Bacterial contamination of drops and dropper tips of in-use multidose eye drop bottles

The type and frequency of bacterial contamination of 638 in-use multidose eye drop bottles are reported. By dripping, bacteria were recovered from 82 bottles (12.9%). Bacterial growth considered to be clinically and microbiologically significant were found in 12 cases (1.9%). The swabbings from 38 of 180 dropper tips (21.1%) yielded bacteria, while none of the pipette aspirates from 196 bottles were positive. The flora obtained by dripping and swabbing was very similar to the normal conjunctival and skin flora. It is suggested that microorganisms isolated by dripping often originate from contaminated dropper tips. The frequency of contaminated drops did not increase with increasing duration of use of the bottles. Repeated examinations and inoculation studies indicated that the solutions were self-sterilizing. This indicates that multidose eye drop bottles preserved and dispensed as in the present study may be used for more than the usual 4 weeks without increasing the risk of ocular infection.