January 8, 2014
In the Lab: Testing Out a New Sterilizer
- Food Safety
By Lauren Bambusch
I am always on the lookout for the right lab equipment for a particular task. Since I often use a tool, device, or instrument daily, I want it to be reliable, easy to use, with little or no mandatory maintenance. The last thing I need is my equipment out of commission right when I need it most. I have found expensive does not necessarily mean more reliable — often simple (without all those bells and whistles) and inexpensive can be more dependable.
We are often asked by firms starting a new lab if they need a large expensive autoclave, so when our autoclave at InstantLabs began acting up, it created an opportunity to test a new approach. After doing our research we decided to try this simple and relatively inexpensive sterilizer to see if it could replace a more traditional autoclave like this one. We wanted to see if this relatively inexpensive unit could be a good fit for smaller laboratories or for firms setting up new labs with limited budgets.
After placing the order, the unit was delivered 2 days later. Now the fun begins — testing it to make sure it can it do the two key tasks we need it to do: make media and decontaminate waste.
My new toy: a drum sterilizer
Test Number One: Test the Sterility of Media that Comes Out of the Sterilizer
I mixed up 100 mL batches of both FASTGRO SE broth and Brain Heart Infusion (BHI) broth and inoculated them with 1 x 106 CFU/mL E. coli O157:H7 and Bacillus coagulans, respectively. These organisms were chosen to represent the heartiest organisms most likely to contaminate a batch of media, including the sporulating Bacillus. These batches were then autoclaved for 35 minutes at 121°C (approximately 250°F) and between 12 to 15 PSI, which are standard operating conditions for both autoclaves and sterilizers.
Once the sterilizer had run its cycle and cooled enough to be exhausted and opened, both media were allowed to cool and placed in a 35°C incubator for 5 days. The cultures were observed daily to check for any growth.
After 5 days, neither culture had recovered from sterilization, which indicates complete kill of a wide variety of organism types, even at high levels of contamination. The sterilizer had passed test number one.
Test Number Two: Decontamination of Waste
I created several lettuce and ground beef enrichments artificially contaminated with E. coli and Salmonella, then incubated them according to the respective InstantLabs protocol. After incubation, samples were taken and PCR was run according to the respective InstantLabs protocol to confirm adequate growth.
Now for the testing. I sterilized the enrichments at 121°C and 12-15 PSI (same as test 1) for 60 minutes. Once cooled, 100 µL sample were taken of each enrichment and spread onto a Nutrient Agar plate (pre-sterilization concentration equal to approximately 1 x 106 CFU/mL). These were then allowed to dry and were then incubated at 35°C for 4 days. The plates were checked daily for growth.
No growth was observed on any plate after 4 days of incubation, confirming complete decontamination of biohazardous waste. The sterilizer had passed test number two.
The Bottom Line
At $650, the price is a fraction of the average $3,500 you’d pay for a traditional autoclave of the same size. Even better, because it is mechanically less complicated, it is more reliable than your average automated autoclave. It is also easier to clean than your average automatic autoclave, which requires using a cleaner every 20 cycles and about a day of your time to run through the process. For the sterilizer, all you need to do is simply empty out the water, wipe down, and refill.
There are a few drawbacks to the sterilizer. It isn’t automated, meaning that you can’t just set it and forget it. You have to keep an eye on the temperature and pressure (which will become easier once you’ve used it a few times and get a feel for where on the dial your temperature sweet spot is). And once the timer goes off and the cycle is over, you have to manually turn off the machine. Also, the sterilizer gets hot. Quite hot. Make sure you don’t use your sterilizer on or around any materials you’re particularly fond of (I’ve already melted a small hole in the floor tiles). They do make a stand you can use to protect the surface it’s sitting on, but you still need to be careful about protecting any heat-sensitive reagents from the exhaust steam.
Overall, I’m quite happy with the machine. It’s a great cost-effective way to be able to make media and control your own waste without a lot of heartache. The 14.5 quart model can make 3.5 liters of media at a time (7 500 mL bottles) in a little over an hour, with plenty of room to spare for smaller equipment, as well. Aside from the optional stand that I thoroughly recommend, the only required accessory is a tube of lubricant for a complete seal between the drum and the lid. No expensive cleaners, no trays, no racks.
Lauren Bambusch is a microbiologist by trade as well as a writer and baker by hobby. She lives in Baltimore with her husband, three cats, a super-sized mutt, and a school of fish, all of whom root for her Alma mater, Michigan State. Go Green!