Proof-of-Concept of Sterilization with a Six Nines Kill Rate (Kill Rate = 99.9999%) versus Disinfection with a Three Nines Kill Rate (Kill Rate = 99.9%) Using Ultra-Violet Irradiation at 260-280 nm Wavelengths (UV-C) Via Low Cost, Low Energy Consumption, Light Emitting Diodes*

Antibiotic resistant bacteria [1], the 2019 SARS-CoV-2 pandemic [2], and new infectious agents [2] require rapid, safe and reliable eradication of pathogens. 

FDA/CDC accepted sterilization methods are autoclaving, γ-ray Irradiation, and exposure to ethylene oxide gas at 65 C. All are expensive, time-consuming, and hazardous. The FDA criteria for sterilization is a Sterility Assurance Level (SAL) of 10^-6, the probability of a single viable micro-organism occurring on an item after sterilization. 10^-6 corresponds to eradication of 10⁶ Colony Forming Units (CFUs) or a kill rate of 99.9999% [2].

Our work investigates cheaper, safer, and faster sterilization via UV-C irradiation at 260-280 nm. UV-C breaks amino acid bonds in RNA/DNA, inhibits growth and eradicates pathogen. UV-C has many advantages, including destroying a broad range of pathogens in air without heat.

Kowalski [3-6] and Rheed [7] have shown that UV-C achieves a SAL = 10^-3 and can be widely used in water sanitation. However, full sterilization by UV-C to a SAL = 10^-6 hasn't been established.

Can 10⁶ CFUs be reproducibly eradicated via UV-C? Can low cost, low energy consumption UVC LED irradiation reliably achieve sterilization at 260-280 nm? Our previous work shows that UV-C LEDs are effective and more reliable than high energy consumption Fluorescent UV tubes [8]. The present study uses 2 parallel sets of calibrated bacterial cultures of 20 million LactoB. A. CFUs and demonstrates a kill rate of six nines (99.9999%) using 6 sets of ten serial dilutions.