Studies on the Microbial Growth

Part 4. The Methods for Determining the Viable Count of the Bacteria

Abstract

The viable counting of the bacteria was studied by the plating and “capillary tube methods”^* examining especially (1) the using technic of the pipette, (2) the distribution type of the pipetting error, (3) the error in the tube counting and (4) the comparison with the hemocytometer method. The results were as follows: (1) Between the colony counts obtained by the consecutive uses of the same pipette from the same bacterial suspension, there are no significant differences (Table 1). But, when the dilution of the bacterial suspension is performed by the repeating uses of the same pipette, the colony counts increase in proportion to the times of repeating uses. (2) In the cases of plate and tube countings, it has been shown that the errors of viable counting which is due to pipetting, distribute generally in Poisson type (Fig. 1 and Fig. 2), and when the mean count is large (more than 30), it can be allowed to say that the error of the counting distribute approximately in Gaussian type (Fig. 3). (3) In the analysis of the error variance of the tubecoun-ting, the variances between dilution series show no significant differences (Table 2). (4) Mean counts obtained by the hemocytometer and tube counting from the same bacterial suspension, are shown in Table 3. As to the mean counts and variances, there are no significant differences between the plating and capillary tube methods (Table 4).
*The “capillary tube method” have been named by T. Yanagita and H. Tamiya (University of Tokyo) and here the viable counting by this method is called the tube counting.