Keeping Things Clean

There are tiny living things all around us, in the air we breathe, on every surface we touch, and even all over our own bodies. The challenge we face with growing mushrooms, or any kind of culture work for that matter, is trying to isolate and grow just the single specific organism we want, and not the random assortment of bacteria and mold in our environment.

Should be easy enough, the local grocery store has everything from antibacterial hand soap to spray cleaners that "kill 99.99% of bacteria", but these marketing claims aren't all they're cracked up to be. Antibacterial hand soap, for example, doesn't contain any special chemical compound to kill bacteria, its claim is simply based on the surfactant properties of soap, when used with water, to wash bacteria off of your hands and down the drain. This is still a good thing to do, but it isn't a magic bullet for achieving sterile hands by any means.

Its important to recognize the difference between sanitizing and sterilizing, as they are not the same thing. Sanitizing reduces living microorganisms on a surface to a safe level; the "99.99%" claim that you see on Lysol fits into this category, and do isopropyl alcohol, peroxide, and bleach. These methods are less effective for killing viruses and spores, and achieving the 99.99% isn't as simple as just spraying it on a surface and wiping it with a paper towel, but requires the chemical agent to sit on the surface in a liquid form for an extended amount of time to be fully effective. As for that effective percentage thing: there can be 10,000,000 bacteria on a square inch of a kitchen dish sponge...after killing up 99.99%, there's still at least 1000, and it only takes one to start repopulating.

Sterilizing eliminates all microorganisms, both living and in spore form, but requires a much more intense process. We accomplish this with high heat, by flame sterilizing our scalpel blade or inoculation loop until its glowing red hot, or with a combination of heat and time to sterilize media like agar or grain spawn. Its just not feasible to do this to our table tops or lab spaces, and certainly not our own bodies.

We fully sterilize our growing media to ensure that the only thing growing on it is what we want to grow, but these clean nutrient sources are very inviting to any contamination that might get into them, and this is where sterile technique comes into play. While its good to have a clean work area, it isn't necessary or even possible to kill everything in the environment. Sterile technique is a matter of simply not adding contaminants to our media by physical means.

Air movement, or the lack thereof, is one of the primary tools for preventing airborne contamination. A still air box (SAB) helps control air currents and reduces particulates by trapping them in soapy water sprayed on the insides of the box and a moistened towel on the bottom Moving air solutions include flow hoods, which force air through a very low micron hepa filter, and also convection methods like an alcohol lamp or the "oven door" method, where a localized heat source causes air to rise and lifts any airborne contaminants up and away from the work.

Careful deliberate movements help reduce the chance of introducing contaminants. Its important to only open sterile media long enough get what you need in or out of it. Hands fumbling above an open petri dish is a good way to drop something unwanted into it, with or without gloves. And speaking of gloves, while they can limit bacteria shedding from your skin, they can just as easily transfer contaminants from anything else you touch while you're wearing them. Having all the materials and tools you need staged in a logical fashion in your workspace helps limit the need to touch things unnecessarily.

In a still air environment, its important to avoid being above your sterile media, and to move very slowly so as not to stir up air currents. With moving air you can move about more freely, but have to remain cognizant of the directional air; the sterile media should always be upwind of your hands so it doesn't blow things into your work. The flame sterilized end of the scalpel or inoculation loop should be the only part that enters the petri dish or grain jar, your fingers holding the handle should always remain outside the rim of the container. This can sometimes be facilitated by tilting the dish or jar so you're approaching the entrance from the side rather than from above.

Learning sterile technique is a process, requiring practice and often a good amount of making mistakes to really master it. Mold and bacteria are incredibly easy to grow...messing up sterile technique can be frustrating and costly in terms of time and materials, but also presents opportunities to learn how to recognize different types of contamination, and this helps improve your efficiency down the road. Having a clean workspace helps to reduce risks of contamination, but being obsessive with chemical agents trying to kill everything isn't as effective as mastering sterile technique; even if you kill 99.99% of everything, you can still put that 0.01% into your work if you're not careful, and it will be just as contaminated as if you hadn't choked your household with Lysol fumes.