Laboratory apparatus for collection of flocculated vegetative bacterial cells.

Recent observations by Hodge and Metcalfe (1957) have demonstrated the ability of a number of hydrophilic colloids to flocculate cells of various bacterial species. Flocculation of the cells occurred by a mechanism previously proposed by Michaels (1954); namely, adsorption of the flocculant on the hydrated surface of the colloid particle, and a bridging between the suspended particles. In general, it may be said that a phenomenon applicable to a number of bacterial organisms has been discovered, and that several different colloidal substances display this phenomenon. Thus, it is possible to collect by a physiochemical method cells in quantities usually secured only from centifugation. Cell masses collected by flocculation, in contrast to cells collected by centrifugation, can readily be made into uniform suspensions of infinite dilution. Cells collected by the use of hydrophilic colloids may have other desirable characteristics differing from centrifuge-collected cells. To make use of these observations, efficient collection vessels must be developed. Such vessels should not require a volume of culture greater than can readily be produced in the laboratory and should collect essentially all cells present in the culture and concentrate them to a significant degree. This report describes several designs of vessels tested for collecting cells of Brucella suis using 2 per cent gelatin as the flocculant. When appropriate to the designs, the effects of vibration and angle of incline of the surface onto which the cells precipitate were tested. The effect of certain other variables on collection were determined and a method for establishing the rate at which flocculated cells move on these surfaces is presented.