Answer by Dr. Jessica Wagener, Application Specialist Cell Handling at Eppendorf
This article appeared first in “Inside Cell Culture”, the monthly newsletter for cell culture professionals
In most CO2 incubators a simple tray filled with sterile distilled water is placed in the incubator to generate a highly humid atmosphere inside. This atmosphere prevents the cultured cells from drying out over time. Unfortunately, a humid atmosphere is also favored by unwanted microbial contaminants. However, adding biocides to the water of the humidity tray should be considered carefully. One aspect is the corrosive potential of some antimicrobial reagents, which can damage the stainless-steel of the humidity tray. Another risk is posed by volatile compounds in these reagents that might influence cell growth after evaporating from the humidity tray.
Independently of the use of antimicrobial reagents, the water in the humidity tray should be monitored closely to avoid undetected contamination growth or accumulation of harmful substances. Instead of only refilling the water it is advisable to completely replace the water regularly and clean the humidity tray (e.g. with 70% Ethanol) before adding fresh water. Our general recommendation is to replace the water in the CO2 incubator once a week.