405-nm light for bacterial reduction in blood plasma: the impact of varying the method of dose delivery on antimicrobial efficacy and blood product quality

Background: The introduction of risk control measures, other than in situ pathogen inactivation, have reduced the risk of transfusion-transmitted viral infections to an acceptable level. However, newly emerging and re-emerging pathogens including bacterial contamination of transfusion blood products remain a major concern to blood safety. Antibacterial violet-blue light, in the region of 405 nm, is demonstrating early potential as a bacterial reduction tool for human blood plasma and platelet concentrates, without the need for external photosensitizers. Previous studies have established light doses that provide antibacterial efficacy for decontamination of blood platelets and plasma; however, it is important to understand how delivery of this light dose (high irradiance light over short treatment times versus lower light irradiances over longer treatment periods) may impact antibacterial efficacy and/or blood product quality.

Aims: This study investigates the effects of exposing human blood plasma to fixed doses of 405 nm light, with the dose applied using different treatment regimens, and assesses the effects on antibacterial efficacy and blood plasma protein integrity.

Methods: Human blood plasma (unseeded and seeded with ~105 CFUmL−1 Staphylococcus aureus) was exposed to 405 nm light at irradiances of 1, 10 and 100 mWcm−2, for up to 100, 10 and 1-hr treatment times, respectively. These different treatment regimens provided applied doses of up to 360 Jcm−2. The antibacterial efficacy and compatibility of the different dose regimens were assessed using bacterial inactivation assays and preliminary protein stability tests using SDS-PAGE.

Results: All 405 nm light treatment regimens significantly reduced the bacterial load in human blood plasma (98.9–100% reduction by 360 Jcm−2; P < 0.05). Use of low irradiance (1 mWcm−2) light was more efficient for bacterial inactivation, compared to the higher irradiances of 10 and 100 mWcm−2, with 99.66% reduction achieved with 144 Jcm−2. However, use of 100 mWcm−2 irradiance achieved significant bacterial reductions in the shortest exposure time (12 minutes; P = 0.001).

The electrophoretic pattern of plasma exposed to 405 nm light doses ≤ 180 Jcm−2 did not evidence visually detectable differences between dose delivery methods. The first evidence of protein modification was observed in the electrophoretic pattern of plasma exposed to a dose of 252 Jcm−2 delivered by a low irradiance (1 mWcm−2 for 70-hr exposure). However, no major protein damage was visually detected after plasma was exposed to an effective antibacterial dose of 360 Jcm−2 delivered using 1, 10 or 100 mWcm−2 irradiances.

Summary/Conclusions: This study demonstrates that varying the method of dose delivery regimen can significantly affect the germicidal efficiency of 405 nm light for the treatment of blood plasma. In particular, the use of a low irradiance over an extended exposure period was determined to the most efficient germicidal method of dose delivery. Preliminary protein stability tests however indicate that the method of dose delivery has a minimal effect on blood plasma quality. Key findings from this study will advance the understanding of the biological interactions of 405 nm antimicrobial light with blood plasma, and aid in optimising its development as a pathogen reduction tool for human blood plasma.