To study the antimicrobial activity of human umbilical cord mesenchymal stem cell(hUCMSC)supernatant and amoxicillin in staphylococcus aureus which isolated from burn wounds.

(1) hUCMSC were isolated from umbilical cord tissue of full-term healthy fetus after cesarean section and cultured. The third generation hUCMSC was inoculated into four 6-well plates, lipopolysaccharide was 100 ng/mL in one 6-well plate medium while no lipopolysaccharide in the other 6-well plates. The supernatant was extracted after corresponding culture for the following experiments. Staphylococcus aureus strains that come from Inner Mongolia Burn Medical Research Institute were selected for in vitro proliferation culture. As the random number table, divided into four groups: amoxicillin+ control(referred to as control group), amoxicillin+ hUCMSC supernatant (referred to as supernatant group), amoxicillin + hUCMSC supernatant + LL-37 antibody group (referred to as antibody group), amoxicillin + 100 ng/mL lipopolysaccharide pretreatment hUCMSC supernatant group (referred to as pretreatment group). At post culture hour 7, 12, 24 and 48, ten blood agar plates in each group. The minimum inhibitory concentration of amoxicillin against staphylococcus aureus of each group was recored. The fractional inhibitory concentration index of amoxicillin in this four group was calculated at post culture hour, and the effect of synergy was evaluated. (2) The experiment was the same as (1), ten blood agar plates in each group. When staphylococcus aureus strains were inoculated in vitro for 24 h, and each group staphylococcus aureus was stained near the antibacterial ring, than fixed, scanned by electron microscopy. (3) Data were processed with analysis of variance of factorial design, one-way analysis of variance, LSD-t test, Kruskal-Wallis test, Mann-Whitney test.

(1)At each post culture hour, the minimum inhibitory concentration of amoxicillin against staphylococcus aureus was higer in control group than those of supernatant group, antibody group and pretreatment group (with Z values from 6.609 to 6.655, P values below 0.05); The minimum inhibitory concentration of amoxicillin against staphylococcus aureus was higer in antibody group than those of supernatant group and pretreatment group (with Z values from 5.797 to 6.656, P values below 0.015); The minimum inhibitory concentration of amoxicillin against staphylococcus aureus was higer in supernatant group than those of pretreatment group (with Z values from 5.923 to 6.656, P values below 0.05). (2) Scanning electron microscopy results: the control group of staphylococcus aureus arranged to become loose, irregular, can not be gathered into grapes, the boundaries between cells slightly blurred, some of the boundaries between the cell body is obvious. Supernatant group of bacteria shape no circular structure, part of the cell wall, the membrane has been destroyed, showing a small amount of perforation membrane, cell wall degradation of polysaccharides in the vicinity of bacteria cells gathered, so that cells adhere to the lumps. The Antibody group of bacterial deformation, cell wall and cell membrane limit sensitive, cell membrane depression. Pretreatment of the cell membrane has been completely destroyed, showing a large number of perforation through the membrane, showing some of the cells disintegrated.

hUCMSC supernatant combined with amoxicillin antibacterial, can effectively reduce the amount of amoxicillin, hUCMSC supernatant synergistic antibacterial effect was significantly reduced after knockout LL-37. While, synergistic antibacterial action of lipopolysaccharide pretreatment hUCMSC supernatant is surpass hUCMSC supernatant.