UV Sterilizer Efficiency Test

The global COVID-19 pandemic has dramatically increased the demand for disinfection products. Of these, one of the most popular sterilizers that consumers have turned to are UV sterilizers. The principle of UV sterilization lies in the ultraviolet light that lend its name to these types of devices. Ultraviolet light carries a lot of energy, and this high-energy light—typically around 260 nm—can destroy the genetic material in a variety of pathogens, including fungi, bacteria, and viruses. Pathogens are unable to reproduce and function when their genetic material is damaged, and this in turn prevents them from causing harm to humans.

While the principle behind UV sterilization is relatively simple, there is an almost endless array of different UV sterilization product on the market, at a range of different price points. However, this diversity can be bewildering for the consumers and begs the question: do more expensive personal UV sterilize devices work better than those that cost less?

We investigated this question by assessing the sterilizing capabilities of two different UV sterilizers: “Lumin Sterilizer [1]” and “CP Lab Safety Mini UV Sterilizer [2]”. Lumin has a sleek design, programmable sterilization cycles, and uses a higher energy 13 W UV bulb. In contrast, CP Lab Mini Sterilizer has a more pared-down design and uses a 5 W UV bulb. Both UV bulbs operate at 254 nm, but the Lumin Sterilizer is 4-times more expensive than its more simply-designed competitor.

CP Lab Safety UV Sterilizer

Lumin Sterilizer

To put these two devices to the test, we prepared a liquid suspension of the common bacterial pathogen, Staphylococcus aureus. The bacteria was grown, prepared in a clear buffer solution, then a fixed volume of this bacteria suspension is dispensed into two different sterile plastic Petri dishes. One Petri dish is placed inside the Lumin Sterilizer, and the other is placed inside the CP Lab Safety Mini UV Sterilizer. Both devices ran for 5 minutes, as indicated by the manufacturer’s operating instruction. After the sterilization run, the Petri dishes were removed from each device, the bacteria suspension was serially diluted into buffer, and then 0.02 mL of each serial dilution was plated on agar plates labeled as “t_T” (time-test) to determine how many viable bacterial cells remain. To know how many bacteria were placed inside the UV sterilizers before sterilization took place, a portion of the bacteria buffer suspension that was not placed into the irradiated Petri dishes was also serially diluted and plated on separate agar plates, labeled as “t₀” (time-0).

After the agar plates were incubated, bacterial colonies grew on the respective t0 agar plates. The number of colonies were counted, and then we determined that the bacterial density that went into the UV sterilizers was approximately 50 million colonies per milliliter. However, no colonies were recovered on the respective t_T agar plates, indicating that after 5 minutes in the Lumin Sterilizer (agar plates labeled in red) or the CP Lab Safety Mini UV Sterilizer (agar plates labeled in blue), the bacterial density had fallen below the limit of the detection for the assay, which is 500 colonies per milliliter. This is a one million-fold reduction in the number of bacteria following irradiation. The result of this side-by-side comparison shows that the efficacy of two differently priced devices are comparable.

References: 

1. Purchased from Amazon
2. Purchased from CP Lab Safety

About the authors:

Gonzalo Martin was an intern at Emery Pharma from December through January 2019. Throughout his Capstone Mentorship, he was able to support projects related to Biology and Business Development activities. During his internship at Emery Pharma, he was senior and attended South San Francisco High School. He is currently attending San Francisco State University and studying environmental sciences.

Dr. Janet Liu is currently the Director of Microbiology and is responsible for R&D and cGMP/GLP projects involving antimicrobial susceptibility testing, antimicrobial synergy, biofilm testing, time-kill assays, and cytotoxicity testing. Dr. Liu received her Ph.D. in Biomedical Sciences from the University of California, Irvine. She received her B.S. in Biological Sciences from the University of California, Davis.