Bumah Violet V, Masson-Meyers Daniela S, Cashin Susan, Enwemeka Chukuka S
College of Health Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, 53211.
Lasers Surg Med. 2015 Mar;47(3):266-72. doi: 10.1002/lsm.22327. Epub 2015 Jan 12.
In previous studies, we showed that irradiation with 405 nm or 470 nm light suppresses up to 92% methicillin-resistant Staphylococcus aureus (MRSA) growth in vitro and that the remaining bacteria re-colonize. In this study, the aim was to develop a protocol that yields 100% MRSA growth suppression.
We cultured 3 × 10(6) and 5 × 10(6) CFU/ml USA300 strain of MRSA and then irradiated each plate with varying fluences of 1-60 J/cm2 of 405 nm or 470 nm light, either once or twice at 6 hours intervals. Next, we plated 7 × 10(6) CFU/ml and irradiated it with 45, 50, 55, or 60 J/cm2 fluence, once, twice, or thrice at the same 6 hours intervals. In a third experiment, the same culture density was irradiated with 0, 165, 180, 220, or 240 J/cm(2) , either once, twice, or thrice.
Irradiation with either wavelength significantly reduced the bacterial colonies regardless of bacterial density (P < 0.05). At 3 × 10(6) CFU/ml density, nearly 40% and 50% growth of MRSA were suppressed with as little as 3 J/cm2 of 405 nm and 470 nm wavelengths, respectively. Moreover, 100% of the colonies were suppressed with a single exposure to 55 or 60 J/cm2 of 470 nm light or double treatment with 50, 55, or 60 J/cm2 of 405 nm wavelength. At 5 × 10(6) CFU/ml density, irradiating twice with 50, 55, or 60 J/cm2 of either wavelength suppressed bacterial growth completely, lower fluences did not. The denser 7 × 10(6) CFU/ml culture required higher doses to achieve 100% suppression, either one shot with 220 J/cm2 of 470 nm light or two shots of the same dose using 405 nm.
The bactericidal effect of blue light can be optimized to yield 100% bacterial growth suppression, but with relatively high fluences for dense bacterial cultures, such as 7 × 10(6) CFU/ml.
在之前的研究中，我们发现用405纳米或470纳米光照射可在体外抑制高达92%的耐甲氧西林金黄色葡萄球菌（MRSA）生长，且剩余细菌会重新定植。在本研究中，目标是制定一种能实现100%抑制MRSA生长的方案。
我们培养了每毫升3×10⁶和5×10⁶ 菌落形成单位（CFU）的USA300株MRSA，然后用1 - 60焦每平方厘米的不同能量密度的405纳米或470纳米光照射每个培养皿，照射一次或每隔6小时照射两次。接下来，我们接种每毫升7×10⁶ CFU并分别用45、50、55或60焦每平方厘米的能量密度照射，同样每隔6小时照射一次、两次或三次。在第三个实验中，用0、165、180、220或240焦每平方厘米照射相同培养密度的菌液，照射一次、两次或三次。
无论细菌密度如何，用这两种波长的光照射均能显著减少细菌菌落数量（P < 0.05）。在每毫升3×10⁶ CFU的密度下，仅用3焦每平方厘米的405纳米和470纳米波长的光分别可抑制近40%和50%的MRSA生长。此外，单次暴露于55或60焦每平方厘米的470纳米光或用50、55或60焦每平方厘米的405纳米波长光进行两次处理可100%抑制菌落生长。在每毫升5×10⁶ CFU的密度下，用50、55或60焦每平方厘米的任一波长光照射两次可完全抑制细菌生长，较低能量密度则不能。密度更高的每毫升7×10⁶ CFU的培养物需要更高剂量才能实现100%抑制，即单次用220焦每平方厘米的470纳米光照射或用405纳米光分两次照射相同剂量。
蓝光的杀菌效果可优化以实现100%抑制细菌生长，但对于高密度细菌培养物，如每毫升7×10⁶ CFU，需要相对较高的能量密度。
