Physical Indicator: Sterilizing filters are subjected to a bubble point pressure test. This is a technique for determining the pore size of a filter, and may also be used to check the integrity of certain types of filters. The principle of the test is that the wetted filter in its assembled unit is subjected to an increasing air or nitrogen gas pressure difference. The pressure difference recorded when the first bubble of gas breaks away from the filter is related to maximum pore size.
Biological Indicator: The test effectively measures the
ability of a filter to produce a sterile filtrate from a culture of suitable
organism S. marcescens, a small gram-negative rod-shaped bacterium. B. diminuta
used as a biological indicator having a dimension of 0.5 micrometer and 0.3
micrometer respectively has been used for filters of 0.45 micrometer and 0.22
micrometer (Table).
Table: Indicators in filtration sterilization
|
Indicator |
Sterilization Method |
Principle |
Device |
Parameter monitored |
|
Physical |
Filtration
sterlization |
Forcibly
passing of solution through the membrane |
Bubble point
pressure test |
Pressure |
|
Biological |
Filtration
sterlization |
Retention of
bacteria |
B. diminuta |
Size of
microorganism |