As a convenient and fast way to sterilize, the germicidal UVC lamp is one of the commonly used sterilization means in hospitals. However, there are certain problems in the use of traditional UVC sterilization equipment, such as large power consumption, low luminous efficiency, 1 ordinary UVC lamp power of more than 20 ~ 40 W. Germicidal UVC lamps rely mainly on the wavelength of 250 ~ 280 nm short-wave ultraviolet (UVC), in addition to sterilization, but also a certain risk to human health. With the rapid development of LED technology, light-emitting diodes as a light source become a powerful means of saving energy and extending the service life of lamps. Compared with ordinary UVC lamps, the LED UVC lamp uses UVC semiconductors with a more concentrated wavelength range of emission, which greatly improves the luminous efficiency and germicidal ability and reduces power consumption. In this study, LED UVC lamps with a wavelength of 275 ± 5 nm and output power of only 0.12 W were used for laboratory observations of the germicidal effect of LED UVC lamps and the factors affecting the germicidal effect.
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1 Material and Methods
1) Test material
The LED UV lamp used in the study was a Taiwanese product with a central wavelength of 275 nm and output power of 0.12 W. The radiation intensity was 2. 8 μW/cm² at a distance of 5 cm. the central wavelength is 275 nm, the output power is 0.12 W, and the radiation intensity is 2. 8 μW/cm² at an irradiation distance of 5 cm.
The test indicator bacteria were Staphylococcus aureus (ATCC 25922) and Escherichia coli (ATCC 25922) and E. coli (ATCC 25923), which were provided by the strain room of the Microbiology Department of Qingdao University School of Medicine. The culture and related equipment were provided by UVCA Group.
Other experimental instruments included precision electronic balance, an electric mixer, and automatic double-pure water distillation. the other instruments include precision electronic balance, electric mixer, automatic double pure water distiller, pressure steam sterilizer, electric constant temperature incubator, electric constant temperature blast dryer, etc.
2) Test method
① Preparation of bacterial suspension and bacterial vector
The typical colonies cultured on fresh medium plates were placed the inappropriate amount of sterilized saline, shaken and mixed, and the bacterial suspension containing 1.5 × 108 cfu/ml was prepared by the turbidimetric method, and then further diluted and prepared into the bacterial suspension containing 1.5 × 106 cfu/ml required for the experiment.the bacterial suspension was further diluted to 1.5 × 106 cfu/ml. Take 10 μl of the suspension and add it onto a sterilized filter paper sheet of 10 mm × 10 mm, and let it dry naturally at room temperature, and then use it as a carrier (bacterial sheet).
② Disinfection by irradiation
The stained side of the slices was placed in a sterile dish and irradiated under the LED UV lamp at different design distances as the test group; the slices not irradiated by the LED UV lamp were used as the positive control.
③ UVC lamp disinfection effect detection
The slices irradiated for different times were put into sterile tubes containing 5.0 ml of dilution solution (the same for the positive control slices), and then eluted by full shaking in an electric mixer, and the positive control was diluted appropriately. After the agar solidified, incubate in a constant temperature incubator at 37℃ for 24~48 h. Count the number of colonies and calculate the killing rate. The test was repeated three times.
3) Statistical analysis
SPSS 20.0 statistical software was used to process the above experimental results, and the bactericidal rate was analyzed by ANOVA after square root inverse sine transformation with the test level α = 0.05.
1) Effectiveness of killing Staphylococcus aureus
The test results showed that the killing rate of Staphylococcus aureus on the infected carriers was 100% when the LED UVC lamp was irradiated for 5 min at a vertical distance of 2 to 5 cm. The UV radiation intensity of the lamp decreased from 9.2 μW/cm² to 1.9 μW/cm² as the irradiation distance increased from 2 cm to 6 cm; however, the killing effect increased with increasing irradiation time at the same distance (Table 1).
Table 1 Germicidal effect of LED UVC lamp irradiation on Staphylococcus aureus
|Illumination distance(cm)||Radiation intensity ( μW/cm²)||Average kill rate at 1 min ( % )||Average kill rate at 2 min ( % )||Average kill rate at 3 min ( % )||Average kill rate at 4 min ( % )||Average kill rate at 5 min ( % )|
|2||9.2||91.37||97.21||100. 00||100. 00||100. 00|
|3||7.1||88.10||94. 00||97. 54||100. 00||100. 00|
|4||4.3||74. 68||82. 89||96.39||99.01||100. 00|
|5||2.8||38. 95||55.83||70.77||81.14||100. 00|
|6||1.9||26. 99||52. 40||79.88||85.48||97. 04|
Note: The number of positive controls was 16 200 cfu/tablet.
2) Effect of killing E. coli
The results showed that the kill rate of E. coli on the carrier was 100% with the LED UVC lamp irradiated at a vertical distance of 2 to 4 cm for more than 15 min. The bactericidal effect increased with increasing irradiation time at each irradiation distance (Table 2).
Table 2 Germicidal effect of LED UVC lamp irradiation on E. coli
|Illumination distance(cm)||Radiation intensity ( μW/cm²)||Average kill rate at 1 min ( % )||Average kill rate at 3 min ( % )||Average kill rate at 5 min ( % )||Average kill rate at 10 min ( % )||Average kill rate at 15 min ( % )|
|2||9.2||89.03||94. 08||99.55||100. 00||100. 00|
|4||4.3||73.20||87. 17||92.99||96.16||100. 00|
|5||2.8||59. 21||77.59||88.46||93. 78||99.83|
Note: The number of positive controls was 17 700 cfu/tablet.
Compared with ordinary UVC lamps, LED UVC lamps have a broad clinical application prospect because of their low power consumption, high luminous efficiency, long life, and small size.
In this test, the LED UVC lamp has a good sterilization effect on both S. aureus and E. coli. when the irradiation distance of the LED UVC lamp is certain, the sterilization rate increases gradually with the extension of irradiation time and decreases gradually with the increase of irradiation distance. When the irradiation distance is less than 5 cm, irradiation time is greater than 5 min, the sterilization rate of Staphylococcus aureus reached 100%; when the irradiation distance is less than 4 cm, irradiation time is greater than 15 min, the sterilization rate of Escherichia coli reached 100%. It is generally believed that the germicidal effect of UVC lamps is closely related to the irradiation intensity, time, and distance is closely related.
The results of this test show that the LED UVC lamp with the vertical irradiation distance increases, the intensity of UV radiation significantly reduced, so the UVC lamp with increasing irradiation distance, the germicidal effect significantly reduced, while in the same irradiation distance with the irradiation time to increase the germicidal effect. Therefore, the intensity of UV radiation is an important factor affecting the germicidal effect, irradiation time and irradiation distance will directly affect the germicidal effect of the UVC lamp.
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