Effect of therapeutic UVC on corneal DNA: Safety assessment for potential keratitis treatment

Novel treatment of infectious keratitis in canine corneas using ultraviolet C (UV-C) light

OBJECTIVE

To investigate the therapeutic effect of 275 nm wavelength ultraviolet C (UV-C) light for treatment of bacterial keratitis in canine corneas using an affordable, broadly available modified handheld device.

METHODS

UV-C therapy (UVCT) was evaluated in two experiments: in vitro using triplicates of three bacterial genera (Staphylococcus, Streptococcus, Pseudomonas spp., and a mix of all species) where the UVCT was performed at a distance of 10, 15, and 20 mm with 1 or 2 doses (4 h apart) for 5, 15, or 30 s; ex vivo model where healthy canine corneal buttons were inoculated superficially and deep (330 μm) with the same bacterial isolates and treated at a 10 mm distance for 15 s with one dose of 22.5 mJ/cm2. Fluorescent marker (STYO9-PI) was used to label (green = live bacteria, red = dead bacteria), and confocal microscopy was used to image the bacteria.

RESULTS

In vitro results showed all plates treated with UVCT had 100% bactericidal effect for all isolates with single dose of 15 s at 10 mm distance or two doses, 4 h apart at 15 mm and was ineffective with single dose at 15-20 mm. The ex vivo results confirmed a significant decrease in bacterial load for all isolates on samples inoculated superficially but were inconclusive for intrastromal ones.

CONCLUSIONS

UVCT confirmed the therapeutic potential for all tested isolates, for both in vitro and ex vivo experiments using a single exposure of 15 s. While safety studies are underway, clinical trials are warranted.

Antimicrobial Resistance: Is There a 'Light' at the End of the Tunnel?

In recent years, with the increases in microorganisms that express a multitude of antimicrobial resistance (AMR) mechanisms, the threat of antimicrobial resistance in the global population has reached critical levels. The introduction of the COVID-19 pandemic has further contributed to the influx of infections caused by multidrug-resistant organisms (MDROs), which has placed significant pressure on healthcare systems. For over a century, the potential for light-based approaches targeted at combatting both cancer and infectious diseases has been proposed. They offer effective killing of microbial pathogens, regardless of AMR status, and have not typically been associated with high propensities of resistance development. To that end, the goal of this review is to describe the different mechanisms that drive AMR, including intrinsic, phenotypic, and acquired resistance mechanisms. Additionally, the different light-based approaches, including antimicrobial photodynamic therapy (aPDT), antimicrobial blue light (aBL), and ultraviolet (UV) light, will be discussed as potential alternatives or adjunct therapies with conventional antimicrobials. Lastly, we will evaluate the feasibility and requirements associated with integration of light-based approaches into the clinical pipeline.

Managing Corneal Infections: Out with the old, in with the new?

There have been multiple reports of eye infections caused by antibiotic-resistant bacteria, with increasing evidence of ineffective treatment outcomes from existing therapies. With respect to corneal infections, the most commonly used antibiotics (fluoroquinolones, aminoglycosides, and cephalosporines) are demonstrating reduced efficacy against bacterial keratitis isolates. While traditional methods are losing efficacy, several novel technologies are under investigation, including light-based anti-infective technology with or without chemical substrates, phage therapy, and probiotics. Many of these methods show non-selective antimicrobial activity with potential development as broad-spectrum antimicrobial agents. Multiple preclinical studies and a limited number of clinical case studies have confirmed the efficacy of some of these novel methods. However, given the rapid evolution of corneal infections, their treatment requires rapid institution to limit the impact on vision and prevent complications such as scarring and corneal perforation. Given their rapid effects on microbial viability, light-based technologies seem particularly promising in this regard.

