIUM FOR OBTAINING COLONY-FORMING-UNITS OF ORAL SPIROCHETES

A method for the enumeration of colony-forming units of oral anaerobic spirochetes in new oral spirochete agarose (NOS-A) medium was describ ed recently. However, the high cost of agarose limits the extent to wh ich large assays can be carried out. Accordingly, a search for an inex pensive gelling agent that remains molten at 37 degrees C and gels at 25 degrees C was undertaken. Varying amounts of Noble agar or Bacto ag ar (0.5 to 1.5%, w/v) were mixed with varying amounts of gelatin (0.5 to 1.0%, w/v) in NOS medium. NOS medium containing 0.5% gelatin-0.5% N oble agar (NOS-GN) or 0.5% gelatin-0.5% Bacto agar (NOS-GB) met the ab ove criteria. NOS-GN and NOS-GB media yielded higher colony-forming un its with Treponema denticola than NOS-A medium in that order. However, all three media, NOS-GN, NOS-GB and NOS-A, performed equally well in the recovery of viable counts of T. vincentii. The NOS-GN medium was n ot liquefied by subgingival bacteria or two gelatinase-producing speci es of bacteria, Bacillus subtilis and Staphylococcus aureus. Thus NOS- GN medium is the recommended medium both in cost and performance for o btaining colony counts of spirochetes.