The effect of filters on aseptic pipetting lifetime of mechanical and electronic pipettors and carryover during pipetting

The aseptic pipetting lifetime of air displacement pipettors during serial pipetting was investigated. When a Micrococcus luteus(T) culture was pipett ed using no filter, less than 100 pipettings were required to contaminate t he interiors of both mechanical and electronic pipettors with more than 10( 3) cfu (n = 1890 pipettings). When a filter was placed in the pipettor tip cone, the sterility of the pipettor barrel was maintained for more than 500 pipettings (n = 2620) or 50-250 pipettings (n = 2520), depending on the fi lter type used. When a radioactive liquid or plasmid DNA was pipetted using no filter, contamination of the pipettor barrel occurred within less than 100 pipettings. A filter placed in the pipettor tip cone protected the inte rior of the pipettors against radioactive contamination for more than 250 p ipettings and against DNA contamination for more than 500 pipettings. A pip ettor barrel contaminated with M. luteus(T) caused carryover in 13% of the pipetting series. When a SCF filter was placed in the tip cone, no carryove r was observed within 2620 pipettings. A tip cone filter replaced at interv als of 50-250 (polyethylene filter) or 500 (SCF filter) pipettings will pro tect the pipettor barrel from contamination and the samples from carryover.