UV C Light from a Light-Emitting Diode at 275 Nanometers Shortens Wound Healing Time in Bacterium- and Fungus-Infected Skin in Mice

Due to the changes in pathogenic species and the absence of research on topical skin antibiotics, the therapy of skin and soft tissue infections (SSTIs) is facing more and more severe challenges. It is particularly urgent to look for alternative therapies without induction of drug resistance. UV C (UVC) light within the range of 200 to 280 nm is one of the most common techniques used to kill and/or inactivate pathogenic microorganisms. However, the traditional most commonly used wavelength of 254 nm irradiated from a low-pressure mercury lamp is hazardous to human health, being both carcinogenic and damaging to eye tissues, which limits its applications in vivo. This research aimed to investigate the antimicrobial properties and influence of 275-nm UVC light from a light-emitting diode (UVC-LED light) on wound healing time. Five bacteria, three fungi, and scalded-mouse models combined with SSTIs were used to evaluate the antimicrobial effect in vitro and in vivo. 275-nm UVC-LED light inactivated both bacteria and fungi with a very short irradiation time in vitro and induced neither DNA damage nor epidermal lesions in the mice's skin. Furthermore, in mouse models of SSTIs induced by either methicillin-resistant Staphylococcus aureus (MRSA) or Candida albicans, the 275-nm UVC-LED light showed significant antimicrobial effects and shortened the wound healing time compared with that in the no-irradiation group. UVC-LED light at 275 nm has the potential to be a new form of physical therapy for SSTIs. IMPORTANCE As a common clinical problem, the therapy of SSTIs is facing growing challenges due to an increase in the number of drug-resistant bacteria and fungi. UV C (UVC) light sterilization has been widely used in all aspects of daily life, but there are very few reports about in vivo therapy using UVC light. It is well known that prolonged exposure to UVC light increases the possibility of skin cancer. In addition, it is also very harmful for eyes. UV irradiation with 254-nm UVC light can cause corneal damage, like thinning of the corneal epithelial layer, superficial punctate keratitis, corneal erosion, etc. In this study, we focused on looking for a more accessible light source and safer UVC wavelength, and 275-nm UVC LED light was chosen. We investigated its applicability for SSTIs therapy with relative skin safety and expected that it could be used as a new physical therapy method for SSTIs.

Preclinical confirmation of UVC efficacy in treating infectious keratitis

PURPOSE

Preclinical evaluation of the therapeutic potential of antimicrobial 265 nm UVC for infectious keratitis.

METHODS

Four experiments explored UVC: 1) impact on bacterial and fungal lawns on agar, in individual or mixed culture, 2) bacterial inactivation dose in an in vitro deep corneal infection model, 3) dose validation in an ex vivo porcine keratitis model and 4) efficacy in a masked, randomised, controlled murine keratitis trial using bioluminescent Pseudomonas aeruginosa.

RESULTS

Minimum effective UVC exposures ranged between 2 s and 5 s for lawn bacteria and fungi in individual or mixed culture. Significant P. aeruginosa growth inhibition in the in vitro infection model was achieved with 15 s UVC, that resulted in a >3.5 log10 reduction of bacteria in a subsequent ex vivo keratitis model (p < 0.05). Bioluminescence fell below baseline levels in all treated animals, within 8 h of treatment (p < 0.05), in the in vivo study. Re-epithelialisation with corneal clarity occurred within 24 h in 75% of UVC-treated cases, with no relapse at 48 h. On plating, bacteria were recovered only from untreated controls.

CONCLUSIONS

UVC inhibited all tested bacteria and fungi, including mixed culture and strains linked to antibiotic resistance, in vitro, with exposures of ≤ 5 s. In vitro and ex vivo testing confirmed therapeutic potential of 15 s UVC. In vivo, 15 s UVC administered in two doses, 4 h apart, proved effective in treating murine bacterial keratitis.

Risk Factors, Clinical Outcomes, and Prognostic Factors of Bacterial Keratitis: The Nottingham Infectious Keratitis Study

Background/Aim: To examine the risk factors, clinical characteristics, outcomes, and prognostic factors of bacterial keratitis (BK) in Nottingham, UK.

Methods: This was a retrospective study of patients who presented to the Queen's Medical Centre, Nottingham, with suspected BK during 2015–2019. Relevant data, including the demographic factors, risk factors, clinical outcomes, and potential prognostic factors, were analysed.

