Fig 1.
Experimental setup for MRSA area disinfection assay and survival assay.
The experimental setup for the MRSA survival assay includes a far-UVC laser module, a fiber optic cable connecting the laser to an optical diffuser, and an agar filled petri dish. The diffuser was suspended in air 1 cm above the surface of the agar in the dish. For the cell survival assay the diffuser was aligned on top of four identical 5-μl aliquots of 106 CFU/ml of MRSA, each with an area of about 5 mm in diameter. An identical equipment setup was used for the area disinfection assay except 50 μl of MRSA was spread to cover the entire surface of the dish.
Fig 2.
Area of MRSA sterilization after diffused far-UVC exposure.
A picture of the MRSA growth pattern after exposure to diffused far-UVC light shows the ability to sterilize a large area using a single laser source. The MRSA appears as darker regions against the lighter colored agar. A contour map of the exposure dose, calculated using film exposures with the same experimental setup and expressed in mJ/cm2, is overlaid to show that variations in dose have a clear correlation with the killing efficiency. A picture of the dish without doses overlaid is shown in the top right.
Fig 3.
MRSA survival fraction for far-UVC exposure doses.
Results for the survival assay for the killing of MRSA on a surface using far-UVC light emitted from a diffuser are plotted as bacterial survival fraction relative to zero-dose controls for the different exposures. The means and standard errors refer to triplicate repeat studies and the line represents the best-fit regression to Eq 1. The data follow a log-linear decay with a rate constant of 0.51 cm2/mJ. The calculated exposure dose required to kill 90% of bacteria is D90 = 4.5 mJ/cm2.
Table 1.
Raw bacteria count data obtained from the survival assay experiments.