On the Filtrability of Bacteria.

Abstract

The statement has been made that filtrates, presumably sterile, prepared from lysed cultures of various bacteria sometimes yield, on standing, a visible growth. The growth so obtained has been interpreted as pointing to a filtrable stage in the life cycle of the bacteria employed. 1 , 2

We have followed for a period of three years lysed cultures of different bacteria, and have watched for the appearances mentioned. On the basis of our studies we have concluded that all such secondary growths are the results of accidents due to imperfection of the filter itself, or to faulty technique employed in carrying out the filtration process. We have recently subjected comparatively large amounts of lysed cultures to fractional filtration through new candles, and noted that while the first several fractions of the filtrate came through wholly sterile, the later fractions often yielded growths.

The number of bacteria which may pass the filter in this way is too small to be detected by the ordinary subculture control; but when entire fractions of the filtrates are incubated, the gradual lessening of the efficiency of the filter, which now permits organisms to pass, is shown. Probably the breakdown of the filter is attributable to the coating of the surface with the colloids of the culture medium and distribution of the charge on its particles.