Syngergistic Efficacy of 405 nm Light and Hospital Disinfectants for the
Enhanced Decontamination of C. difficile on Clinically Relevant Surfaces
Sian Moorhead1, Michelle Maclean1, John E Coia2, Scott J MacGregor1, John G Anderson1
1 –The Robertson Trust Laboratory for Electronic Sterilisation Technologies (ROLEST), University of Strathclyde, Glasgow
2 – NHS Greater Glasgow & Clyde, Glasgow Royal Infirmary, Glasgow
Clostridium difficile
405 nm light
• Clostridium difficile spores are highly infectious and
resilient, and can survive in the environment for
prolonged periods.
• Rooms of patients with CDI can reach contamination
rates of up to 50%.
Bacterial count (log10 cfu/ml)
• Despite the development of a range of novel
disinfection and sterilisation technologies, C. difficile
remains a significant healthcare problem.
Bacterial count (log10 cfu/ml)
405nm light is a novel decontamination method
which inactivates bacteria by oxidative damage,
caused by photoexcitation of porphyrin molecules
within microbial cells.
•
Previous clinical studies have demonstrated the
effectiveness of this technology for environmental
decontamination (Maclean et al., 2014).
•
•
To investigate the synergistic effect of 405nm light
and the commonly used hospital disinfectants
sodium hypochlorite (NaOCl), Actichlor and Tristel
for the inactivation of C. difficile spores in
suspension and on surfaces.
•
Both 405nm light and the selected disinfectants
cause lethal oxidative damage to microorganisms,
therefore their combined use has the potential to
deliver enhanced sporicidal effects.
Efficacy against C. difficile spores has not yet been
fully established.
Methods
4
3
•
C. difficile spores were suspended in disinfectants, at
concentrations that had negligible effect on spores alone, and
exposed to 405 nm light (225 mW/cm2) (Fig. 1).
•
For surface exposures, spores were seeded onto the surface, and
incubated at 50°C for 25 min to allow drying. 50µl disinfectant
was then added to the surface, and this was then light exposed.
2
1
0
0
810
1620
2430
3240
1a
Dose (J/cm2)
Tristel alone
405nm light alone
Tristel and 405nmm light
5
4
3
2
0
810
1620
2430
Dose (J/cm2)
•
Surviving spores were enumerated by direct plate counts
(suspensions) and recovery by swabbing (surfaces).
•
Experiments were repeated in triplicate, with a minimum of
duplicate samples for each repeated exposure (n=>6).
•
To establish the sporicidal activity of each agent alone, control
samples were exposed to:
(i) 405 nm light in the absence of disinfectants, and
(ii) disinfectants in the absence of 405 nm light
3a
• The inactivation of spores simultaneously exposed to 405nm
light and disinfectants would then demonstrate the synergistic
activity of the combined sporicidal agents.
1
0
Bacterial count (log10 cfu/ml)
•
Methods and Results
NaOCl alone
405nm light alone
NaOCl and 405nm light
5
Aims
1b
3b
Actichlor alone
405nm light alone
Actichlor and 405nm light
5
4
3
2
1
0
0
810
1620
Dose (J/cm2)
2430
2
1c
Fig 1. Exposure of C. difficile spores to a range of
disinfectants in suspension ((a) 0.1% NaOCl, (b) 0.001%
Actichlor, (c) 0.0001% Tristel) in combination with 405
nm light at an irradiance of 225mW/cm2 .
Fig 2. Exposure of C. difficile spores seeded onto vinyl
flooring to 0.00001% Tristel in combination with 405
nm light at an irradiance of 225mW/cm2 .
3c
Fig 3. Exposure of C. difficile spores seeded onto
glass to (a) 0.01% NaOCl (b) 0.0001% Tristel and (c)
0.0001% Actichlor in combination with 405 nm light
at an irradiance of 225mW/cm2 .
Conclusions and Further Research Questions
•
In conclusion, it is evident that 405nm light alone can successfully be used for the inactivation of Clostridium difficile, however high light doses are required.
•
This work has demonstrated that a synergistic effect can be achieved with the combined use of 405nm light with disinfectants to enhance the sporicidal activity of
405nm light. Within the clinical environment this would enable the use of lower concentrations of chlorinated disinfectants which are potentially harmful to both users
and materials.
•
Spores on vinyl appear to be particularly susceptibility to the combined action of 405nm light and disinfectants. Further clinically-relevant surfaces, such as PVC,
stainless steel and aluminium, will be investigated in the future.
•
Future work will progress to investigate whether this synergistic sporicidal effect can be achieved with the use of lower irradiance 405nm light levels, similar to those
successfully utilised for environmental decontamination applications in the clinical environment.
Reference: Maclean, et al (2014). 405 nm light technology for the inactivation of pathogens and its potential role for environmental disinfection and infection control. J Hosp Infect, 88(1); 1-11.
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