minute particles of bacterial cells that pass through the pores of bacterial filters when liquid bacterial cultures are filtered.
There are many species of sporogenous and nonsporogenous bacteria, such as cocci and Mycobacteria. Nutrient media rich in organic matter are needed for their growth. When the filtrate culture is placed on a solid medium, filterable bacteria produce minuscule colonies. If these colonies are placed next to large colonies of cultured bacteria that release stimulating substances into the medium, the development of the colonies of filterable bacteria is promoted, a procedure known as the feeding method. When transferred to another medium, filterable bacteria may retain their own size and shape, as well as the characteristics typical of their colony. On the other hand, they may acquire the morphological and physiological properties of the bacterial culture from which they were derived.
Filterable bacteria are apparently minute, defective filterable particles of bacterial cells in a culture; it is unlikely that they constitute a developmental stage in the life cycle of bacteria. Filterable bacteria are not the same as the minute or infinitesimal bacteria whose cells pass through bacterial filters, for example, bacteria of the genus Mycoplasma, some spirochetes, and the causative agent of pleuropneumonia.
A. A. IMSHENETSKII