Part1: Validation of Broad spectrum antibacterial function of PLA

    We used a certain concentration of PLA to effect on a variety of bacteria, and measured the residual amounts of bacteria over time to verify the broad spectrum antibacterial properties of PLA.
    Because of the limited strain of our laboratory, we completed this part in cooperation with other teams. We measured the inhibition effect of PLA on yeast Cen.PK2-1C, Staphylococcus aureus, Pseudomonas aeruginosa, yeast Cen.PK2-1D and other bacteria respectively (For details, please read the collaboration page). The collective data figure is as follows.

Fig.1 Growth of different initial value of OD Cen.PK2-1D under 16 mMol/L PLA

Fig.2 Growth of different initial value of OD Cen.PK2-1C under 16 mMol/L PLA

Fig.3 Growth of different initial value of OD Staphylococcus aureus under 0 mMol/L PLA, 10 mMol/L PLA, 15 mMol/L PLA, 200 mMol/L PLA.

Fig.4 Growth of different initial value of OD Pseudomonas aeruginosa under 0 mMol/L PLA, 10 mMol/L PLA, 15 mMol/L PLA, 200 mMol/L PLA.

    From the above data, we can clearly see that PLA can inhibit the growth of most bacteria, which directly proves its broad-spectrum antibacterial properties.

Part2: Practicability and Mechanism of PLA

（1）Quantitative Validation of bacteriostatic effect of PLA

    We used different concentrations of PLA to react with Staphylococcus epidermidis with different initial value of OD, and we measured the bacterial residue every hour and obtained the following formulas and diagrams.

Fig.5 Simulation of the number of bacteria colonies under different concentrations of PLA.

    Staphylococcus epidermidis is the main cause of armpit odor. From the above chart we can see that PLA has an effective inhibiting effect on Staphylococcus epidermidis, and the higher the concentration of PLA, the better the inhibition effect, which quantitatively proves the effectiveness of PLA and the practical feasibility of the products we used to treat armpit odor.

（2）Timeliness of PLA inhibition effect

    We used different concentrations of PLA to react with Staphylococcus epidermidis with different initial value of OD, and we measured the bacterial residue every hour and obtained the following formulas and diagrams.

Fig.6 Growth of saphylococcus epidermidis with an initial OD value of 1 under 11.25mmol/L of PLA

    In addition, we calculated the lowest optimum PLA concentration to inhibit Staphylococcus epidermidis, at which the growth rate of bacteria was always lower than the mortality rate. When PLA is higher than this concentration, the reaction rate will be faster.

（3）Validation of the breadth applicability of specific PLA concentration（Mechanism of PLA）

Fig.7 Growth of staphylococcus epidermidis with an initial OD value of 0.5 Abs under different concentrations of PLA

Fig.8 Growth of staphylococcus epidermidis with an initial OD value of 2 Abs under different concentrations of PLA

    Through these two figures, we learned that the effect of PLA in inhibiting the bacteria is independent to the initial OD value，which means the certain amount of PLA have the same inhibiting effect on the different amount of bacteria.
    The above analysis told us that under the same concentration of PLA, the number of strains inhibited by PLA is in proportion to the total number of current strains. Therefore, PLA is killing bacteria according to the proportion of bacteria, which also means that the data obtained by the above model are suitable for any number of Staphylococcus epidermidis.

Part3: Prove the practical feasibility of our products.

Fig.9 The result of demonstration experiment

    To summary, we have demonstrated our design in the laboratory, which proves that our antibacterial and aroma substances can solve the harmful bacteria and odors in the experiment more effectively.

Part4: Demonstrate the advantages of our products.

    The No. 1 plate showed the growth of the bacteria under normal conditions. The No. 2 plate was treated with soap, and the third was treated with hand sanitizer, and the No. 4 board was coated with our rose-scented bacteriostat. As shown in the figure, we can clearly see that the number of colonies on the No.2, No.3, and No.4 plates is reduced compared to the No. 1 plate. Among them, the soap of such brand has a relatively weaker antibacterial effect than the other two products. And the hand sanitizer is equivalent to our antibacterial and aroma-producing substances. Our rose-scented bacteriostatic and the hand sanitizer have comparable bacteriostatic effects.
    In addition, we use synthetic biology to produce such rose-scented bacteriostatic, reducing the burden on the environment and being safer and more friendly to people. To conclude, we have demonstrated the advantages of our products to better address people's needs and environmental issues in daily life.

Reference

[1] Ohhira I, Kuwaki S, Morita H, et al. Identification of 3-Phenyllactic Acid As a Possible Antibacterial Substance Produced by Enterococcus faecalis TH10[J]. Biocontrol Science. 2004, 9(3):77-81.
[2] Dieuleveux V, Lemarinier S, Guéguen M. Antimicrobial spectrum and target site of d -3-phenyllactic acid[J]. International Journal of Food Microbiology. 1998, 40(3):177.
[3] Russo P, Arena MP, Fiocco D, et al. Lactobacillus plantarum with broad antifungal activity: A promising approach to increase safety and shelf-life of cereal-based products[J]. International Journal of Food Microbiology. 2016, 247:48.