Efficacy of Violet-Blue (405 nm) LED Lamps for Disinfection of High-Environmental-Contact Surfaces in Healthcare Facilities: Leading to the Inactivation of Microorganisms and Reduction of MRSA Contamination

Effective disinfection procedures in healthcare facilities are essential to prevent transmission. Chemical disinfectants, hydrogen peroxide vapour (HPV) systems and ultraviolet (UV) light are commonly used methods. An emerging method, violet-blue light at 405 nm, has shown promise for surface disinfection. Its antimicrobial properties are based on producing reactive oxygen species (ROS) that lead to the inactivation of pathogens. Studies have shown significant efficacy in reducing bacterial levels on surfaces and in the air, reducing nosocomial infections. The aim of this study was to evaluate the antimicrobial effectiveness of violet-blue (405 nm) LED lamps on high-contact surfaces in a hospital infection-control laboratory. High-contact surfaces were sampled before and after 7 days of exposure to violet-blue light. In addition, the effect of violet-blue light on MRSA-contaminated surfaces was investigated. Exposure to violet-blue light significantly reduced the number of bacteria, yeasts and moulds on the sampled surfaces. The incubator handle showed a low microbial load and no growth after irradiation. The worktable and sink showed an inconsistent reduction due to shaded areas. In the second experiment, violet-blue light significantly reduced the microbial load of MRSA on surfaces, with a greater reduction on steel surfaces than on plastic surfaces. Violet-blue light at 405 nm has proven to be an effective tool for pathogen inactivation in healthcare settings Violet-blue light shows promise as an additional and integrated tool to reduce microbial contamination in hospital environments but must be used in combination with standard cleaning practices and infection control protocols. Further research is needed to optimise the violet-blue, 405 nm disinfection method.

Wind of change: Better air for microbial environmental control

Background

The COVID19 epidemic highlighted the importance of air in the transmission of pathogens. Air disinfection is one of the key points to reduce the risk of transmission both in the health sector and in public, civil and industrial environments. All bacteria and viruses tested to date can be inactivated by UV-C rays. Laboratory tested UV-C systems are increasingly popular and proposed as effective technologies for air purification; few studies have evaluated their performance in populated indoor environments. The aim of this investigation was to evaluate the effectiveness of a UV-C disinfection system for air in a real working context.

Methods

This experimental study was conducted between December 2020 and February 2021 in an office of the Department of Molecular and Developmental Medicine of the University of Siena, Italy. A pre-final version air purifier (Cleaning Air T12), capable of treating 210 m³/h of air, was first tested for its ability to filter particulates and reduce microbial air contamination in the absence of people. Subsequently, the experiments were conducted in the presence of 3-5 subjects who worked for several hours in an office. During the tests, microbiological samples of air were collected in real time, switching the system on and off periodically. Air samples were collected and incubated on Petri dishes at 36 °C and 22 °C. Statistical analysis was performed with Stata 16 software assuming a significance level of 95%. An interpolating model was identified to describe the dynamics of contamination reduction when the device operates.

Results

Preliminary tests showed a significant 62.5% reduction in Colony-Forming Units (CFUs) with 36 °C incubation. Reductions in the particulate component were also observed. In the main test, comparison of CFU data, between the device-on phase (90 min) and the subsequent device-off phase (60 min), showed statistically significant increase (p = 0.001) of environmental contamination passing from a mean of 86.6 (65.8-107.4) to 171.1 (143.9-198.3) CFU/m³, that is a rise of about 100%. The interpolating model exhibited a good fit of CFU reduction trend with the device on.

Conclusions

The system, which mainly uses UV-C lamps for disinfection, was able to significantly reduce environmental and human contamination in real time. Experimental tests have shown that as soon as the device is switched off, after at least half an hour of operation, the healthiness of the air decreases drastically within 10 minutes, bringing the airborne microbial contamination (induced by the presence of operators in the environment) to levels even higher than 150% of the last value with the device on. Re-engineering strategies for system improvement were also discussed.

Efficacy of violet-blue light to inactive microbial growth

The increase in health care-associated infections and antibiotic resistance has led to a growing interest in the search for innovative technologies to solve these problems. In recent years, the interest of the scientific community has focused on violet-blue light at 405 nm (VBL405). This study aimed to assess the VBL405 efficiency in reducing microbial growth on surfaces and air. This descriptive study run between July and October 2020. Petri dishes were contaminated with P. aeruginosa, E. coli, S. aureus, S. typhimurium, K. pneumoniae and were placed at 2 and 3 m from a LED light source having a wavelength peak at 405 nm and an irradiance respectively of 967 and 497 µW/cm². Simultaneously, the air in the room was sampled for 5 days with two air samplers (SAS) before and after the exposition to the VBL405 source. The highest microbial reduction was reached 2 m directly under the light source: S. typhimurium (2.93 log₁₀), K. pneumoniae (2.30 log₁₀), S. aureus (3.98 log₁₀), E. coli (3.83 log₁₀), P. aeruginosa (3.86 log₁₀). At a distance of 3 m from the light source, the greatest reduction was observed for S. aureus (3.49 log₁₀), and P. aeruginosa (3.80 log₁₀). An average percent microbial reduction of about 70% was found in the sampled air after 12 h of exposure to VBL405. VBL405 has proven to contrast microbial growth on the plates. Implementing this technology in the environment to provide continuous disinfection and to control microbial presence, even in the presence of people, may be an innovative solution.

