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During times of high concentrations of airborne particulates, such as in the spring during pollen season and during construction when dust and dirt is created, there is a statistically higher chance of having contamination due to airborne spores and other microorganisms associated with the dust and the airborne particulates. I thought it might be helpful for us to alert our users of this potential and make some recommendations about what can be done to try to reduce the risk.
- Have the air flow rate in your hood(s) checked. As HEPA filters load over time, the pressure drop will increase and the flow rate may be reduced to levels below the rate required for the stability of the laminar flow. If this happens, there is a higher likelihood that air turbulence within the cabinet will occur during a manipulation that could lead to contamination from an airborne source. The air flow rate should not be less than 80-85 feet per minute. UNC Health and Safety has an anemometer and can check this for you or the TCF can recommend a third party vendor.
- Reduce traffic in your cell culture rooms, especially near the hoods. Traffic causes air turbulence at the hood opening and can compromise the protective air barrier that is created by the downward flow of air inside the cabinet at the opening. Spore-carrying dust particles or other airborne contaminates could get into the working area and ultimately find their way into your media or cultures.
- Do not use flames (bunsen burners, etc.) under the hood. This will cause air turbulence over the flame and in the working area that could lead to spores from your lab coat, for example, being caught up in the turbulence and blown into your media bottle, flask, or, dish, etc. All routine cell culture manipulations can be done without flaming by using appropriate aseptic and sterile technique. We will be glad to offer specific suggestions and training regarding this if necessary.
- Make sure all interior hood surfaces are adequately disinfected, preferably by using chemical disinfectants such as 70% ethanol, dilute hypochlorite, or a dilute quaternary ammonium solution such as 1% benzalconium chloride. Freshness of the solutions and adequate contact time are important for these to work properly.
- Consider using TC flasks with vented filter caps instead of flasks that require loosened caps for gas exchange or dishes. These flasks tend to reduce airborne contamination and especially the spread of contamination from one vessel to another while in the incubator. These flasks are more costly but it may be worth the extra cost considering the higher risk at this time. At least you may consider using them for stock cultures or for extremely important cultures.
- If you experience chronic contamination problems, you may want to consider using an antibiotic (with an anti-mycotic component for fungal or yeast problems). Whereas I don't recommend them for routine use, sometimes they may be necessary in certain situations or in areas with unusually high concentrations of airborne particulates. We can make specific recommendations as to which antibiotics to use and at what concentrations. Please note that pen/strep offers no protection against fungus.
- It may be useful to monitor the airborne microbial levels in your cell culture rooms and even within your hoods (it should be 0 in hoods) by using Nutrient Agar and Sabouraud Dextrose Agar plates. Nutrient agar will give you information about airborne bacteria levels and Sabouraud dextrose agar will detect airborne fungi and spores. Put plates at various locations in the lab and in your hood. Take the lids off for a set period of time, 30 minutes for example. Collect the plates and incubate the nutrient agar plates for 3 to 5 days and the Sabouraud dextrose agar plates for 7 to 10 days. Remember not to incubate these plates in incubators with your cell cultures! Take a total plate count and note the locations that seem to be high. Depending on what you find, there may be steps you can take to reduce the level of airborne contaminants.
I hope no one has serious problems, but if you do, please feel free to contact us at the TCF
if we can be of help. We will be happy to come to your cell culture lab and make specific recommendations and otherwise try to help with particular problems. We can also make recommendations regarding cleaning, preventive maintenance schedules, and disinfectants for hoods, water baths, and incubators.