Problems in standardization of turbidity determinations on bacterial suspensions.

The concentration of bacterial suspensions can be rapidly and conveniently determined by measuring the turbidity. Although turbidimetry offers advantages over the more laborious methods of weighing or counting, it is necessary to be aware of the possible sources of error. It is therefore advisable for every type of instrument used to specify, in terms of the International Opacity Reference Preparation, the turbidities of known suspensions of the organisms under study. Only bacterial suspensions having the same extinction coefficient can be adjusted to the same content of bacteria by means of the International Opacity Reference Preparation.