Wind of change: better air for microbial environmental control

Background

COVID19 outbreak highlighted air disinfection's importance. All bacteria and viruses tested to date (including various coronaviruses) respond to UV-C disinfection. This study aims to assess the effectiveness of an UVC disinfection system for air in a real working context.

Methods

This descriptive study was carried out in November 2020 in an office of the Department of Molecular and Developmental Medicine at the University of Siena. The disinfecting air system, Cleaning Air T12, produced by Italia Iso Group, has 12 lamps of 6.9 Watt of UVC/each, two inlet grills in its bottom and 2 outlet grills in the superior part. The volume of air that the system treat is of 210m3/h. The experiments were run over several days during the activities of 3-5 subjects working for several hours. Real time microbial air samplings were run during the tests switching the system ON and OFF. To verify microbial time variation, initial samplings (phase 1) had the system OFF, then ON (phase 2) and finally OFF again (phase 3). Petri dishes were incubated at 36 and 22 C°. Statistical analysis was executed with Stata 16. Significance level was set at p < 0.05.

Results

The longest test highlighted that during phase 2, after 8 minutes from the end of phase 1, the system acted significantly (p = 0.001) on the reduction of environmental contamination up to a mean of 70 (95% C.I. 64 - 77) CFU/500 liters (about 70% at 22 °C) and 50% at 36 °C. In phase 3 the mean values became 171 (144 - 198) CFU/500 liters at 22C° and 259 (228-291) at 36 °C.

Conclusions

The system was able to significantly reduce the environmental contamination in real time. The experimental tests show how, as soon as the device is turned OFF after at least half an hour of operation, air healthiness drops dramatically within 10 minutes, bringing the levels of microbial contamination (induced by the presence of the operators in the room) to levels even higher than 150%.

Key messages

In order to convey a correct and truthful message about the disinfection capabilities of an air purification system, testing the device under real operating would be necessary. Testing the device under real operating conditions, with and without the presence of people in controlled environments, would be necessary before the final product is placed on the market.

Abstract PD03-01: EFFECT OF METFORMIN ON APOPTOSIS IN A PRESURGICAL TRIAL IN NON-DIABETIC PATIENTS WITH BREAST CANCER

BACKGROUND: metformin has been associated with antitumor activity in epidemiological and clinical studies. This effect has been related to different mechanisms of actions, including a reduction of the proliferative activity and an increase of apoptosis. We have recently shown that a 4 week pre-surgical treatment with metformin did not affect Ki-67 LI overall but reduced tumor proliferation Ki67 LI in breast cancer (BC) patients with insulin resistance (IR) (HOMA, fasting blood glucose (mmol/L)*insulin (mU/L)/22.5>2.8) or BMI>27 (Bonanni et al. JCO epub May 7, 2012). The objective of the current analysis was to determine whether metformin induced a modulation of apoptosis (TUNEL) overall and by HOMA index.

TRIAL DESIGN: After tumor biopsy we randomly allocated 200 non-diabetic women with operable breast cancer to either metformin (850 mg/bid) or placebo for 4 weeks prior to surgery. The primary outcome measure was the difference between arms in Ki-67 after 4 weeks of treatment. Here we analyzed the apoptotic cell nuclei in 88 consecutive core biopsies and their paired surgical samples from the initial 100 randomized subjects.

RESULTS: Median TUNEL levels at surgery (Metformin = 10%, IQR, 4–20, Placebo = 8%, IQR, 3–15) were significantly higher as compared with baseline (Metformin = 4%, IQR, 2–7, Placebo = 3%, IQR, 2–6, p < 0.0001), but no difference between arms was noted (p = 0.2, adjusted for age, BMI, TUNEL and Ki67 at baseline). Interestingly, Ki67 and TUNEL levels were highly and positively correlated both at baseline and at surgery (Spearman r=0.51, p < 0.0001). Furthermore, we found a trend to a different metformin effect by the HOMA index (p = 0.1). In the 59 women with HOMA <2.8 there was a higher level of TUNEL at surgery on metformin versus placebo (p = 0.05), while an opposite trend was found in the 28 women with HOMA>2.8 (p = 0.6).

CONCLUSIONS: The levels of TUNEL are significantly higher in the surgical specimens compared with baseline biopsy and are directly correlated with those of Ki-67 (TUNEL is high when Ki-67 is high). We found no significant modulation of TUNEL by metformin but a trend to a different effect according to the IR state, with a similar pattern to Ki-67: decrease by metformin in IR women and increase in non-IR women. Our findings confirm the notion that metformin has dual effects on breast cancer according to IR state. As expected, cancer apoptosis and proliferation are directly related. Our results strengthen the importance of placebo control arms in biomarker trials.

ACKNOWLEDGEMENTS: 2 Grants by AIRC and Italian Ministry of Health.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD03-01.