Experimental Study On Blue Light Killing Methicillin-resistant Staphylococcus Aureus(MRSA)

Background and objectiveMethicillin-resistant Staphylococcus aureus (MRSA) infection is an importantcause of impaired wound healing in trauma patients, and even leading to severemortality; what’s more, its high antibiotic resistance is a significant challenge inanti-MRSA therapy. The most important factor resulting MRSA infection is the abuseof antibiotics. Currently, clinical guidelines recommend symptomatic antibiotics,appropriate dose and early treatment for anti-MRSA. As we know, it is necessary ofusing antibiotics drug for anti-MRSA, but it will be easy to cause a greater degree ofresistance to MRSA. In some countries, the emergence of MRSA resistant toVancomycin and even all antibiotics has been reported. In1970s, Costerton putforward a concept of bacterial biofilm (BF) and noted that most bacteria widelydistributed in nature are surviving in biofilm state. Bacterial biofilm is an importantway of life for bacteria and a main mechanism for the formation of bacterialresistance. Compared with other countries, the abuse of antibiotics is very serious inChina, and the high MRSA detection rate as well. Therefore, the development of anew therapeutic strategy for inhibiting MRSA is imminent. Blue light could be apromising method for treating MRSA infection. The purpose of our study is toevaluate the antibacterial effects of blue light on both planktonic and biofilm stateMRSA in vitro and in vivo. Further to find an effective tool for clinically copingwith MRSA infection, and provide a new idea for eradicating other drug resistantbacterial infections.MethodsThis study investigated the role of blue light on inhibiting MRSA mainly throughthe following three parts:1. The study of the effect of blue light on planktonic state MRSA: MRSA were isolated from the wards at the department of Burn and PlasticSurgery, Shanghai No.3Hospital and identified by using ATBExpression. The MRSA were irradiated by blue light with fluencies of12、60、120and240J/cm2using a LED device respectively. Red light anduntreated groups were as control. After irradiation, the anti-bacteriaeffects of blue light were evaluated using colony counts andLIVE/DEAD staining.2. The study of the effect of blue light on killing biofilm state MRSA: MRSAwere incubated on glass coverslips for seven days and its appearancewere observed under inverted microscope every each day. According tothe results of part one, MRSA were irradiated with fluencies of120J/cm2,240J/cm2and360J/cm2respectively under blue light. Confocal laserscanning microscope (CLSM) and scanning electron microscopy wereapplied to evaluate the anti-MRSA effect of blue light.3. The study of the effect of blue light on wound MRSA infection: abioluminescent MRSA derived from ATCC33591was used in this part inorder to facilitate bacteria observation. Forty-eight SD mice were dividedinto control group and experimental group, all were made a2cm×2cmfull-thickness defect wound on the back, and injected1×1010CFU ofbacteria under the fascia. The control group did not receive any treatment,the experimental group was irradiated with fluencies of120J/cm2at day0,1,2,3,4,5,6,and day7post-injury. The antibacterial effect was observedthrough Fusion FX7scanning image analysis system.; HE staining wasused to assess inflammatory cells infiltration; The rate of wound healingwere calculated using image analysis software at different time points.Results:1. Our results shown that blue light has significant antibacterial effect with60J/cm2and above compared with control groups (P <0.01). Red light had no antibacterialeffect.2.240J/cm2is effective in killing biofilm stat MRSAand can destroy the structure of biofilm.3. Compared with control group, with continuously irradiation of blue light for6±0.9days, the majority of MRSA were killed and wound healed. There was nosignificant deference in inflammatory cell infiltration between two groups, but therewas a trend that treated group had less inflammation than control group. especiallyatday7post injury. Similarly, the healing time of wound in experimental group wasmuch shorter than that in control group..ConclusionsBlue light can effectively kill both planktonic and biofilm state MRSA in adose-effect manner, and can inhibit wound MRSA infection and facilitate woundhealing.