One of the most exciting aspects of being a biologist is getting opportunities to examine how and why living organisms behave the way they do. We have technology that enables us to obtain images at sub-cellular levels, and the skills to work directly with the micro-environments essential for the progression of life.
However, at the end of the day, when all of the tissue and blood samples have been processed, what is left behind?
The answer is a tissue culture hood that is simply festering with potential contamination. We must keep in mind that while aseptic technique and daily wipe downs diminish the majority of contaminant growth, they are not the final line of defense. This article describes the extra steps necessary to ensure that your tissue culture hood is sterile on the deeper levels.
Time to break it down
If you share a tissue culture facility with other researchers, a few months of work can easily expose every surface to countless contaminants. Furthermore, despite the lab’s best efforts to sterilize the environment, it must be noted that tissue samples can be quite robust, and micro-organisms such as bacteria, fungi, protists and viruses have a strong will to survive and multiply. Therefore, at least twice a year, the biosafety cabinet should be disassembled and cleaned deep within. In my experience, this is a lot more pleasant if you do it with a couple of lab friends.
To begin the deep clean, disinfect any items that are kept in the hood and remove them (e.g. pipet tip boxes or waste containers). Next, you need to take the hood apart. Depending on the manufacturer, the work area can be broken down by either unhooking and sliding out the surfaces, or using a screw-driver to release the four corners (check the manual for the proper way to disassemble the hood). Whichever way, the goal is to take out every removable work surface within the hood and expose the hidden drip tray underneath. The tray area is where airflow manages to trap debris and spilled materials as they are pulled toward the HEPA filter. Given that it has probably been several months since anyone has peeked down there, the probability of something nasty growing on the surface is very high.
If you would not eat off of it, then it is not clean
Now that the fun of disassembling that pesky cabinet has come to an end, the actual work begins. Everything needs to be scrubbed; the removable pieces as well as the inside of the hood.
First remove any consumables that are hidden in the underlying spaces of the hood; random pipette tips and plastic PCR plate seals always seem to find their way down there.
Second, scrub out the hood with a mild detergent using a sponge or wads of paper towels. Likewise, bring all removable pieces to a sink and scrub those down. Normally, when sterilizing a work space, you would use a disinfectant such as Virkon followed by a good scrubbing with a 70% alcohol solution. However, when deep cleaning, this is not true. Disinfectants such as Virkon contain substances such as bleach or chlorine that can damage the metal if not removed thoroughly. My recommendation is to simply use soap and water on the surfaces at this point.
Third, autoclave all of the removable parts. This is when your Tetris skills come in handy: figuring out how to fit those pieces in the autoclave is a puzzle. Make sure the pressure and temperature of the autoclave are adequate to nullify the specific contaminants that your lab uses on a regular basis.
Fourth, reassemble the autoclave (you might want to make sure the removable pieces are cool first!). When you are putting the hood back together, this is a good time to replace some items such as hoses for a vacuum trap, filters and the UV lamp. Once everything is back together, wipe the clean surfaces with your usual disinfectant followed by alcohol, close the sash (you cleaned this too, right?) and turn on the UV.
Get the sticker
Things are going well, the visible rubbish was thrown out, all detachable surfaces have been autoclaved, and reassembly has been successfully completed. Everything should be good to go for the next researcher, right? Well, there is one other thing that needs to be done for hoods on a yearly basis: certification. Hoods need to be certified annually to make sure they are functioning appropriately. Timing this with the hood cleaning is a great way to make sure you assembled all parts of the hood correctly. The technician will certify that the airflow in the hood is up to spec and place a validation sticker on the hood indicating when it should be inspected again.
Cleaning the hoods can pull you away from valuable bench time. But if everyone in the lab works together, the amount of down time will be greatly decreased. After all, in a lab, sterility is only as strong as the weakest decontamination efforts.