Results: A total of 283 patients (n = 283 eyes) were included; mean age was 54.4 ± 21.0 years and 50.9% were male. Of 283 cases, 128 (45.2%) cases were culture-positive. Relevant risk factors were identified in 96.5% patients, with ocular surface diseases (47.3%), contact lens wear (35.3%) and systemic immunosuppression (18.4%) being the most common factors. Contact lens wear was most commonly associated with P. aeruginosa whereas Staphylococci spp. were most commonly implicated in non-contact lens-related BK cases (p = 0.017). At presentation, culture-positive cases were associated with older age, worse presenting corrected-distance-visual-acuity (CDVA), use of topical corticosteroids, larger epithelial defect and infiltrate, central location and hypopyon (all p < 0.01), when compared to culture-negative cases. Hospitalisation was required in 57.2% patients, with a mean length of stay of 8.0 ± 8.3 days. Surgical intervention was required in 16.3% patients. Significant complications such as threatened/actual corneal perforation (8.8%), loss of perception of light vision (3.9%), and evisceration/enucleation (1.4%) were noted. Poor visual outcome (final corrected-distance-visual-acuity of <0.6 logMAR) and delayed corneal healing (>30 days from initial presentation) were significantly affected by age >50 years, infiltrate size >3 mm, and reduced presenting vision (all p < 0.05).

Conclusion: BK represents a significant ocular morbidity in the UK, with ocular surface diseases, contact lens wear, and systemic immunosuppression being the main risk factors. Older age, large infiltrate, and poor presenting vision were predictive of poor visual outcome and delayed corneal healing, highlighting the importance of prevention and early intervention for BK.

Can microorganisms develop resistance against light based anti-infective agents?

Recently, there have been increasing numbers of publications illustrating the potential of light-based antimicrobial therapies to combat antimicrobial resistance. Several modalities, in particular, which have proven antimicrobial efficacy against a wide range of pathogenic microbes include: photodynamic therapy (PDT), ultraviolet light (UVA, UVB and UVC), and antimicrobial blue light (aBL). Using these techniques, microbial cells can be inactivated rapidly, either by inducing reactive oxygen species that are deleterious to the microbial cells (PDT, aBL and UVA) or by causing irreversible DNA damage via direct absorption (UVB and UVC). Given the multi-targeted nature of light-based antimicrobial modalities, it has been hypothesised that resistance development to these approaches is highly unlikely. Furthermore, with the exception of a small number of studies, it has been found that resistance to light based anti-infective agents appears unlikely, irrespective of the modality in question. The concurrent literature however stipulates, that further studies should incorporate standardised microbial tolerance assessments for light-based therapies to better assess the reproducibility of these observations.

Safety and efficacy of UV application for superficial infections in humans: A systematic review and meta-analysis

BACKGROUND

Ultraviolet (UV) light is naturally antimicrobial, but risks associated with UV overexposure have limited its clinical application. This systematic review evaluates the safety and efficacy of UV light treatment of superficial human infections.

METHODS

MEDLINE, Embase, Cochrane CENTRAL, ANZCTR and US National Library of Medicine were searched (March 25, 2020). Clinical studies applying UV light (200-400 nm) for superficial infections and non-clinical studies evaluating the antimicrobial effects of UV light on human samples were included. Randomised controlled trials (RCTs) and non- RCTs were appraised using the Cochrane risk of bias and the ROBINS-I tools, respectively.

RESULTS

Eleven RCTs, seven non-RCTs, 24 case studies, and 11 in vitro studies were included. Most clinical studies (34/42) evaluated UVA treatment for microbial keratitis (MK) using cross-linking (UVA-CXL) methods. Six clinical studies assessed UVC; one, UVB; and one, broadband UV for chronic skin infections. Pooled data analysis showed no difference in the time to wound resolution with UVA-CXL relative to standard treatment (mean difference [MD]: -18.20 [95% CI: -39.04 to 2.65] days; p = 0.09). Adverse event incidence was similar to control for UVA-CXL in MK (RR: 0.70 [95%CI: 0.32-1.79]; 5 RCTs) and UVC in skin infections (RR: 0.63 [95%CI: 0.25-1.54]; 2 RCTs).

CONCLUSION

Alone or as an adjunct to standard therapy, UV light shows promise as a safe and effective treatment for a wide range of infections. Applications of UV light as an anti-infective agent are deserving of further evaluation, especially in the context of growing antibiotic resistance.

REGISTRATION

PROSPERO registration number CRD42020176510.